HK1170562B - Apparatus for absolute position sensing - Google Patents

Abstract

To determine the relative position of movable portions of an assembly, a first magnetic device is coupled to a first portion of the assembly. The first magnetic device has a sensing surface with a number of magnetic poles that provide a magnetization state transition location. An absolute position sensor with a two-state output is coupled to the assembly adjacent the first magnetic device. The output state changes when a magnetization state transition of the first magnetic device moves past the absolute position sensor. A second magnetic device is coupled to the assembly. The second magnetic device creates a cyclically-varying magnetic field proximate its sensing surface. An incremental position sensor is coupled to the assembly adjacent the second magnetic device, and has an output that varies continuously relative to magnetic field angle over at least a portion of one cycle of the cyclically-varying magnetic field of the second magnetic device.

Description

Absolute position sensing device

Technical Field

The present disclosure relates to position sensing.

Background

There are many of the following situations: it is desirable to sense the position of one or more relatively movable portions of the assembly (assembly). One example is a machine tool in which a movable member such as a tool needs to be accurately positioned relative to a fixed member such as a workpiece or table. Other examples include active suspension (suspension) systems for vehicles or portions of vehicles that are subject to random accelerations, particularly when the vehicle is moving. For an active suspension system to be effective, the position of the movable portion of the assembly must be known.

Disclosure of Invention

In general, in one aspect, the invention provides an apparatus that includes a linear motor including a stator and an armature movable relative to the stator over a stroke distance. A first magnetic device is coupled to the armature. The first magnetic device defines a sensing surface that includes a plurality of magnetic poles that provide magnetization state transition locations therebetween. A pole sensor is coupled to the stator adjacent the first magnetic device such that as the armature moves relative to the stator over the travel distance, the first magnetic device moves past the pole sensor, which senses the adjacent poles of the first magnetic device. A second magnetic device is coupled to the armature, the second magnetic device defining a sensing surface comprising a plurality of adjacent alternating opposite magnetic poles that create a cyclically varying magnetic field proximate the sensing surface thereof. A magnetic field angle sensor is coupled to the stator adjacent the second magnetic device such that as the armature moves relative to the stator, the cyclically varying magnetic field of the second magnetic device moves past the magnetic field angle sensor, the magnetic field angle sensor sensing the angle of the magnetic field of the second magnetic device and having a value that varies during the cycle

Various embodiments of the invention may include one or more of the following features. The pole sensor may comprise a single hall sensor. The magnetic field angle sensor may comprise a magnetoresistive sensor. The magnetic field angle sensor may comprise a bipolar hall sensor and may have a full-range output of 180 ° such that its output repeats twice for each magnetic field cycle of the second magnetic device. The first magnetic device may be at least half as long as the stroke distance of the armature, and the second magnetic device may be at least as long as the stroke distance of the armature.

Various other implementations may include one or more of the following features. Adjacent poles of the second magnetic device may meet at a magnetization state transition location, and the first and second magnetic devices may be coupled to the armature such that a known and defined spatial relationship exists between the magnetization state transition location of the first magnetic device and at least one magnetization state transition location of the second magnetic device. The transition position of the first magnetic device may be approximately centered with respect to a length of a sensing surface of the second magnetic device. The magnetic field angle sensor output may be reset at least one location on each magnetic field cycle, and the first and second magnetic devices may be arranged such that when the magnetic pole sensor is adjacent to the transition location of the first magnetic device, the magnetic field angle sensor is not adjacent to the location at which it is reset. The apparatus may further comprise a third magnetic device coupled to the armature adjacent to the first magnetic device, the third magnetic device defining a sensing surface that defines a single magnetization state transition location over an armature travel distance, wherein the sensing surfaces of the first and third magnetic devices each comprise at least two magnetic poles, and wherein adjacent magnetic poles of the first and third magnetic devices have opposite polarities.

