AT527841B1 - COAXIAL GEARBOX WITH INTEGRATED MEASURING SENSORS - Google Patents

Abstract

Coaxial transmission (1), comprising: - a piston set (5) with at least three pistons (10a-10p), wherein the pistons each have a toothing (12) with at least one tooth (13) on a first end face (11); - a hollow shaft (30) with an internal toothing (31), wherein the pistons are arranged within the hollow shaft (30); - a guide unit (8), wherein the pistons are each arranged in the guide unit (8) at a distance from one another in the circumferential direction (7) by guide webs (9) and are linearly guided to and fro in the radial direction (15); - a piston drive (3) for the linearly guided movement of the pistons, - wherein the toothings (12, 13) of the first end faces (11) of the pistons can be brought into engagement with the internal toothing (31) and into a state detached from the internal toothing (31) in order to continue rotating the hollow shaft (30) or the guide unit (9) about the axis of rotation (2) during the respective engagement, - at least one strain gauge (40, 41, 42) is fastened to at least one of the pistons.

Description

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Description

COAXIAL GEARBOX WITH INTEGRATED MEASURING SENSORS

FIELD OF THE INVENTION [0001] The present invention relates to a coaxial transmission comprising:

- at least one piston set with at least three pistons, wherein the pistons each have a toothing with at least one tooth on a first end face facing away from the axis of rotation;

- a hollow shaft with internal teeth, the pistons being arranged inside the hollow shaft when viewed in a plane normal to the axis of rotation;

- a guide unit, wherein the pistons of the respective piston set are each arranged in the guide unit at a distance from one another by guide webs in a circumferential direction pointing around the axis of rotation and are linearly guided and can be moved back and forth parallel to a radial direction normal to the axis of rotation;

- a piston drive for the linear guided movement of the pistons,

- wherein the toothings of the first end faces of the pistons can be brought, in particular one after the other, into engagement with the internal toothing and into a state detached from the internal toothing in order to continue to rotate the hollow shaft or the guide unit about the axis of rotation during the respective engagement, preferably with surface contact between the respective toothing and the internal toothing.

[0002] Furthermore, within the scope of the invention, a coaxial transmission according to the invention with an evaluation device for the acquisition and evaluation of measurement data is specified.

STATE OF THE ART

[0003] Numerous different designs of coaxial gears of the aforementioned type are already known. For example, single-stage planetary gears that operate coaxially, as well as multi-stage planetary gears, are each coaxial gears. Shaft gears, spur gears, eccentric gears, or cycloidal gears can also be designed as coaxial gears. By definition, coaxial gears have an input shaft and an output shaft on a common axis of rotation.

[0004] For example, US 4,713,985 A discloses a harmonic drive with a ring element. The ring element is arranged around the outer circumference of a cam element. A rotary movement of the cam element does not generate a rotary drive force, but rather forces the drive rollers of the ring element to move cyclically and radially. In one embodiment, a piezoelectric component is installed as an actuator in a central section of a multi-part connecting element of a drive roller of the ring element, whereby the actuator can be adjusted in length. A strain gauge records the change in length of the multi-part connecting element, which can also be used as a drive for the harmonic drive. A disadvantage, however, is that the use of such a length-adjustable connecting element reduces the rigidity and strength of the entire harmonic drive. A piston drive for a piston set with several pistons, each of which is moved linearly in the radial direction, is missing in the wave gear mentioned in US 4,713,985 A.

[0005] Coaxial transmissions, which comprise a piston drive for the linearly guided movement of the pistons of at least one piston set, include both transmissions without connecting rods, in which the piston drive is effected, for example, by means of a rotatable circular disk, elliptical disk or polygon disk, or by means of a piezo drive, as well as transmission designs in which the piston drive is effected by a crankshaft with at least one connecting rod bearing. In these embodiments

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guides of coaxial transmissions with crankshafts, at least one connecting rod is provided, wherein the at least one connecting rod is coupled to one or more pistons of the at least one piston set and to the at least one connecting rod bearing.

[0006] For example, various designs of coaxial transmissions with crankshafts are already known from EP 4 207 717 B1 and EP 4 004 406 B1 of the applicant. In these designs, the crankshaft represents a drive element or can be referred to as a drive element. The hollow shaft is preferably mounted for rotation about the axis of rotation and can function as an output element. Alternatively, with a fixed hollow shaft, the guide unit can function as the output element, for which the guide unit must be mounted for rotation.

[0007] Such coaxial gears, which are also referred to as crankshaft gears, can advantageously transmit high torques in a compact, small design, whereby a high transmission ratio as well as a high degree of accuracy and freedom from backlash are made possible with the coaxial gears in question.

[0008] While EP 4 004 406 B1 is based on a coaxial transmission in which at least three or more pistons are each connected to the at least one connecting rod bearing by means of a separate connecting rod, EP 4 207 717 B1 takes a different approach. WO 2023/088656 A1 corresponds to EP 4 207 717 B1. In the embodiment disclosed in EP 4 207 717 B1, a coaxial transmission is provided in which a common, star-shaped connecting rod is provided to connect the pistons of the respective piston set to the at least one connecting rod bearing or crank pin. By using a common "star connecting rod" for the pistons of a piston set, both the number of components and, consequently, the complexity and size of this coaxial transmission can be further reduced.

[0009] In such coaxial gears, the number of pistons that can be brought into engagement or partial engagement with the internal toothing of the hollow shaft can be varied as desired in order to adjust the transmission ratio and the level of transmittable torque as required. With at least three pistons, it can be ensured that the next piston, which presses the toothing of its first end face against the internal toothing, in particular flatly, does not rotate the hollow shaft or, if applicable, the guide unit back in the opposite direction, and that only a back-and-forth oscillation of the hollow shaft or the guide unit occurs around the axis of rotation.

[0010] Depending on the design of the piston drive, the engagement of the toothings of the first end faces of the pistons with the internal toothing of the hollow shaft can occur sequentially if, for example, a crankshaft is used as the piston drive. In the case of a piston drive, for example, by means of a cam disk, an elliptical disk, or a polygon disk, the toothings of two or more pistons can also engage simultaneously with the internal toothing of the hollow shaft. Such designs of piston drives are also encompassed by the invention.

[0011] The toothing of the first end faces of the pistons means that the respective piston can also be referred to as a “tooth element”.

[0012] The guide unit, which linearly guides the pistons of each piston set at a distance from one another by means of guide webs, can be constructed as a single piece or composed of multiple elements. The pistons are thus arranged distributed in the circumferential direction.

[0013] In the case that a coaxial transmission is equipped with two or more piston sets, it is also conceivable that the pistons of different piston sets are only axially spaced from each other, i.e. in the direction parallel to the axis of rotation.

[0014] Due to the advantages mentioned above, these coaxial gears are used in a wide variety of applications. However, in particular in applications where such coaxial gears are exposed to particularly high mechanical and/or thermal loads, the currently known generic coaxial gears offer only insufficient possibilities for a simple and reliable measurement data on loads during

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This is particularly important, for example, when using coaxial gearboxes for wind turbines, as the high forces caused by gusts of wind, turbulence, or tower vibrations, as well as the high thermal loads to which coaxial gearboxes are exposed, can lead to premature material fatigue and excessive wear, including material detachment and breakage of the gearboxes in question.

[0015] Other applications in which coaxial gears are subjected to particularly high gear loads include, for example, electric vehicle gears, where high load cycle forces occur, particularly during recuperation, and thus lead to high mechanical and thermal stress on the coaxial gears used. Coaxial gears used to drive actuating and positioning devices can also be subjected to high mechanical loads.

[0016] Monitoring a coaxial gearbox during operation has so far only been possible in a complex manner using external sensors. In particular, the reliable monitoring of robot drives requires the continuous recording and logging of operating parameters such as the detection of the angle of rotation of the drive and the angle of rotation of the output of the coaxial gearbox in question. However, for monitoring conventional coaxial gearboxes, an additional shaft must be passed through the hollow drive shaft, with the additional shaft being mounted on the gearbox output. While this makes it possible to record both the angle of rotation of the drive and the angle of rotation of the output on the drive side using one or more encoders, this disadvantageously reduces the inner diameter of the hollow shaft, requires additional components, and places high demands on complex assembly. Furthermore, with such an additional shaft, monitoring of the gearbox is only possible with a time delay due to the inertia of the encoders.

[0017] Encoders are measuring transducers or input devices that detect the current position of a shaft or drive unit and output it as an electrical signal. Encoders convert movement into an electrical signal that can be read by a control device in a motion control system, such as a programmable logic controller (PLC). The encoder sends a feedback signal that can be used to determine position, count, speed, or direction.

[0018] For example, in the case where the two detected angle of rotation values deviate too greatly from one another due to a broken tooth in the coaxial gear, a safety stop can be triggered, for example, by a control system. However, installing an additional shaft in the coaxial gear to detect the angles of rotation of the input shaft and the output shaft is structurally complex, cannot be retrofitted to existing coaxial gears, and typically increases the overall length of the coaxial gear in question. Another disadvantage is that with such conventional monitoring, possible setpoint deviations such as rising temperature or an above-average increase in friction cannot be detected early on during ongoing operation of the coaxial gear.