In general, in another aspect, the invention provides an apparatus comprising a linear motor comprising a stator and an armature movable relative to the stator over a stroke distance; a first magnetic device coupled to the armature, the first magnetic device defining a sensing surface comprising a plurality of magnetic poles providing magnetization state transition locations therebetween; a pole sensor coupled to the stator adjacent the first magnetic device such that the first magnetic device moves past the pole sensor as the armature moves relative to the stator over the travel distance, the pole sensor sensing an adjacent pole of the first magnetic device. There is a second magnetic device coupled to the armature, the second magnetic device defining a sensing surface that is at least as long as the travel distance of the armature and that includes a plurality of adjacent alternating opposite magnetic poles that create a cyclically-varying magnetic field near its sensing surface. A magnetic field angle sensor is coupled to the stator adjacent the second magnetic device such that as the armature moves relative to the stator, the cyclically varying magnetic field of the second magnetic device moves past the magnetic field angle sensor, the magnetic field angle sensor sensing the angle of the magnetic field of the second magnetic device and having an output that varies continuously with respect to the magnetic field angle over at least a portion of one cycle of the cyclically varying magnetic field. Adjacent poles of the second magnetic device meet at a magnetization state transition location, and the first and second magnetic devices are coupled to an armature such that a known and defined spatial relationship exists between the magnetization state transition location of the first magnetic device and at least one magnetization state transition location of the second magnetic device. The magnetic field angle sensor output resets at one or two locations on each magnetic field cycle, and the first and second magnetic devices are arranged such that when the magnetic pole sensor is adjacent to the transition location of the first magnetic device, the magnetic field angle sensor is not adjacent to the location at which it resets.

In general, in another aspect, the invention provides a sensing system for determining the position of one or more relatively movable portions of an assembly that move over a travel distance. The sensing system includes a first magnetic device coupled to a first portion of the assembly, the first magnetic device defining a sensing surface including a plurality of magnetic poles that provide magnetization state transition locations therebetween. The sensing system further includes an absolute position sensor coupled to a second portion of the stator assembly adjacent the first magnetic device and having a two-state output, wherein the output state changes as the magnetization state transition of the first magnetic device moves past the absolute position sensor as the portions move relative to each other over the travel distance. There is a second magnetic device coupled to the first portion of the assembly, the second magnetic device creating a cyclically varying magnetic field in the vicinity of its sensing surface. An incremental position sensor is coupled to a second portion of the assembly adjacent the second magnetic device and has an output that repeats at least once for each cycle of the cyclically-varying magnetic field of the second magnetic device.

Various embodiments of the invention may include one or more of the following features. The absolute position sensor may comprise a hall sensor. The incremental position sensor can include a magnetic field angle sensor coupled to a second portion of the assembly such that as the cyclically-varying magnetic field of the second magnetic device moves past the magnetic field angle sensor, the magnetic field angle sensor senses the angle of the magnetic field of the second magnetic device and has an output that varies continuously in relation to the magnetic field angle over at least a portion of one cycle of the cyclically-varying magnetic field. The second magnetic device may define a sensing surface comprising a plurality of adjacent alternating opposite magnetic poles creating a cyclically varying magnetic field in the vicinity of its sensing surface. The magnetic pole sensor may comprise a bipolar hall sensor and the magnetic field angle sensor may have a full range output of 180 ° such that its output repeats twice for each magnetic field cycle of the second magnetic device. The first magnetic device may be at least half as long as the travel distance and the second magnetic device may be at least as long as the travel distance.

Various other implementations may include one or more of the following features. Adjacent poles of the second magnetic device may meet at a magnetization state transition location, and the first and second magnetic devices may be coupled side-by-side to the armature such that a known and defined spatial relationship exists between the magnetization state transition location of the first magnetic device and the adjacent magnetization state transition location of the second magnetic device. The transition position of the first magnetic device may be approximately centered with respect to a length of a sensing surface of the second magnetic device. The magnetic field angle sensor output may be reset at least one location on each magnetic field cycle, and the first and second magnetic devices may be arranged such that when the hall sensor is adjacent to the transition location of the first magnetic device, the magnetic field angle sensor is not adjacent to the location at which it is reset. The sensor system may further include a third magnetic device coupled to the first portion of the assembly alongside the first magnetic device, the third magnetic device defining a sensing surface that defines a single magnetization state transition location over the travel distance, wherein the sensing surfaces of the first and third magnetic devices each include at least two magnetic poles, and wherein adjacent magnetic poles of the first and third magnetic devices have opposite polarities.

In general, in another aspect, the invention provides a control system that controls one or more actuators that move relatively movable portions of an assembly, thereby controlling the position of the portions of the assembly. The control system includes an absolute position sensor having a two-state output, one state indicating a first portion of the relative movement and the other state indicating a second, different portion of the relative movement. There is an incremental position sensor having an output that varies continuously over at least a portion of each of a plurality of repeating cycles associated with the relative movement; and a controller that receives the outputs of the two sensors. Upon activation, at least one of the portions of the assembly moves until the absolute position sensor changes state, and in response, the controller determines an absolute position of the portion of the assembly.

Various embodiments of the invention may include one or more of the following features. The controller may track information indicative of a cycle currently being sensed by the incremental position sensor, and after startup, the controller may determine an absolute position of at least one of the portions of the assembly based on both an identification of which cycle is currently being sensed by the incremental position sensor, and an output of the incremental position sensor, upon relative movement of the portions of the assembly. Upon startup, the controller may determine an absolute position of the portion of the assembly based at least in part on an identification of which of the plurality of cycles is currently being sensed by the incremental position sensor. The total number of cycles may be fixed, and the controller may detect an error if the number of cycles tracked exceeds a predetermined number of cycles. The absolute position sensor can be used to confirm correct tracking of the cycle. The sensor may be a non-contact sensor. The absolute position sensor may comprise a hall sensor and the incremental position sensor may comprise a magnetoresistive sensor.

In general, in another aspect, the invention provides a method of operating a control system that controls one or more actuators that move one or more relatively movable portions of an assembly, thereby controlling the position of the portions of the assembly. The control system includes an absolute position sensor having a two-state output, one state indicating a first portion of relative movement of the portions of the assembly and the other state indicating a second, different portion of the relative movement. There is an incremental position sensor having an output that varies continuously over at least a portion of each of a plurality of repeating cycles associated with the relative movement; and a controller that receives outputs of the two sensors and outputs a control signal. The controller outputs a signal that causes at least a portion of the assembly to move until a state of the absolute position sensor changes, and determines an absolute position of at least one of the portions of the assembly based at least on an output of the incremental position sensor.

Various embodiments of the invention may include one or more of the following features. The controller may track information indicative of a cycle currently being sensed by the incremental position sensor, and upon relative movement of the portions of the assembly the controller may determine an absolute position of at least one of the portions of the assembly based on both the identification of which cycle is currently being sensed, and the output of the incremental position sensor. The total number of cycles may be fixed, and the controller may detect an error if the number of cycles tracked exceeds a predetermined number of cycles. An absolute position sensor may be used to confirm proper tracking of the cycle.

In general, in another aspect, the invention provides a positioning system for positioning a movable portion of an assembly relative to another portion of the assembly. The positioning system includes an electromagnetic motor including a stator and an armature coupled to a movable portion of the assembly and movable relative to the stator over a stroke distance. A single phase actuator is coupled to the movable portion of the assembly. A first magnetic device is coupled to the armature, the first magnetic device defining a sensing surface including a plurality of magnetic poles that provide magnetization state transition locations therebetween. A pole sensor having a two-state output is coupled to the stator adjacent the first magnetic device such that the first magnetic device moves past the pole sensor as the armature moves relative to the stator over the travel distance. One state of the magnetic pole sensor output indicates a first portion of the relative movement and another state indicates a second, different portion of the relative movement. A second magnetic device is coupled to the armature, the second magnetic device defining a sensing surface comprising a plurality of adjacent alternating opposite magnetic poles that create a cyclically varying magnetic field proximate the sensing surface thereof. A magnetic field angle sensor is coupled to the stator adjacent the second magnetic device such that as the armature moves relative to the stator, the cyclically-varying magnetic field of the second magnetic device moves past the magnetic field angle sensor, the magnetic field angle sensor sensing an angle of the magnetic field of the second magnetic device and having an output that varies continuously with respect to the magnetic field angle over at least a portion of each of a plurality of cycles of the cyclically-varying magnetic field. A controller is responsive to the two sensors to control the single phase actuator to move the movable portion of the assembly until the output of the pole sensor changes state. In response to the state change, the controller determines an absolute position of at least one of the portions of the assembly.

Various embodiments of the invention may include one or more of the following features. The electromagnetic motor may comprise a linear multi-phase electromagnetic motor, and the single-phase actuator may comprise a pneumatic cylinder. The controller may track information indicative of a cycle currently being sensed by the magnetic field angle sensor, and upon relative movement of the portions of the assembly the controller may determine an absolute position of at least one of the portions of the assembly based on both an identification of which of the plurality of cycles is currently being sensed by the magnetic field angle sensor, and an output of the magnetic field angle sensor. The magnetic pole sensor may comprise a hall sensor and the magnetic field angle sensor may comprise a magnetoresistive sensor. The movable portion may comprise a seat in a motor vehicle.