[0019] There is therefore an urgent need to be able to monitor particularly highly loaded coaxial gearboxes in a simple manner during operation in order to detect the mechanical and/or thermal loads to which the gearbox in question is exposed at an early stage and, in turn, to assess the wear and tear or condition of the gearbox and to plan the necessary maintenance work in good time.

OBJECT OF THE INVENTION

[0020] The object of the present invention is to provide an improved coaxial transmission that overcomes the aforementioned disadvantages. A further object of the invention is to provide an improved coaxial transmission including an evaluation device for acquiring measurement data obtained and evaluated during operation.

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PRESENTATION OF THE INVENTION [0021] To achieve the stated object, a coaxial transmission comprising:

- at least one piston set with at least three pistons, wherein the pistons each have a toothing with at least one tooth on a first end face facing away from a rotation axis;

- a hollow shaft with internal teeth, the pistons being arranged inside the hollow shaft when viewed in a plane normal to the axis of rotation;

- a guide unit, wherein the pistons of the respective piston set are each arranged in the guide unit at a distance from one another by guide webs in a circumferential direction pointing around the axis of rotation and are linearly guided and can be moved back and forth parallel to a radial direction normal to the axis of rotation;

- a piston drive for the linear guided movement of the pistons,

- wherein the toothings of the first end faces of the pistons can be brought, in particular successively, into engagement with the internal toothing and into a state detached from the internal toothing in order to further rotate the hollow shaft or the guide unit about the axis of rotation during the respective engagement, preferably with surface contact between the respective toothing and the internal toothing,

According to the invention, at least one strain gauge is attached to at least one of the pistons.

[0022] Strain gauges, or DMS for short, are measuring devices for detecting stretching and compressive deformations on the surface of components. Strain gauges can also be referred to as passive ohmic sensors or resistance elements. When a component, in this case a piston, to which at least one strain gauge is attached, is stretched or compressed, an initial length | of the DMS changes by a differential length Al, and an initial resistance R of the DMS (in ohms) changes by a differential resistance AR. The resistance change AR7/R is greater, the greater the strain € = Al.

[0023] With the present invention, it is possible to detect deviations from operating parameters during operation of the coaxial gear at an early stage by detecting and monitoring signals from at least one strain gauge.

[0024] If, for example, the stress curves of two consecutive periods of a strain gauge deviate too significantly from one another, this can have various causes, each of which triggers an operational stop of the coaxial gear. For example, the engagement of the gear teeth on the piston may have shifted compared to the internal gear teeth, material breakage may have occurred on the piston or gear teeth, foreign objects may have entered the interior of the coaxial gear, or the drive shaft may have broken. Detecting deviations during operation using one or more strain gauges attached directly to at least one piston is much faster and more precise than with conventional encoder systems. This is because, on the one hand, the inertia of strain gauges is very low, and, on the other hand, the expansion and compression of the piston are measured directly in situ at the point of force transmission and not via a kinematic chain.

[0025] The measurement data acquisition and evaluation of the resistance changes of the at least one strain gauge will be discussed in more detail below.

[0026] To monitor the torque, the input power in the drive motor is currently measured. If this exceeds a certain value, a safety stop is executed. The sensor system shown here significantly reduces the response time for overload detection by detecting voltage peaks in the strain gauge early and with short transmission times.

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[0027] A further advantage of the coaxial gear according to the invention is that the attachment of one or more strain gauges to at least one of the pistons does not influence or change the overall length of the coaxial gear. This makes it possible to retrofit existing coaxial gears with one or more strain gauges attached to at least one of the pistons. Advantageously, such retrofitting does not require any additional space in the coaxial gear for the measuring sensors of the at least one strain gauge.

[0028] Depending on the design, for the operation of the coaxial gear with integrated measuring sensors, either the guide webs adjacent to the respective piston equipped with at least one strain gauge can be fixed. In this design, the one or more strain gauges can each be connected to a downstream evaluation device for measuring data via signal lines for recording the resistance changes. The connecting cables or signal lines can be routed to the evaluation device in a twist-free manner through bores in the guide webs or the guide unit. The signal lines are expediently designed as flexible connecting cables that can withstand the linearly guided stroke movement of the respective piston. The connecting cables are preferably oversized so that the relevant cable connections are not subjected to mechanical stress or stretching even at maximum piston stroke.

[0029] Alternatively, for the operation of the coaxial gear with integrated measuring sensors, the ring gear can be fixed, whereby the signal transmission of the resistance changes of each strain gauge is carried out with a downstream evaluation device by means of sliding contacts or by means of radio contacts.

[0030] As will be explained in more detail below, the coaxial gear according to the invention can be used to determine both the current speed and the current angle of rotation, as well as the current direction of rotation, based on the signals detected by the at least one strain gauge. The coaxial gear according to the invention can be connected in a particularly flexible manner to a wide variety of drive units or drive motors and used for a wide variety of applications. For example, the piston drive of a coaxial gear according to the invention with integrated measuring sensors can also be implemented using a belt drive or an explosion-proof drive for safety reasons.

[0031] Further advantageous embodiments of the invention are set out in the dependent claims and in the following description. Furthermore, the positional information used for parts or components, such as the terms "top", "bottom", "above", "below", "front", "rear", "side", "inside", "outside", "in the axial direction", "in the radial direction" and the like, essentially serve to better understand the invention, in particular in conjunction with the following drawings. The positional information used may possibly refer to specific positions of individual parts or components of the coaxial transmission according to the invention or to individual views in the figures. In any case, such positional information is familiar to the person skilled in the art.

[0032] In a preferred embodiment of the invention, in a coaxial transmission, at least one strain gauge can be attached to at least three pistons, preferably arranged in a circumferential direction, particularly preferably uniformly, distributed.

[0033] As already mentioned at the beginning, with at least three pistons it can be ensured that the next piston, which presses with the toothing of its first end face against the internal toothing, in particular flatly, does not rotate the hollow shaft or, if applicable, the guide unit back in the opposite direction and that there is only a back-and-forth swing of the hollow shaft or the guide unit about the axis of rotation. By arranging at least one strain gauge on at least three pistons, which are preferably distributed in the circumferential direction, it is ensured that at least two pistons or toothed elements with their respective toothings are each at least partially in engagement with the internal toothing of the hollow shaft. With this arrangement, the respective applied torque can be determined.

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[0034] In the case of a piston drive, for example by means of a cam disc, it would even be conceivable to design such a coaxial transmission with only two pistons.

[0035] In order to ensure the most even distribution possible in the circumferential direction of the pistons, each equipped with one or more strain gauges, in a coaxial transmission according to the invention, the at least one piston set can comprise an even number of at least six pistons, with at least one strain gauge being attached to at least every other piston. For example, a piston set can comprise sixteen pistons, with at least one strain gauge being arranged on every other piston, thus providing a total of at least eight strain gauges.

[0036] A particularly precise, high-resolution monitoring of the ongoing operation of a coaxial transmission according to the invention can be achieved if at least one strain gauge is attached to each piston.

[0037] In order to fasten the at least one strain gauge to the respective piston in a coaxial transmission according to the invention in such a way that it is outside the force flow which occurs as a result of the torque transmitted from the ring gear into the guide web, the at least one strain gauge can be arranged in a first piston segment on the respective piston, wherein the first piston segment forms an outer surface section on the respective piston and is positioned in the radial direction parallel to a piston longitudinal axis and at least in sections normal to an orientation direction of the at least one tooth of the respective piston.

[0038] In the case where only one strain gauge is arranged per piston or per tooth element, a so-called Wheatstone quarter bridge with three additional resistors is used to evaluate the resistance change of the strain gauge. Temperature compensation is required to determine the resistance change with as little influence as possible from temperature. Temperature compensation can either be implemented directly in the circuit or be considered during signal evaluation.

[0039] In an advantageous development of the invention, in a coaxial transmission, at least two strain gauges can be attached to at least one, preferably to at least three pistons arranged distributed in the circumferential direction.

[0040] The use of at least two strain gauges on one and the same piston offers the advantage that the second strain gauge can either serve as a half-bridge circuit for temperature compensation or can be used as a redundant measuring device, with which the reliability and failure safety of the measuring sensor is further improved if the first strain gauge is defective.

[0041] If, for example, there is sufficient space on a large coaxial gearbox with large pistons to mount four strain gauges on one and the same piston, the four strain gauges can be connected as a full bridge. In this configuration, common-mode suppression, for example of interference on the sensor line, can be achieved in order to obtain particularly precise measurement signals. In the case where four strain gauges are mounted on the same side of a piston, this arrangement can also be used to record and evaluate the bending forces acting on the piston during gearbox operation.

[0042] In a further preferred embodiment of the invention, in a coaxial transmission, a first strain gauge in a first piston segment and a second strain gauge in a second piston segment opposite the first piston segment can be arranged on the same piston, wherein the first piston segment and the second piston segment each form an outer surface section on the respective piston and are each positioned in the radial direction parallel to a piston longitudinal axis and at least in sections normal to an orientation direction of the at least one tooth of the respective piston.