Drawings

FIG. 1 is a schematic diagram of a position control system utilizing position sensing in accordance with the present invention;

FIG. 2 is a perspective view of a linear motor incorporating an embodiment of the present invention;

FIG. 3A is a perspective view of a portion of the system shown in FIG. 2, illustrating in detail an embodiment of a magnetic device for use in embodiments of the present invention;

FIG. 3B is a similar view showing additional embodiments of magnetic devices for use with embodiments of the present invention, and also showing in detail absolute position sensors and incremental position sensors for use with embodiments of the present invention;

FIG. 4A is a schematic side view of a magnetic device for use in an embodiment of the present invention, illustrating its magnetic field lines near its sensing surface;

FIG. 4B is a graph showing the magnetic field components thereof relative to position along the x-axis;

FIG. 4C is a graph showing the output of an incremental position sensor for use in embodiments of the present invention in relation to the position of the incremental position sensor relative to the x-axis of the magnetic device of FIG. 4A;

FIGS. 5A and 5B illustrate the output of the sensor shown in FIG. 3B as it moves relative to the magnetic field device shown in FIG. 3B;

FIG. 6 is a more detailed view of a portion of the graph of FIG. 4C useful in explaining embodiments of the present invention;

FIG. 7A is a flow chart illustrating startup of a control system using one embodiment of the present invention;

FIG. 7B is a flow chart illustrating operation of a control system using one embodiment of the present invention;

FIG. 8 illustrates an actively suspended seat; and

FIG. 9 is a schematic block diagram of a positioning system for use with embodiments of the present invention.

Detailed Description

The present invention may be implemented in a position sensing system and method for determining the position of one or more relatively movable portions of an assembly that move over a travel distance. A first magnetic device is coupled to the first portion of the assembly. The term "coupled" as used herein may mean either a direct mechanical coupling (in this case, a first magnetic device to the first portion of the assembly) or an indirect mechanical coupling (such as may be achieved with one or more other devices, structures, or components located between the magnetic device and the first portion of the assembly) of two devices, structures, or components. The first magnetic device has a sensing surface defining one or more magnetization state transition locations over a travel distance. One or more absolute position sensors are coupled to the second portion of the assembly adjacent the first magnetic device. The absolute position sensor preferably has a two-state output, wherein the output state changes when the magnetization state transition of the first magnetic device moves past the absolute position sensor as the portions move relative to each other over the travel distance. A second magnetic device is coupled to the first portion of the assembly. The second magnetic device creates a cyclically varying magnetic field in the vicinity of its sensing surface. An incremental position sensor is coupled to a second portion of the assembly adjacent the second magnetic device and has an output that repeats in direct correlation to the cycle of the second magnetic device. For example, the output of the incremental position sensor may be repeated once for each cycle of the second magnetic device, or may be repeated twice for each cycle of the second magnetic device. The output of the incremental position sensor may be continuously varied in relation to the magnetic field angle at each repetition of its output, so that the position with respect to each cycle may be determined via the output of the incremental position sensor. The term "continuously" as used herein in relation to the output of the incremental position sensor means that the output is a continuous function of the sensed magnetic field angle over a sensor output range, which in embodiments is 180 ° or 360 °. Typically, the incremental position sensor output varies monotonically over its output range and resets an integer number of times per cycle of the cyclically varying magnetic field.

FIG. 1 shows an assembly 10 having portions 12 and 14. One or both of the sections 12 and 14 may be moved relative to each other to achieve a desired relative position between the sections 12 and 14. In the example shown, the portion 14 is laterally movable back and forth in the direction of arrow 16, and the portion 12 is stationary. The invention is useful in assemblies comprising two or more parts, any one or more of which may be movable relative to any one or more of the other parts.

The assembly 10 further includes sensors 18 and 20, the outputs of the sensors 18 and 20 being provided to a controller 24. The output of controller 24 is provided to mover 26 which moves portion 14 relative to portion 12. Mover 26 may include one or more devices known in the art, such as an actuator. The movers may be single phase or multiphase devices.

One of the sensors 18 and 20 is an absolute position sensor having a two-state output. One state indicates a first portion of the relative movement of portions 12 and 14 and the other state indicates a second, different portion of the relative movement. The other of the sensors 18 and 20 is an incremental position sensor having an output that varies continuously over at least part of each of a number of discrete cycles over both the first and second portions of relative movement. In the embodiment described herein, the sensors 18 and 20 are non-contact sensors. In the embodiment described herein, sensors 18 and 20 are magnetic sensors that sense aspects of one or more magnetic devices represented by magnetic device 22 located on portion 14 adjacent to sensors 18 and 20.

Fig. 2 depicts a linear motor 50 having a stator 52 and an armature 54. This is one example of an assembly that may be used with the present invention. The armature 54 defines a series of poles 56. The armature 54 moves in and out relative to the stator 52 in the direction of arrow 55; the operation of linear motors is well known. Linear motors have applications in many systems that benefit from linear motors. One such system, which is a non-limiting example of a system that may be used with the present invention, is an active suspension system, such as an active suspension system for a vehicle suspension or for vibration or acceleration control. One non-limiting example of vibration and acceleration control is the control of undesired vibration and other accelerations of seats in a motor vehicle.

A sensing system 62 according to an embodiment of the invention senses the position of the armature 54 relative to the stator 52. In an example, this is achieved by including a first magnetic member 66 and a second magnetic member 64 that are each directly (or indirectly) mechanically coupled to the track 58 of the armature 54. The sensor structure 60 is mechanically coupled to the stator 52 or another fixed part of the assembly such that the magnetic devices 64 and 66 move in the direction of arrow 55 relative to the sensor structure 60 as the armature 54 moves in and out relative to the stator 52.

One particular embodiment of these two magnetic devices is depicted in fig. 3A. The first magnetic device 66 comprises an elongate strip defining two magnetic poles (denoted by "N" for north poles and "S" for south poles) at its sensing surface along its length. The poles meet at a location 78 that defines a magnetization state transition location. The device 66 is preferably, but not necessarily, as long as the armature travel distance. In certain embodiments, the device 66 defines a single magnetization state transition over the entirety of the armature stroke. In other embodiments, the device 66 defines more than two alternating poles along the length of its sensing surface in the direction of armature travel, thereby defining more than one magnetic state transition location. Furthermore, the device 66 preferably (but not necessarily) presents a single pole over the entire armature stroke transitioning from both stroke ends to the magnetic state, so that the sensor output can directly indicate which portion of the stroke relative to the transition armature; this is explained further below.

In this non-limiting embodiment, second magnetic device 64 is adjacent to device 66 and alongside device 66; other physical arrangements of the two magnetic devices are contemplated, as described below. The second magnetic device 64 defines a sensing surface 65, which sensing surface 65 comprises several adjacent alternating magnetic poles, such as magnetic poles 72 and 74. The alternating poles create a cyclically varying magnetic field proximate the sensing surface 65 along the stroke dimension of the armature 54. Preferably, the device 66 is at least as long as the armature stroke distance so that a circulating field is present throughout the armature stroke. But as described further below, the device 66 need not have this length. In the physical arrangement of the two magnetic devices depicted in the figures, the transition 78 may be approximately centered on the sensing surface of device 66 and may be approximately centered on the sensing surface of device 64, although this arrangement is not required and is not a limitation of the present invention.

The present invention contemplates other ways of creating and/or sensing a cyclical variation in the stroke length along the relatively movable portion of the assembly, whereby the cycle, together with the position within the cycle, indicates an absolute position. For example, the optical sensor may sense a monotonically changing characteristic located on a portion that moves across the sensor. A two-dimensional charge coupled device may sense active or passive (e.g., reflective) light sources that are laid out, presenting the necessary variability, for example, by arranging the light sources along a curve (e.g., an angled line) relative to the axis of motion.

The magnetic devices 64 and 66 may be mounted to a flange 67 coupled to the armature, for example, clamped behind the armature rail 58. In one embodiment, the flange 67 and the rail 58 may be made of a ferroelectric material. One result is that the backing flange 67 acts as a back-iron for both magnetic devices and the track 58 provides some shielding from stray magnetic fields.

A similar arrangement of magnetic devices is shown in the alternative embodiment 62a of fig. 3B. Embodiment 62a includes a third magnetic device 82 of the same shape, size and length as device 66 and located immediately beside it. The devices 82 define poles opposite to the poles of the devices 66 to which they are adjacent. This third magnetic device helps to confine the combined magnetic field from devices 66 and 82. This enables a more well defined field for the sensor 104 to sense. Furthermore, the dipole structure implemented by the combination of devices 82 and 62 reduces stray fields from the combined devices that may alter the cyclic magnetization vector present above the sensing surface 65 of device 64.

The configuration of the physical arrangement of the magnetic devices 64 and 66 (and the device 82 when the device 82 is present) may be otherwise altered. In order for the sensing system to work, the absolute position sensor needs to sense the magnetic state transition at a predefined point, and at that point the system must know its position in the current cycle of the device 64. With this information, the system can then maintain an absolute position by tracking the cycle and the position within the currently sensed cycle. Accordingly, the first magnetic device 66 may define one or more transitions along the length of travel, so long as the system maintains some means of determining which transition is sensed. If more than one transition is defined, more than one absolute position sensor may be used to resolve possible ambiguity of which transition is being sensed. Having a single transition simplifies the system because a single two-state hall sensor can thus be used as an absolute position sensor. Furthermore, the second magnetic device 64 may be located anywhere as long as it moves with the movable portion of the assembly and can be sensed by the incremental position sensor; it is not required that the two magnetic devices be placed side by side. However, positioning locating the locating devices 64 and 66 beside each other allows for a more compact arrangement of the two sensors in a single assembly, providing certain advantages. Moreover, aligning the state transition location of the device 66 with the meeting point of the two magnetic segments of the device 64 provides a visual cue that eases assembly of the system, but is by no means required.