[0043] In this arrangement, two strain gauges are advantageously connected to one

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Each piston is attached to opposite piston segments on the respective piston in such a way that they are each outside the force flow that occurs due to the torque transmitted from the ring gear into the guide web.

[0044] In order to be able to attach the strain gauges to the respective piston with as little mechanical damage as possible, in a further advantageous embodiment of the invention, in a coaxial transmission, a first piston segment and/or a second piston segment is/are each formed as a chamfered outer surface section on the respective piston, wherein preferably a chamfer width of the first piston segment and/or a chamfer width of the second piston segment is/are each greater than or equal to a width of a strain gauge. By chamfering one or two outer surface sections on the piston, sufficient space or clearance is created to attach one or more strain gauges to the respective piston segment without the strain gauges touching the adjacent guide webs of the guide unit.

[0045] Alternatively or in addition to one or more chamfered outer surface sections on the respective piston, it is further provided within the scope of the invention that a web recess can be arranged on the respectively adjacent guide web of the guide unit corresponding to the position of a first piston segment and/or corresponding to the position of a second piston segment of the respective piston, wherein the respective web recess runs in the radial direction parallel to the piston longitudinal axis of the respective piston and the at least one strain gauge is arranged at least in sections in the web recess, wherein the respective web recess preferably has a recess width which is greater than or equal to a width of a strain gauge. In this embodiment, the web recess in the guide web forms the necessary clearance for the strain gauge on the adjacent piston in order to prevent the strain gauge from rubbing against the guide web.

[0046] In order to provide a coaxial transmission according to the invention which is as versatile and flexible as possible for a wide variety of applications, the at least one strain gauge can be selected from the group comprising or consisting of: foil strain gauges, semiconductor strain gauges, rosette strain gauges, wire strain gauges.

[0047] Foil strain gauges are usually laminated onto a thin plastic carrier and firmly bonded to the carrier, in this case the respective piston. The combination of several strain gauges on a carrier in a partially overlapping arrangement is referred to as a rosette strain gauge or strain gauge rosette. Due to a piezoresistive effect, semiconductor strain gauges offer the advantage of relatively high k-factors, i.e., high sensitivities, and particularly compact dimensions. Wire strain gauges offer the advantage of being able to be used even at high operating temperatures.

[0048] In a preferred embodiment of the invention, in a coaxial transmission, the piston drive can comprise a crankshaft rotatable about the axis of rotation with at least one connecting rod bearing, wherein at least one connecting rod is provided, which connecting rod is coupled to one or more pistons of the at least one piston set and to the at least one connecting rod bearing.

[0049] Such coaxial gears, which are also referred to as crankshaft gears, can advantageously transmit high torques in a compact, small design, whereby a high transmission ratio as well as a high degree of accuracy and freedom from backlash are made possible with the coaxial gears in question.

[0050] Alternatively, in a further preferred embodiment of the coaxial transmission according to the invention, it can be provided that the piston drive comprises at least one cam disc or piezo elements or linear motors rotatable about the axis of rotation.

[0051] In order to provide a particularly compact design of a coaxial gearbox,

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In a further embodiment according to the invention, a common, star-shaped connecting rod, to which the pistons of the respective piston set are coupled, can be provided for connecting the pistons of the respective piston set to the at least one connecting rod bearing.

[0052] To couple the pistons of the respective piston set to the associated star-shaped connecting rod, elongated holes may be provided in the pistons, with the elongated holes extending transversely to the radial direction. In this design, coupling bolts are attached to the star-shaped connecting rod, which engage with the elongated holes.

[0053] Alternatively, a separate connecting rod can be provided to connect each piston of the respective piston set to the at least one connecting rod bearing.

[0054] The object mentioned at the outset is also achieved with a system according to the invention comprising a coaxial gear and an evaluation device for the acquisition and evaluation of measurement data, wherein

- the evaluation device comprises a measurement data acquisition unit and a measurement data analysis unit, wherein

- the measurement data acquisition unit is signal-connected to the at least one, preferably to at least three, particularly preferably to all, strain gauges of the coaxial transmission, and the measurement data acquisition unit is configured to detect resistance changes of each of the strain gauges by means of at least one bridge circuit and outputs corresponding voltage signals, and wherein

- the measurement data analysis unit is configured to determine at least one actual value signal of a current rotational speed and/or a current rotational angle position and/or direction of rotation and/or a current torque and/or a current temperature and/or a currently acting force on the basis of the voltage signals output by the measurement data acquisition unit of each of the strain gauges, and preferably to output said actual value signal to a control device and/or to an external data monitoring device.

[0055] Depending on the number, positioning, and configuration of the strain gauges used, the measurement data acquisition unit can also determine several or all of the aforementioned operating parameters, including: a current rotational speed, a current rotational angle, the current rotational direction, a current torque; a current temperature, and/or a currently acting force. With regard to the currently acting force, it is hereby clarified that the respective strain gauge detects the mechanical stress acting on the respective piston to which the strain gauge is attached, i.e., an elongation or compression of the piston. Thus, strictly speaking, the respective strain gauge determines the force acting on the respective piston or the torque acting on the coaxial gear.

[0056] A coaxial gear unit according to the invention, together with an associated evaluation device for acquiring and evaluating measurement data, can be used in a particularly flexible manner for a wide variety of applications. As already mentioned above, in principle, any drive motor can be connected to the coaxial gear unit and coupled to it. Advantageously, the evaluation unit is also configured to be "manufacturer-independent" and can process the measurement signals or voltage signals from different strain gauges regardless of the respective strain gauge manufacturer.

[0057] The measurement data acquisition unit may, in addition to the at least one bridge circuit for detecting resistance changes of each of the strain gauges and at least one measuring amplifier in order to be able to output corresponding voltage signals, comprise at least one or more of the following further electronic components and components for signal calibration or signal standardization: a further signal value amplifier, an A/D converter (analog-digital converter), an electronic component for signal value standardization, an electronic component for zero value standardization, an electronic component for signal value standardization including signal value adjustment by means of signal offset, a voltage limiter, and/

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or a D/A converter (digital-to-analog converter). The at least one measuring amplifier can be configured to provide a DC voltage for applying voltage to the strain gauges.

[0058] The measurement data analysis unit may, for example, comprise a CPU computing processor, a working memory, a data storage device including a configuration data memory used to store configuration data, and a signal converter.

[0059] Advantageously, the system according to the invention can be used, for example, to determine the rotational speed of the hollow shaft or the guide unit, wherein the evaluation device is configured to determine at least one actual value signal of a current rotational speed. A method for determining a current rotational speed using the system according to the invention comprises the following steps:

- detecting and evaluating the voltage signals of at least one strain gauge, preferably all strain gauges, during operation of the coaxial gear;

- Determining a period P as the time interval between two corresponding voltage peaks of the voltage signal of the strain gauge in question;

- Convert the period P taking into account the number L of gaps in the internal gearing of the hollow shaft into a current rotational speed @=(27/L)/P.

[0060] In order to determine the current rotational speed of the hollow shaft or the guide unit of the coaxial gear, the period P is evaluated as the time interval t2-t1 between two corresponding voltage peaks of the voltage signal of the respective strain gauge.

[0061] The angle of rotation corresponding to a period P is ®=27/L. [0062] L denotes the number of gaps in the internal gearing of the hollow shaft. [0063] The rotational speed m=®/P=(27/L)/P is given in [rad/s].

[0064] To determine the rotational speed, the period duration is also evaluated as the time interval between two corresponding voltage peaks of the voltage signal of the respective strain gauge. The period duration is directly proportional to the rotational speed. For example, with a gear reduction ratio of 100:1, 100 piston strokes are required to achieve one revolution of the hollow shaft or the guide unit of the coaxial gear. The distance between two corresponding voltage peaks in this case corresponds to a rotation angle ® of 3.6°. The period duration defines the rotational speed.

[0065] To determine the direction of rotation, the sequence of the incoming voltage signals from at least two strain gauges attached to different pistons must be evaluated. For example, a signal sequence of the incoming voltage signals from the strain gauges first at the first piston and with a time delay at the second piston is opposite to a signal sequence of the incoming voltage signals from the strain gauges first at the second piston and then, or with a time delay, at the first piston.

[0066] In order to be able to determine the current angular position of the hollow shaft or the guide unit using the system according to the invention, the evaluation device is configured to determine at least one actual value signal of a current angular position. A method for determining a current angular position using the system according to the invention comprises the following steps:

- detecting and evaluating the voltage signals of at least one strain gauge, preferably all strain gauges, during operation of the coaxial gear;

- Determining the respective times of voltage peaks of the strain gauge in question;

- Assignment of the respective times of stress peaks taking into account the number of gaps L of the internal gearing of the hollow shaft as an increment of a current rotational angle position of the strain gauge in question.