The embodiment shown in fig. 3A and 3B illustrates that each of the two or three magnetic devices is a separate structure. However, this is not a limitation of the present invention, as the magnetic devices may be combined into a smaller (or larger) number of physical structures, as will be appreciated by those skilled in the art. For example, both of the magnetic devices shown in FIG. 3A, or all three of the magnetic devices shown in FIG. 3B, may be created in one physical structure. Alternatively, magnetic devices 66 and 82 may be created in one structure and device 64 may be separate. In the preferred embodiment, the devices 64 and 66 are separate. The bar magnet with poles created or "printed" on it that can be used in this embodiment is available from Bogen Electronic GmbH, Berlin, Germany.

Embodiments of the inventive sensing system include an absolute position sensor and an incremental position sensor. In the embodiment depicted in fig. 3B, the absolute position sensor is implemented with a hall sensor 104 positioned proximate the sensing surface 73 of the device 66. The sensor 104 is generally fixed relative to the device 66 in all degrees of freedom except for relative movement in the desired direction of travel. However, if the sensor output is substantially insensitive to some variation in the relative position of the sensor and the magnetic device in another degree of freedom, such variation may be tolerated. For example, if there is some variation in the height of the sensor 104 above the sensing surface 73 of the device 66 (e.g., due to manufacturing tolerances of the device 66 and/or the structure to which it is coupled), the sensor 104 may still detect the magnetic state transition. The sensor 104 may be a bipolar device having an output in one state when it senses one magnetic pole and a different state when it senses the opposite magnetic pole. A 1220 series sensor from Allegro Microsystems, inc. By creating a known physical position of the magnetic device 66 relative to the overall travel of the armature (or other movable portion of the assembly), the output of the sensor 104 is indicative of one of two portions of the overall travel. As the device 66 moves relative to the sensor 104 (in both directions of arrow 71), the output state of the sensor 104 will change at the magnetization state transition location 78. Since the physical relationship between the device 66 and the movable portion of the assembly being sensed (in this embodiment the armature 54) is known a priori, the output state of the sensor 104 in this example indicates which portion of its stroke the armature 54 is located. In the depicted embodiment, the length of the magnetic device 66 coincides with the overall travel of the armature, and the transition 78 is located at its center. In this case, the output of the Hall sensor 104 indicates which half of the stroke the armature is currently located.

There are other possible arrangements of the magnetic device 66. In order for the positioning system to determine the direction to move for sensing a state transition at startup, the device 66 must cover at least the portion of the armature stroke from the transition position to one armature stroke end; in this case, if a pole of the device 66 is sensed, the system will know that the armature is in that portion of the stroke and will know the direction to move to sense the transition. Alternatively, if the sensor 104 is a unipolar hall sensor with no output when not located near the poles, the absence of an output is interpreted as the sensor not being located above the device 66, in which case the system will know that the armature is in the portion of its stroke not covered by the device 66, and will know the direction to move to sense the transition. In the limit, it is possible for the device 66 to define only a single pole at its sensing surface without a transition, and as long as the pole is at a defined position above the armature travel (the "home" position), the positioning system will be able to operate by moving (possibly randomly within the normal range of motion) at start-up until the pole is sensed.

Incremental position sensor 102 is positioned proximate to sensing surface 65 of device 64. The sensor 102 is generally fixed relative to the device 64 in all degrees of freedom except for relative movement in the desired direction of travel. However, if the sensor output is substantially insensitive to some variation in the relative position of the sensor and the magnetic device in another degree of freedom, such variation may be tolerated. For example, if there is some variation in the height of the sensor 102 above the sensing surface 65 of the device 64 (e.g., due to manufacturing tolerances of the device 64 and/or the structure to which it is coupled), the sensor 102 may still detect the magnetic field angle. The output of sensor 102 is repeated twice for each cycle of magnetic device 64 as device 64 moves relative to sensor 102 in the direction of arrow 71.

In one non-limiting embodiment, the incremental position sensor 102 may be a magnetoresistive device that senses the angle of the magnetic field of the second magnetic device and has a 180 ° output that varies monotonically (increases or decreases) with respect to the magnetic field angle (except when the device is reset between its maximum and minimum values, causing its output to be momentarily discontinuous, as explained further below), and repeats twice on each 360 ° cycle. Alternatively, the sensor 102 may be a hall effect field direction sensor with a 360 ° output that varies continuously over each cycle of the magnetic field. Both types of sensors are known in the art. In a preferred embodiment, a magnetoresistive KMA-200 sensor available from NXP Semiconductors, Eindhoven, The Netherlands is used.