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[0067] If the times t4, t2,..., tn are corresponding stress peaks, then n is the number of periods P or gaps L or recesses in the internal gearing into which the respective piston has engaged. In the time interval from time t0=0 to time t, the hollow shaft or the guide unit of the coaxial gear has therefore rotated further by a differential angle of rotation A®=n: 27/L.

[0068] The current rotation angle position is then ®=®,+A®, where %, is a known rotation angle at time t0=0.

[0069] In order to record the angular position, the respective times of stress peaks are assigned as an increment of a current angular position of the respective strain gauge, taking into account the number of gaps L of the internal gearing of the hollow shaft. The pulse of a stress peak can, for example, be evaluated as an increment for a rotation angle © of 3.6° (corresponding to the example above). The more pistons or "tooth elements" are subjected to strain gauges, the higher the resolution of the overall system. In a coaxial gearbox in which, for example, 16 pistons are equipped with strain gauges, 16 measuring pulses result per 3.6° angle of rotation. This allows the angular position to be resolved with an accuracy of 0.225° angle of rotation steps. If the characteristics of the measuring signals are also taken into account, three (or more) significant, corresponding stress peaks can be evaluated per tooth engagement. For example, the corresponding stress peaks can be recorded at the moment of tooth engagement, at the moment of stress peaks at the highest load during tooth engagement, and/or at the moment of extension upon disengagement. This allows the resolution of the angular position to be further increased, and the angular position can be specified, for example, with an accuracy of 0.225°/3, i.e., in 0.075° angle increments. The accuracy of the angle determination can be further increased using more extensive signal analysis.

[0070] The system according to the invention can also be used to determine the current torque of the coaxial transmission. The evaluation device is configured to determine at least one actual value signal of a current torque. A method for determining a current torque using the system according to the invention comprises the following steps:

- detecting and evaluating the voltage signals of at least one strain gauge, preferably all strain gauges, during operation of the coaxial gear;

- Calibrating the at least one strain gauge, preferably all strain gauges, at predefined torques and assigning the respective voltage amplitudes of voltage peaks of the respective strain gauge to a calibrated torque value;

- Comparing the respective current voltage amplitudes of voltage peaks of the respective strain gauge during operation of the coaxial gear with the calibrated torque values and determining a current torque.

[0071] The step of calibrating at least one strain gauge or all strain gauges is generally to be carried out only once at the beginning of the measurements.

[0072] The torque is determined by evaluating the voltage amplitude. The signal is recorded for different torques in the assembled state of the coaxial gear, and the system is calibrated using this. A specific voltage amplitude is assigned to a calibrated torque value. A mathematical calculation is difficult to solve analytically due to the numerous influences caused by friction or manufacturing deviations in the actual operation of the coaxial gear. Using numerical methods, a factor k can be determined, which depends on the speed, the temperature, and the material properties of the respective strain gauge. Since each strain gauge has individual material properties according to the respective data sheet, these must be

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be taken into account in the calibration.

[0073] The respective torque M can therefore be determined as a function of the factor and the resulting force Fries: M=Kk:Fres

[0074] The system according to the invention can also be used to determine a current temperature within the coaxial transmission or at the location of the respective strain gauge. For this purpose, the evaluation device is configured to determine at least one actual value signal of a current temperature. A method for determining a current temperature using the system according to the invention comprises the following steps:

- detecting and evaluating the voltage signals of at least one strain gauge, preferably all strain gauges, during operation of the coaxial gear;

- Calibrating the at least one strain gauge, preferably all strain gauges, at predefined temperatures and assigning an offset of the respective voltage signal of the respective strain gauge to a known temperature value prevailing during calibration;

- Determining corresponding voltage peaks of the voltage signal of the strain gauge in question over time and determining the slope S of a signal drift;

- Calculation of a relative temperature change AT by multiplying S by a corresponding known material constant of the strain gauge in question;

- Determining an initial temperature To based on the offset of the voltage signal in an initial time range;

- Determine the current temperature T by adding To and AT.

[0075] The slope S of the signal drift provides information about the relative temperature change. As the operating temperature increases, the voltage signal moves to higher voltage values. The signal range (e.g., 0-10 V) must therefore lie within the temperature range expected during operation of the coaxial gear. The characteristic of the temperature behavior of the strain gauge in question can be determined from its temperature coefficient (Temp. Coefficient of Gauge Factor), i.e., a material constant according to the strain gauge data sheet. This allows the measuring range of the voltage signals to be adjusted according to the expected temperature range during operation of the coaxial gear.

SHORT DESCRIPTION OF THE CHARACTERS

[0076] The invention will now be explained in more detail with reference to exemplary embodiments. The schematic drawings are each exemplary and are intended to illustrate the inventive concept.

[0077] Showing:

[0078] Fig. 1 shows a schematic sectional view of a first embodiment of a coaxial transmission according to the invention;

[0079] Fig. 2 shows an isometric view obliquely from the side of a piston of a coaxial transmission according to the invention with a strain gauge attached thereto;

[0080] Fig. 3 shows an isometric view, partially cut away, of a piston of a coaxial transmission according to the invention with two strain gauges attached thereto;

[0081] Fig. 4 is a partial sectional view from above of the piston shown in Fig. 3 with chamfered piston segments for receiving the strain gauges within a guide unit;

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[0082] Fig. 5 shows a partially sectional view from above of a piston of a coaxial transmission according to the invention with two strain gauges attached thereto within a guide unit with web recesses;

[0083] Fig. 6 shows the first embodiment of a coaxial transmission according to the invention shown in Fig. 1 with further details;

[0084] Fig. 7 shows the coaxial transmission shown in Fig. 6 in a sectional view from the side according to the section plane A-A shown in Fig. 6;

[0085] Fig. 8 shows a schematic sectional view of a second embodiment of a coaxial transmission according to the invention;

[0086] Fig. 9 shows the coaxial transmission shown in Fig. 8 in a sectional view from the side according to the section plane B-B shown in Fig. 8;

[0087] Fig. 10 is a schematic signal flow diagram of a system of a coaxial transmission according to the invention with an evaluation device for the acquisition and evaluation of measurement data;

[0088] Fig. 11 is a schematic circuit diagram of a Wheatstone bridge circuit of a quarter bridge;

[0089] Fig. 12 is a schematic signal flow diagram of an embodiment of a measurement signal recording device according to the invention;

[0090] Fig. 13 shows in a diagram the voltage curve of a measuring signal over time.

WAYS OF IMPLEMENTING THE INVENTION

[0091] Fig. 1 shows a coaxial transmission 1 according to the invention in a schematic view of a section normal to a rotational axis 2.

[0092] The coaxial transmission 1 comprises a piston drive 3, which here, for example, comprises a crankshaft 3a rotatable about the rotational axis and having at least one connecting rod bearing 4. In the present embodiment, exactly one connecting rod bearing 4 or exactly one crankpin or connecting rod journal is provided. Details of the piston drive 3 will be discussed below.

[0093] The coaxial transmission 1 of the first embodiment further comprises a piston set 5 with sixteen pistons 10, which are designated clockwise in Fig. 1 as pistons 10a-10p. The piston drive 3 serves for the linearly guided movement of the pistons 10a-10p. Each piston 10a-10p has a toothing 12 with at least one tooth 13 on a first end face 11 facing away from the rotational axis.

[0094] The pistons 10a-10p of the respective piston set 5 are each arranged in a guide unit 8, spaced apart from one another by guide webs 9 in a circumferential direction 7 pointing around the rotation axis 2. The guide unit 8 or the guide webs 9 between adjacent pistons 10 serve to guide the pistons 10a-10p linearly, so that the pistons 10-10p can be moved back and forth parallel to a radial direction perpendicular to the rotation axis 2. The circumferential direction 7 is symbolized by a double arrow 7.

[0095] Furthermore, the coaxial transmission 1 shown comprises a hollow shaft 30 with an internal toothing 31, wherein the pistons 10a10p are arranged within the hollow shaft 30, viewed in a plane normal to the rotational axis 2. The internal toothing 31 has a plurality of gaps 32 or recesses.

[0096] The toothings 12, 13 of the first end faces 11 of the pistons 10a-10p can be brought into engagement with the internal toothing 31, in particular one after the other, and can also be brought into a state detached from the internal toothing 31 in order to rotate the hollow shaft 30 or the guide unit 9 around the rotational axis during the respective engagement of one or more teeth 13 in corresponding gaps 32 or recesses of the internal toothing 31, preferably with surface contact between the respective toothing 12, 13 and the internal toothing 31.

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axis 2 to continue rotating.

[0097] According to the invention, at least one strain gauge 40 is attached to at least one of the pistons 10a-10p. In the first embodiment shown in Fig. 1, a strain gauge 40 is alternately attached to every other piston 10a, 10c, 10e, 10g, 10i, 10k, 10m, 100. The strain gauges 40 shown here are designed, for example, as foil strain gauges 41, in particular as semiconductor strain gauges 42, and offer the advantage of having high k-values with high sensitivities and being particularly compact. To clearly assign the individual strain gauges 40 to the respective piston 10a, 10c, 10e, 10g, 10i, 10k, 10m, 100 to which they are attached, the foil strain gauges are designated clockwise with the reference numerals 41a-41h. Within the scope of the invention, one or more of the strain gauges can also be designed as wire strain gauges or arranged in a rosette shape.