The operation of the hall sensor and the magnetoresistive sensor in the preferred embodiment is further explained with reference to fig. 4A, 4B, 4C, 5A, 5B and 6. Fig. 4A schematically depicts a portion of a second magnetic device 64 on which the sensing surface 65 defines alternating poles that create a cyclically varying magnetic field 110 near the surface 65. The sensor 102 is positioned approximately at the measurement line 109 such that it senses the angle of the field 110. Fig. 4B depicts the x and y flux density components along measurement line 109, where direction x is the direction of motion of magnetic device 64 and direction y is the direction toward and away from surface 65. As shown in fig. 4B, the magnetic field angle varies sinusoidally. One cycle of the magnetic field of device 64 is created by each pair of adjacent north-south magnetic poles. One arbitrarily defined cycle depicted in fig. 4A-4C begins at the "origin" location 111 where the magnetic segment or portion 117 meets segment 119 (the S-N transition at sensing surface 65) and extends to the location 113 where segment 121 meets segment 123 (the next S-N transition) and includes the field adjacent the sensing surfaces of both segments 119 and 121. This same cycle is shown in fig. 4B and 4C. The output of the sensor 102 varies continuously with angle except for discontinuities where the output is reset by jumping or flipping between maximum and minimum values.

Since magnetoresistive sensor 102 has a 180 ° output, rather than a 360 ° output, the output of the sensor (shown in fig. 4C) repeats twice (two cycles) for each cycle of the cyclically varying magnetic field shown in fig. 4B. The output of the sensor 102 monotonically increases from zero to 180 ° over a stroke distance (width in the stroke direction) equal to the width of the magnetic pole or segment. The output repeats regularly over the entire distance of travel, assuming that the segments have the same width. The output of the sensor 102 is arbitrarily set so that it is approximately at its median (90 °) value at each meeting point between adjacent segments, and moves between a maximum and minimum value at the approximate center of each segment. However, this arrangement is not a limitation of the present invention, as the sensor output will change continuously as the magnetic field angle changes, regardless of the location of the origin position, and regardless of the change in field angle that causes the sensor output to move substantially instantaneously between its maximum and minimum values.

Fig. 5A and 5B illustrate the two-state output of the hall sensor 104 (state "0" or state "1") and the output of the magnetoresistive sensor 102 (angle, from 0 ° to 180 °) according to the x-position relative to the magnetic devices 66 and 64, respectively, for a preferred embodiment. The output state change of the hall sensor occurs once over the stroke of the relatively movable member or portion (e.g., over the stroke distance of the armature) at what is referred to as the "home" position 78 of the sensor system (the position labeled as position "0" in fig. 5A and 5B). Preferably, the two magnetic devices and the sensors associated with these magnetic devices are physically arranged so that the incremental position sensor is sensing a known cycle when the absolute position sensor is sensing a state transition. This allows the sensor system to determine the absolute position at the sensing state transition and then maintain absolute position sensing as the portion is moved from the origin position. A condition that should be avoided to avoid ambiguity in position determination is that the incremental position sensor is in its transition (bouncing or flipping between its low and high angular outputs) when the absolute position sensor is sensing a state transition.

As the movable portion of the assembly then moves from its home position, the output of the incremental position sensor repeats cyclically over a distance equal to the width of each pole or "segment". If the system maintains knowledge of the cycle or segment being sensed, the output of the incremental position sensor thus indicates the absolute position of the movable portion relative to the fixed portion (position within the cycle and the cycle).

In order for the system to track the cycling of the incremental position sensors as movement from the home position occurs, one design constraint is that the maximum distance traveled by the sample of each incremental position sensor 102 must remain less than the distance from the home position to the closest position (in a non-limiting preferred embodiment, the center of each pole) at which the output jumps or flips between its high and low values when traveling at maximum speed. If this constraint is not satisfied, there is a possibility of moving from the origin position past the transitions on either side of the "origin" position without sensing the magnetic field angle (and thus the position). This will cause the control system to lose its track of the count of magnetic segments of the device 64.