[0098] Fig. 2 shows, by way of example, an isometric view of such a piston 10, for example the piston 10a shown in Fig. 1. The tooth 13 has a first tooth flank 13a, a second tooth flank 13b, a tooth width 13c, an orientation direction 13d of the tooth 13, which is symbolized by a double arrow 13d, and a tooth height 13e. The piston 10, 10a has a piston longitudinal axis 14. The piston longitudinal axis 14 corresponds to the radial direction 15, symbolized by a double arrow 15, in which the piston 10, 10a is movable back and forth. The piston 10, 10a shown has a bore 16 for a piston pin (not shown) with a longitudinal axis direction 17. Furthermore, a recess 20 is provided for a connecting rod connection.

[0099] The strain gauge 40, 41, 42 is arranged in a first piston segment 18 on the piston 10, 10a, wherein the first piston segment 18 forms an outer surface portion on the piston 10a and is positioned in the radial direction 15 parallel to the piston longitudinal axis 14 and at least partially normal to the orientation direction 13d of the tooth 13. The first piston segment 18 is designed here as a chamfered outer surface portion with a chamfer width 18a. The chamfer width 18a is selected here, for example, such that it is greater than a width 40a of the respective strain gauge 40. A second piston segment 19 is formed opposite the first piston segment 18 in the orientation direction 13d of the tooth 13, wherein the second piston segment 19 also forms an outer surface section on the piston 10a and is positioned in the radial direction 15 parallel to the piston longitudinal axis 14 and at least partially normal to the orientation direction 13d of the tooth 13. For example, the second piston segment 19 can also be chamfered.

[00100] In the following, identical or comparable parts and components of different design variants are each designated by the same reference numerals.

[00101] Fig. 3 shows a partially cutaway view of a piston 10 of a coaxial transmission 1 according to the invention with two strain gauges 40 attached thereto.

[00102] Fig. 4 shows a partial sectional view from above of the piston 10 shown in Fig. 3 with chamfered piston segments 18, 19 for receiving the strain gauges 40 within a guide unit 9. The following description applies equally to both figures Fig. 3 and Fig. 4.

[00103] On the piston 10, a first piston segment 18 and a second piston segment 19 are each formed as a chamfered outer surface section, wherein a chamfer width 18a of the first piston segment 18 and a chamfer width 19a of the second piston segment 19 are each at least equal to a width 40a of a strain gauge 40, 41, 42. The first piston segment 18 and the second piston segment 19 each form an outer surface section on the piston 10 and are each positioned in the radial direction 15 parallel to the piston longitudinal axis 14 and at least partially normal to an orientation direction 13d of the tooth 13 of the respective piston 10. Figure 3 also shows a connecting rod 6, a piston pin 21, which is inserted in the longitudinal axis direction 17 within the bore 16 of the piston 10 and enables an articulated coupling of the piston 10 with the connecting rod 6, as well as sections

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the guide unit 8 and the guide webs 9 adjacent to the piston 10. The tooth 13 on the first end face 11 of the piston 10 engages in corresponding gaps 32 or recesses of the internal toothing 31, which is arranged on the inside of the hollow shaft 30.

[00104] Fig. 5 shows a partial sectional view from above of a piston 10 of a coaxial transmission 1 according to the invention with two strain gauges 40 attached thereto within a guide unit 8 with web recesses 29.

[00105] Corresponding to the position of a first piston segment 18 and corresponding to the position of a second piston segment 19 of the respective piston 10 on the respectively adjacent guide web 9 of the guide unit 8, a web recess 29 is arranged here, wherein the respective web recess 29 runs in the radial direction 15 parallel to the piston longitudinal axis 14 of the respective piston 10. The two strain gauges 40, 41, 42 are fastened to the piston 10 such that they are arranged here in the web recess 29, wherein the respective web recess 29 has a recess width 29a which is greater than or equal to the width 40a of the respective strain gauge 40, 41, 42.

[00106] Fig. 6 again shows the first embodiment of a coaxial transmission according to the invention, already shown in Fig. 1. Reference is made to the above for the basic functioning of the coaxial transmission 1. Since the specific design of the respective piston drive 3 is of only secondary importance in the present invention, further details on the piston drive 3 with a crankshaft 3a can be found in Fig. 6—in addition to Fig. 1.

[00107] In this embodiment, the pistons 10a-10p of the piston set 5 are coupled to the connecting rod 6, which is designed here as a star-shaped connecting rod 60, by means of intermediate links 22. The intermediate links 22 are essentially rigid, with each intermediate link 22 being pivotally connected, on the one hand, to the respective associated piston 10a-10p by means of guide pins 23 and, on the other hand, being pivotally connected to the star-shaped connecting rod 60 by means of connecting pins 25. The connecting pins 25 define pivot joints 27, the axes of rotation of which are parallel to the axis of rotation 2. In this view, the strain gauges 40 are attached to the respective piston 10 in such a way that they are each located outside the force flow caused by the torque transmitted from the ring gear 30 into the guide web 9 of the guide unit 8.

[00108] Fig. 7 is a sectional view of the coaxial transmission 1 from the side according to the sectional plane A-A shown in Fig. 6. In this side view, the strain gauges 40 attached to the pistons 10 are not visible.

[00109] Fig. 8 shows a schematic sectional view of a second embodiment of a coaxial transmission 1 according to the invention.

[00110] The coaxial transmission 1 comprises a piston drive 3 with a crankshaft 3a rotatable about the rotational axis 2 with at least one connecting rod bearing 4, wherein in the illustrated embodiment exactly one connecting rod bearing 4 or exactly one crankpin or connecting rod pin is provided.

[00111] Here, three pistons 10a, 10b, 10c are connected to the connecting rod bearing 4 in a manner known per se, or the pistons 10a, 10b, 10c are movably mounted on the connecting rod bearing 4. For example, a split connecting rod eye of each of the connecting rods 6a, 6b, 6c is fastened to the connecting rod bearing 4 by means of screws, and pistons 10a, 10b, 10c are connected to further connecting rod eyes of the connecting rods 6a, 6b, 6c via piston pins 21. In the embodiment of Fig. 8, a total of five pistons 10 are provided, with only the three pistons 10a, 10b, 10c being visible. The piston 10a is connected to the crankshaft 3a or the connecting rod bearing 4 via the connecting rod 6a, the piston 10b via the connecting rod 6b and the piston 10c via the connecting rod 6c.

[00112] All pistons 10a, 10b, 10c each have a first end face 11 pointing away from the axis of rotation 2 with an embossed toothing 12, wherein the respective toothing 12 in the illustrated embodiment each has exactly one tooth 13.

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[00113] In the illustrated embodiment, the crankshaft 3a is hollow along the axis of rotation 2, which, for example, allows cables (not shown) to be passed through without twisting. Furthermore, the coaxial transmission 1 features a hollow shaft 30 having internal gearing 31. In the image plane of Fig. 8, which is perpendicular to the axis of rotation 2, the pistons 10a, 10b, 10e—and at least in sections the crankshaft 3a—are arranged within the hollow shaft 30. This also applies to a guide unit 8, in which the pistons 10a, 10b, 10c are each guided linearly and can be moved back and forth parallel to a radial direction 15 perpendicular to the axis of rotation 2. For this purpose, the guide unit 9 in the illustrated embodiment has guide webs 9 in the form of hollow cylinders, which function as linear guides for the pistons 10a, 10b, 10c.

[00114] By moving the pistons 10a, 10b, 10c back and forth, the toothings 12 on the first end faces 11 of the pistons 10a, 10b, 10c are successively brought into engagement with the internal toothing 31 and into a state detached from the internal toothing 31, wherein, due to the linear movement of the pistons 10a, 10b, 10c during the respective engagement, a surface contact between the respective toothing 12, 13 and the internal toothing 31 can be ensured. The respective toothing 12, 13 is pressed flat against the internal toothing 31 of the hollow shaft 30.

[00115] This causes the hollow shaft 30 to rotate a little further about the rotational axis 2 if the guide unit 9 is arranged immovably relative to the rotational axis 2, or if the guide unit 8 is arranged to rotate about the rotational axis 2 but is braked. However, if the hollow shaft 30 is fixed or immovable relative to the rotational axis 2, or is braked, the guide unit 8, which is mounted to rotate about the rotational axis 2, is rotated a little further. Due to the surface engagement or pressing, very high torques can be transmitted from the crankshaft 3a to the hollow shaft 30 or, if applicable, to the guide unit 9.

[00116] A strain gauge 40 is attached to each of the five pistons 10 (of which the three pistons 10a, 10b, 10c are visible), thus a total of five strain gauges 40 are provided in this coaxial gear 1.

[00117] Fig. 9 shows the coaxial transmission 1 shown in Fig. 8 in a sectional view from the side according to the sectional plane B-B shown in Fig. 8. In Fig. 9, a fourth piston 10c' and an associated connecting rod 6c' as well as a connecting rod 6a' of a fifth piston (not shown, this piston is located behind the elements shown in Fig. 8 when viewed in the direction of the drawing plane of Fig. 8 or is the last piston when viewed along the axis of rotation 2, with piston 10a being the first) can also be seen.

[00118] In this side view, the strain gauges 40 attached to the pistons 10 are not visible.

[00119] Fig. 10 shows a schematic signal flow diagram of a system of a coaxial transmission 1 according to the invention with an evaluation device 100 for the acquisition and evaluation of measurement data.

[00120] The evaluation device 100 comprises a measurement data acquisition unit 110 and a measurement data analysis unit 130. The measurement data acquisition unit 110 is connected to at least one, preferably to at least three, and as illustrated here in Fig. 10, particularly preferably to all, strain gauges 40, 41a-41h of the coaxial transmission 1 by means of signal lines 90. The signal lines 90 serve as connecting cables for the signal transmission of the resistance changes. Alternatively, the signal transmission between the strain gauges 40, 41a-41h and the evaluation device 100 can take place, for example, via radio. However, this requires a voltage supply to the strain gauges 40, 41a-41h, for example, via slip ring contacts or conventional connecting cables.

[00121] In Fig. 10, the measurement data acquisition unit 110 comprises at least one bridge circuit 111, a first measuring amplifier 112 and optionally an A/D converter 113. The measurement data acquisition unit 110 is designed to detect resistance changes or diagonal voltages.

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voltages 81 and 81a, 81b of each of the strain gauges 40, 41a-41h are set up by means of at least one bridge circuit 111 and outputs corresponding voltage signals 121.

[00122] The measurement data analysis unit 130 is configured to determine, on the basis of the voltage signals 121 output by the measurement data acquisition unit 110 of each of the strain gauges 40, 41a-41h, at least one actual value signal 140 of a current rotational speed and/or a current rotational angle position and/or rotational direction and/or a current torque and/or a current temperature and/or a currently acting force, and preferably to output it to a control device 150 and/or to an external data monitoring device 160.

[00123] The measurement data analysis unit here comprises, for example, a CPU processor 131, a working memory 132, a device 135 for data storage including a configuration data memory 136, which serves to store configuration data, and a signal converter 140.

[00124] Fig. 11 shows a schematic circuit diagram of a Wheatstone bridge circuit 111 of a quarter bridge. The Wheatstone measuring bridge 70 shown here comprises a total of four resistors: a first resistor 71, a second resistor 72, a third resistor 73, and a fourth resistor 74. One of the resistors 71-74 is the strain gauge 40. A voltage 80 is applied. The change in the resistance of the strain gauge 40 is detected by the bridge circuit 111 as a diagonal voltage 81 and fed into a measuring amplifier 112 as a voltage signal 81 or 81a, 81b, as symbolized in Fig. 10.

[00125] Fig. 12 shows a schematic signal flow diagram of an embodiment of a measurement signal recording system according to the invention. Essentially, Fig. 12 shows the measurement signal recording system within the measurement data acquisition unit 110 in further detail.

[00126] The measurement data acquisition unit 110 shown here comprises, in addition to at least one bridge circuit 111 for detecting resistance changes of each of the strain gauges 40 and a measuring amplifier 112 in order to be able to output corresponding voltage signals, the following further electronic parts and components for signal calibration or signal normalization: an A/D converter 113 (analog-digital converter), an electronic component 114 for signal value normalization, an electronic component 115 for zero value normalization, a further signal value amplifier 116, an electronic component 117 for signal value normalization including signal value adjustment by means of signal offset, a first voltage limiter 118, a D/A converter 119 (digital-analog converter) and a second voltage limiter 120. The measuring amplifier 112 only amplifies the voltage signal 81. The provision of an applied voltage 80, preferably a DC voltage, for applying the strain gauge 40 is done separately.

[00127] The resistance change measured by the at least one strain gauge 40 is recorded in the bridge circuit 111 as a diagonal voltage 81 and initially amplified in the measuring amplifier 112. The amplified (or increased) voltage 82 is then converted in the A/D converter 113. A raw signal 82a obtained in this way is normalized in a device 114 for signal value normalization. The obtained normalized signal 82b is set to "zero" in a subsequent device 115 for zero value normalization, whereby any signal deviations and inaccuracies can be compensated.

[00128] For standardization, the measurement signal of strain gauge 40 is recorded and standardized in the unloaded resting state. This standardization step is typically performed only once at the beginning of the measurements.

[00129] The standardized zero value signal 82c thus obtained is used to calibrate an output signal 82d, which is amplified in a further signal amplifier 116 to a standardized digital signal 83. Since this signal 83 can also assume negative voltage values if the respective strain gauge 40 or the associated piston 10 is, for example, not subjected to compression but to extension and records tensile forces, the signal 83 in the

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Device 117 for signal value normalization including signal value adjustment using signal offset by combining it with an offset signal 84 raises the signal and obtains a processed output signal 85. To protect the measuring sensors and measuring electronics, a first voltage limiter 118 upstream of the D/A converter 119 serves to limit the voltage, for example, to a maximum of 10 V. A correspondingly limited output signal 86 is converted in the D/A converter 119 into an analog signal 87, which, after passing through a second voltage limiter 120, is output as a voltage signal 121 by the measurement data acquisition unit 110.

[00130] Fig. 13 shows a diagram of the voltage curve of a measurement signal over time. The time t in milliseconds [ms] is plotted on the abscissa. The voltage U in volts [V] is plotted on the ordinate. In the ordinate direction, a voltage amplitude A is also shown as arrow A. The voltage curve shown results from a sequence of recorded voltage peaks of a strain gauge during the tooth engagement of the respective piston equipped with the respective strain gauge. The index 1 designates the first tooth engagement, the index 2 designates the second tooth engagement, and so on. Starting from the left, a comparatively low voltage peak E1 can be observed at the beginning of the first tooth engagement, followed by a maximum voltage peak S1 at the highest load during the first tooth engagement, and followed by a again lower voltage peak L1 upon release of the first tooth engagement. These signals repeat in a periodic sequence, essentially with each subsequent tooth engagement. During the second tooth engagement, a signal sequence is again recorded: a comparatively low voltage peak E2 at the beginning of the second tooth engagement, followed by a maximum voltage peak S; at the highest load during the second tooth engagement, and followed by a again lower voltage peak L2 when the second tooth engagement is released.

[00131] A period P can be determined as the time interval t2-t1 between two corresponding voltage peaks S+4,$; at the highest load during the tooth engagement, or between two corresponding voltage peaks E41,E2 at the beginning of the tooth engagement, or between two corresponding voltage peaks L4,L2 when the tooth engagement is released.

[00132] Furthermore, Fig. 13 illustrates an increase in the recorded voltage signals as a signal drift toward higher voltage values with a slope S = Ay/Ax. The slope S provides information about the relative temperature change. As the temperature increases, the signal drifts toward higher voltage values.

[00133] With reference to the figures, in particular to Fig. 13, the functioning of the invention is explained below on the basis of the determination of the rotational speed, the rotational angle position, the torque and the determination of a temperature change during the measurement of resistance signals of the strain gauges 40.

[00134] In addition, the determination of the direction of rotation is also explained using two strain gauges 40, which are attached to spaced-apart pistons 10a, 10b.

FUNCTION OF THE INVENTION A) Determination of the rotational speed

[00135] With the system according to the invention, the rotational speed of the hollow shaft 30 or the guide unit 8 can be determined, wherein the evaluation device 100 is configured to determine at least one actual value signal of a current rotational speed, wherein the determination comprises the following steps:

- detecting and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of the coaxial gear 1;

- Determining a period P as a time interval t2-t1 between two corresponding voltage peaks S1,S2; E1,E2; L1,L2 of the voltage signal 121 of the respective strain gauge 40;

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- Conversion of the period P taking into account the number L of gaps 32 of the internal gearing 31 of the hollow shaft 30 into a current rotational speed w=(27/L)/P.

[00136] In order to determine the current rotational speed @ of the hollow shaft 30 or the guide unit 8 of the coaxial gear 1, the period P is evaluated as the time interval t2-t1 between two corresponding voltage peaks of the voltage signal of the respective strain gauge.

[00137] The angle of rotation ®=27/L corresponding to a period P. [00138] The rotational speed = ®/P=(27/L)/P is given in [rad/s].

[00139] To determine the rotational speed, the period P is also evaluated as the time interval between two corresponding voltage peaks S4,S2; E1,E2; L1,L2 of the voltage signal of the respective strain gauge 40. The period P is directly proportional to the rotational speed.

B) Determination of the angle of rotation

[00140] The system according to the invention can determine the current angular position of the hollow shaft 30 or the guide unit 8. The evaluation device 100 is configured to determine at least one actual value signal of a current angular position, wherein the determination comprises the following steps:

- detecting and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of the coaxial gear 1;

- Determining the respective times t1, t2 of voltage peaks S+, S2; E1, E2; L1, L2z of the respective strain gauge 40;

- Assigning the respective times t1, t2 of stress peaks S+4, S2; E1, E2; L1, L2z taking into account the number L of gaps 32 of the internal gearing 31 of the hollow shaft 30 as an increment of a current rotational angle position of the respective strain gauge 40.

[00141] If the times t4, t2,..., tn are corresponding stress peaks, then n is the number of periods P or gaps L or recesses in the internal toothing into which the respective piston has engaged. In the time interval from time t0=0 to time t, the hollow shaft 30 or the guide unit 8 of the coaxial gear i has therefore rotated further by a differential angle of rotation A®=n-27/L.

[00142] The current angle of rotation position is then ®=®,+A®, where %, is a known angle of rotation at time t0=0.

C) Determination of the torque

[00143] The system according to the invention can also determine the current torque of the coaxial transmission 1. The evaluation device 100 is configured to determine at least one actual value signal of a current torque, wherein the determination comprises the following steps:

- detecting and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of the coaxial gear 1;

- Calibrating the at least one strain gauge 40, preferably all strain gauges 40, at predefined torques and assigning the respective voltage amplitudes U4,U2 of voltage peaks S+,S2; E1,E2; L1,L2 of the respective strain gauge 40 to a calibrated torque value;

- Comparing the respective current voltage amplitudes U1,U2 of voltage peaks S1, S2; E4,Ez2; L1,L2 of the respective strain gauge 40 during operation of the capacitor

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axial gear 1 with the calibrated torque values and determining a current torque.

[00144] The step of calibrating the at least one strain gauge 40 or all strain gauges 40 is generally to be carried out only once at the beginning of the measurements.

D) Determination of temperature change

[00145] The system according to the invention can also be used to determine a current temperature within the coaxial transmission 1 or at the location of the relevant strain gauge 40. For this purpose, the evaluation device 100 is configured to determine at least one actual value signal of a current temperature, wherein the determination comprises the following steps:

- detecting and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of the coaxial gear 1;

- Calibrating the at least one strain gauge 40, preferably all strain gauges 40, at predefined temperatures and assigning an offset of the respective voltage signal 121 of the respective strain gauge 40 to a known temperature value prevailing during calibration;

- Determining corresponding voltage peaks S+4,S2;; E1,E2; L1,L2z of the voltage signal 121 of the respective strain gauge 40 over time and determining the slope S of a signal drift;

- Calculation of a relative temperature change AT by multiplying S by a corresponding known material constant of the strain gauge 40 in question;

- determining an initial temperature To based on the offset of the voltage signal 121 in an initial time range;

- Determine the current temperature T by adding To and AT.

[00146] The slope S of the signal drift provides information about the relative temperature change. As the operating temperature increases, the voltage signal moves toward higher voltage values. The signal range (e.g., 0-10 V) must therefore lie within the temperature range expected during operation of the coaxial gear. The characteristic of the temperature behavior of the strain gauge in question can be determined from its temperature coefficient (Temp. of Gauge Factor), i.e., a material constant according to the strain gauge data sheet. This allows the measuring range of the voltage signals to be adjusted according to the expected temperature range during operation of the coaxial gear.

E) Determination of the direction of rotation

[00147] With the system according to the invention, the direction of rotation of the hollow shaft 30 or of the guide unit 8 can also be determined, wherein the evaluation device 100 is configured to determine at least one actual value signal of a current direction of rotation, wherein the determination comprises the following steps:

- detecting and evaluating at least one first voltage signal 81a, 121 of a first strain gauge 40, 41a arranged on a first piston 10a, and at least one second voltage signal 81b, 121 of a second strain gauge 40, 41b arranged on a second piston 10b spaced from the first piston 10a, during operation of the coaxial transmission 1;

- Determining at least one time t1 of the incoming first voltage signal 81a, 121, and at least one time t2 of the incoming second voltage signal 81b, 121, preferably taking into account the respective corresponding voltage peaks

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S1,S2; E41,E2; L1,L2 of the first voltage signal 81a,121 of the respective first strain gauge 40,41a and of the second voltage signal 81b,121 of the respective second strain gauge 40,41b;

- Determining the temporal sequence t+-t2; t2-t1 of a signal sequence of the first voltage signal 81a, 121 of the respective first strain gauge 40, 41a and of the second voltage signal 81b, 121 of the respective second strain gauge 40, 41b.

[00148] The index 1 denotes the time t1 of the incoming first voltage signal 81a, 121 of the first strain gauge 40, 41a under consideration on the first piston 10a. The index 2 denotes the time t2 of the incoming second voltage signal 81b, 121 of the second strain gauge 40, 41b under consideration on the second piston 10b.

[00149] To determine the direction of rotation, the sequence of the incoming voltage signals from at least two strain gauges 40 and 41a, 41b, respectively, attached to different pistons 10a, 10b, must be evaluated. In this case, the corresponding voltage peaks S+, S2; E1, E2; L1, L2 of the incoming voltage signals 81a, 81b, 121 must also be taken into account.

[00150] For example, a temporal sequence t1-t2 of the signal sequence of the incoming voltage signals 81a, 121 of the first strain gauge 40, 41a first at the first piston 10a and with a time delay to the later arriving voltage signals 81b, 121 of the second strain gauge 40, 41b at the second piston 10b is opposite in direction of rotation to a temporal sequence t2-t1 of the signal sequence of the incoming voltage signals 81b, 121 of the second strain gauge 40, 41b first at the second piston 10b and then or with a time delay to the later arriving voltage signals 81a, 121 of the first strain gauge 40, 41a at the first piston 10a.

[00151] By appropriately determining the temporal sequence of the incoming voltage signals to a first direction of rotation, a second direction of rotation opposite to the first direction of rotation and thus the respective current direction of rotation can also be determined.

LIST OF REFERENCE SYMBOLS

1 coaxial gearbox

2 axis of rotation

3 piston drive

3a Crankshaft

4 Connecting rod bearings; connecting rod journal; crank pin 5 Piston set

6 Connecting rods (or 6a, 6a', 6b, 6b', 6c, 6c') 7 Circumferential direction (double arrow)

8 Guide unit

9 Guide bridge

10 pistons (or 10a-10p)

11 first end face of the piston

12 Gearing

13 tooth

13a first tooth flank

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x bes AT 527 841 B1 2025-07-15

Ss N

LIST OF REFERENCE SYMBOLS (continued)

13b second tooth flank

13c tooth width

13d Orientation direction of the tooth (double arrow) 13e Tooth height

14 Piston longitudinal axis

15 Radial direction (double arrow)

16 Bore for piston pin

17 Longitudinal axis direction of the piston pin bore 18 First piston segment

18a Chamfer width of the first piston segment

19 second piston segment

19a Chamfer width of the second piston segment

20 Recess for connecting rod connection

21 Piston pin; coupling pin

22 intermediate link

23 guide bolts

25 connecting bolts

27 Swivel joint

29 web recess

29a Width of the web recess

30 hollow shaft

31 Internal toothing of the hollow shaft

32 Gap or recess of the internal gearing 40 Strain gauges; DMS

40a Width of the strain gauge; DMS

41 Foil strain gauges; foil strain gauges (or 41a-41h) 42 Semiconductor strain gauges; semiconductor strain gauges 60 Star-shaped connecting rod

70 Wheatstone bridge

71 first resistance

72 second resistance

73 third resistance

74 fourth resistance

80 applied voltage

81 Diagonal voltage

81a,81b Diagonal voltage of a single strain gauge

82 increased (increased) voltage

82a Raw signal

82b normalized signal

x bes AT 527 841 B1 2025-07-15

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LIST OF REFERENCE SYMBOLS (continued)

82Cc normalized zero value signal

82d output signal

83 standardized digital signal

84 Offset signal

85 processed output signal

86 limited output signal

87 analog signal

90 Signal line for resistance change; connection cable 100 Evaluation device for measured data

110 Measurement data acquisition unit

111 Bridge circuit

112 (first) measuring amplifier

113 A/D converters

114 Signal value normalization

115 Zero value normalization

116 (second) measuring amplifier; signal value amplifier 117 signal offset

118 voltage limiters

119 D/A converters

120 voltage limiters

121 Output voltage signal

130 Measurement data analysis unit

131 CPU-processor

132 RAM

135 Data storage facility

136 configuration data storage

138 signal converters; 1/O-Link

140 Actual value signal

150 PLC control device

160 external data monitoring device

A Amplitude

E1,E2 Stress peak at the beginning of the meshing L41,L2 Stress peak when releasing the meshing P Period

S1,S2,S3 Stress peak at highest load during tooth meshing t41,t2,t3 time

Claims (1)

x bes AT 527 841 B1 2025-07-15 Ss N Patent claims 1. Coaxial gearbox (1), comprising: - at least one piston set (5) with at least three pistons (10a-10p), wherein the pistons (10a-10p) each have a toothing (12) with at least one tooth (13) on a first end face (11) facing away from a rotational axis (2); - a hollow shaft (30) with an internal toothing (31), wherein the pistons (10a-10p) are arranged within the hollow shaft (30) when viewed in a plane normal to the axis of rotation (2); - a guide unit (8), wherein the pistons (10a-10p) of the respective piston set (5) are each arranged in the guide unit (8) at a distance from one another by guide webs (9) in a circumferential direction (7) pointing around the axis of rotation (2), and are linearly guided and can be moved back and forth parallel to a radial direction (15) normal to the axis of rotation (2); - a piston drive (3) for the linear guided movement of the pistons (10a-10p), - wherein the toothings (12, 13) of the first end faces (11) of the pistons (10a-10p), in particular one after the other, can be brought into engagement with the internal toothing (31) and into a state detached from the internal toothing (31) in order to continue rotating the hollow shaft (30) or the guide unit (9) about the axis of rotation (2) during the respective engagement, preferably with surface contact between the respective toothing (12, 13) and the internal toothing (31), characterized in that on at least one of the pistons (10a, 10c, 10e, 110g, 10i, 10k, 10m, 100) at least one expansion voltage measuring strips (40,41,42) are attached. 2. Coaxial transmission (1) according to claim 1, characterized in that at least one strain gauge (40, 41, 42) is fastened to at least three pistons (10a, 10c, 10e, 10g, 10i, 10k, 10m, 100), which are preferably arranged in a circumferential direction (7), particularly preferably uniformly, distributed. 3. Coaxial transmission (1) according to claim 1 or 2, characterized in that the at least one piston set (5) comprises an even number of at least six pistons (10a-10p), wherein at least one strain gauge (40, 41, 42) is attached to at least every second piston (10a, 10c, 10e, 10g, 10i, 10k, 10m, 100). 4. Coaxial transmission (1) according to one of claims 1 to 3, characterized in that at least one strain gauge (40, 41, 42) is attached to each piston (10a-10p). 5. Coaxial transmission (1) according to one of claims 1 to 4, characterized in that the at least one strain gauge (40, 41, 42) is arranged in a first piston segment (18) on the respective piston (10a-10p), wherein the first piston segment (18) forms an outer surface section on the respective piston (10a-10p) and is positioned in the radial direction (15) parallel to a piston longitudinal axis (14) and at least in sections normal to an orientation direction (13d) of the at least one tooth (13) of the respective piston (10a-10p). 6. Coaxial transmission (1) according to one of claims 1 to 5, characterized in that at least two strain gauges (40, 41, 42) are fastened to at least one, preferably to at least three pistons (10a, 10c, 10e, 10g, 10i, 10k, 10m, 100) arranged distributed in the circumferential direction (7). 7. Coaxial transmission (1) according to claim 6, characterized in that a first strain gauge (40, 41, 42) in a first piston segment (18) and a second strain gauge (40, 41, 42) in a second piston segment (19) opposite the first piston segment (18) are arranged on the same piston (10a-10p), wherein the first piston segment (18) and the second piston segment (19) each form an outer surface section on the respective piston (10a-10p) and each in the radial direction 10. 11. 12. 13. AT 527 841 B1 2025-07-15 (15) are positioned parallel to a piston longitudinal axis (14) and at least partially normal to an orientation direction (13d) of the at least one tooth (13) of the respective piston (10a-10p). Coaxial transmission (1) according to one of claims 5 to 7, characterized in that a first piston segment (18) and/or a second piston segment (19) is/are each formed as a chamfered outer surface section on the respective piston (10a-10p), wherein preferably a chamfer width (18a) of the first piston segment (18) and/or a chamfer width (19a) of the second piston segment (19) is/are each greater than or equal to a width (40a) of a strain gauge (40, 41, 42). Coaxial transmission (1) according to one of claims 5 to 8, characterized in that a web recess (29) is arranged on the respectively adjacent guide web (9) of the guide unit (8) corresponding to the position of a first piston segment (18) and/or corresponding to the position of a second piston segment (19) of the respective piston (10a-10p), wherein the respective web recess (29) runs in the radial direction (15) parallel to the piston longitudinal axis (14) of the respective piston (10a-10p) and the at least one strain gauge (40, 41, 42) is arranged at least in sections in the web recess (29), wherein the respective web recess (29) preferably has a recess width (29a), which recess width (29a) is greater than or equal to a width (40a) of a strain gauge (40, 41, 42). Coaxial transmission (1) according to one of claims 1 to 9, characterized in that the at least one strain gauge (40) is selected from the group comprising: foil strain gauges (41), semiconductor strain gauges (42), rosette strain gauges, wire strain gauges. Coaxial transmission (1) according to one of claims 1 to 10, characterized in that the piston drive (3) comprises a crankshaft (3a) rotatable about the axis of rotation (2) with at least one connecting rod bearing (4), wherein at least one connecting rod (6) is provided, which connecting rod (6) is coupled to one or more pistons (10a-10p) of the at least one piston set (5) and to the at least one connecting rod bearing (4). Coaxial transmission (1) according to claim 11, characterized in that for connecting the pistons (10a-10p) of the respective piston set (5) to the at least one connecting rod bearing (4), a common, star-shaped connecting rod (60) is provided, to which the pistons (10a-10p) of the respective piston set (5) are coupled, or that a separate connecting rod (61a-61p) is provided for connecting each piston (10a-10p) of the respective piston set (5) to the at least one connecting rod bearing (4). System comprising a coaxial gear (1) according to one of claims 1 to 12 and a Evaluation device (100) for the acquisition and evaluation of measurement data, wherein - the evaluation device (100) comprises a measurement data acquisition unit (110) and a measurement data analysis unit (130), wherein - the measurement data acquisition unit (110) is signal-connected (90) to the at least one, preferably at least three, particularly preferably all, strain gauges (40, 41a, 41h, 42) of the coaxial transmission (1), and the measurement data acquisition unit (110) is configured to detect resistance changes of each of the strain gauges (40, 41a- 41h) by means of at least one bridge circuit (111) and outputs corresponding voltage signals (121), and wherein - the measurement data analysis unit (130) is configured to determine at least one actual value signal (140) of a current rotational speed and/or a current rotational angle position and/or rotational direction and/or a current torque and/or a current temperature and/or a currently acting force on the basis of the voltage signals (121) output by the measurement data acquisition unit (110) of each of the strain gauges (40, 41a-41h, 42), and preferably to output said actual value signal to a control device (150) and/or to an external data monitoring device (160). 24 1 32 x bes AT 527 841 B1 2025-07-15 Ss N 14. A method for determining a current rotational speed using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current rotational speed, comprising the following steps: - detecting and evaluating the voltage signals (121) of at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), during operation of the coaxial gear (1); - determining a period P as a time interval (t2 - t1ı) between two corresponding voltage peaks (S4,S2; E1,E2; L1,L2) of the voltage signal (121) of the respective strain gauge (40,41,42); - Convert the period P taking into account the number L of gaps in the internal gearing (31) of the hollow shaft (30) into a current rotational speed © = (2L)/P. 15. A method for determining a current rotational angle position using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current rotational angle position, comprising the following steps: - detecting and evaluating the voltage signals (121) of at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), during operation of the coaxial gear (1); - determining the respective times (t1,t2) of voltage peaks (S4,S2; E1,E2; L1,L2) of the respective strain gauge (40,41,42); - Assigning the respective times (t1,t2) of stress peaks (S4,S2; E1,E2; L4,L2) taking into account the number L of gaps in the internal toothing (31) of the hollow shaft (30) as an increment of a current angular position of the respective strain gauge (40,41,42). 16. A method for determining a current torque using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current torque, comprising the following steps: - detecting and evaluating the voltage signals (121) of at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), during operation of the coaxial gear (1); - Calibrating the at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), at predefined torques and assigning the respective voltage amplitudes (U+4,U2) of voltage peaks (S4,S2; E41,Ez2; L1,L2) of the respective strain gauge (40,41,42) to a calibrated torque value; - Comparing the respective current voltage amplitudes (U+4,U2) of voltage peaks (S4,S2; E1,E2; L1,L2) of the respective strain gauge (40,41,42) during operation of the coaxial gear (1) with the calibrated torque values and determining a current torque. 17. A method for determining a current temperature using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current temperature, comprising the following steps: - detecting and evaluating the voltage signals (121) of at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), during operation of the coaxial gear (1); - Calibrating the at least one strain gauge (40, 41, 42), preferably all strain gauges (40, 41, 42), at predefined temperatures and assigning an offset of the respective voltage signal (121) of the respective strain gauge 25 / 32 strip (40,41,42) to a known temperature value prevailing during calibration; - determining corresponding voltage peaks (S41,S2; E1,E2; L1,L2) of the voltage signal (121) of the respective strain gauge (40,41,42) over time (t) and determining the slope S of a signal drift; - Calculation of a relative temperature change AT by multiplying S by a corresponding known material constant of the strain gauge in question (40,41,42); - determining an initial temperature To based on the offset of the voltage signal (121) in an initial time range; - Determine the current temperature T by adding To and AT. 6 sheets of drawings 26 / 32