There is a magnetic pole width (w) (meters) of the incremental magnetic stripe that will allow successful decoding of the displacement, the sampling rate (f) of the control system_s) (samples per second) and maximum velocity (v) of the sensor strip relative to the incremental position sensor_max) (meters per second). The incremental position sensor has a full range output of 180. The decoder identifies jitter or flip by looking for a change in the angular measurement from sample to sample that is greater than the normal maximum angular change. In one example, to ensure that decoding is possible, the normal change in angle measurement at maximum speed needs to be less than |90 ° |. Thereby to obtain

180°/(W/v_max x fs)＜90°

Fig. 6 is a graph of incremental position sensor output data taken using the embodiment shown in fig. 2 and 3B as it moves relative to magnetic segments 117, 119, and 121. In the case of a linear motor operating so that the incremental position sensor output occurs at intervals of about 0.5mm (ten samples of 5mm width of the magnetic segments or poles of each magnetic device 64), and in the case of a 180 ° output from a magnetoresistive sensor, there is a maximum normal operating change of angle of no more than 18 degrees per data point. The run-time decoding of segment count (N) is as follows (N ═ 0 at the origin): when traversing in the + x direction (to the right in fig. 6), the segment count is increased (N +1) if the difference in angular output between the current measurement and the previous measurement is less than-90 ° (so that a jump or flip from maximum to minimum has occurred). When passing in the-x direction, the segment count is reduced (N-1) if the difference in angular output between the current measurement and the previous measurement is greater than +90 ° (so that a jump or flip from maximum to minimum has occurred).

FIG. 7A is a flow chart 200 illustrating startup using one embodiment of the present invention. After start (step 202), the output of the incremental position sensor (referred to as "MR" for magnetoresistive sensors) is decoded (step 204) as a means of determining position relative to any particular sensing cycle. The output state of the absolute position sensor (referred to as the hall state) is determined (step 206). One state (arbitrarily referred to as "0") indicates a portion of the relative movement of the relatively movable portions of the assembly. If the state is sensed, the movable portion is moved toward the state transition or home position (referred to as the "positive" direction) (step 208). If another state is sensed (state "1"), the movable portion is in another different portion of the overall relative movement, so the movement is forced in another direction (referred to as "negative") (step 210). The move continues until the state changes (referred to as a "successful homing") (step 212). If the displacement since the start exceeds the maximum allowable displacement (or "flag") from one end of the stroke to the position of the magnetic state or hall transition, an error is indicated (step 214). Otherwise, the decoding state of the incremental position sensor is reset at the home position (step 216). Runtime decoding of the incremental sensor then begins (step 218), and operation moves to the flowchart 230 of FIG. 7B.

An incremental segment counter is initialized (step 232). With reference to the above description, this means that the counter is set to the origin magnetic segment or pole. The incremental position sensor output is used to determine its change (step 234). If the sensor output has been repeated (step 236), the counter is changed (step 240). The actual displacement is then calculated (step 238). The segment is known (counter N) and this together with the incremental position sensor output is sufficient to allow the controller to determine the absolute position. Alternatively, if only a coarse position needs to be known (e.g., within the width of a segment of the magnetic device 64), the absolute position may be based on the cycle being sensed rather than the relative output of the incremental position sensors.

If the counter is consistent with the state of the absolute position sensor (step 242), normal operation continues. If the inconsistency indicates that the system has lost some tracking of the segment, an error is indicated (step 244). The error may also be based on a discrepancy between the number of segments that have been counted (moved over) compared to the number of whole segments. For example, if there are 10 segments in each half of the movement (on each side of the home position), while the controller has tracked motion over 11 segments in half of the armature stroke, an error is indicated. The tracking segment is equivalent to a tracking magnetic field cycle, since there are two poles or segments per cycle of the magnetic field near the sensing surface of the device 64.

An environment in which the present invention may be used is shown in FIG. 8. This is a non-limiting example of a positioning system that may be used with the present invention. The system 300 includes a vehicle seat 302 that moves up and down longitudinally (in the direction of arrow 312) to counteract vibration and other acceleration of the seat 302. The active longitudinal seat suspension system 304 affects the movement of the seat 302 relative to the fixed base 306. The active suspension system 304 includes one or more actuators as an integral part thereof. The actuator is capable of generating a force whose magnitude and direction can be controlled independently of the position and movement of the suspension. In some embodiments, one actuator is an electromagnetic actuator such as a linear or rotary, single or multi-phase electromagnetic motor. In this example, the actuator 308 is a multi-phase electromagnetic linear motor, while the actuator 310 is a single-phase force bias eliminator, which may be implemented using an air cylinder.

FIG. 9 illustrates a control and positioning system 320 that may be used with the active suspension seat of FIG. 8. The control and positioning system 320 includes one actuator 326 designed and operated to eliminate force bias on a movable portion or device 322 (e.g., the seat 302), and a second actuator 324 designed and operated to minimize acceleration on the device 322. The force bias eliminator 326 can be a single phase actuator designed to eliminate force bias so that the second actuator 324 that counteracts acceleration does not need to maintain a dc force. One example is a cylinder that is inflated or deflated to change the position of the seat. Absolute position sensors and incremental position sensors (neither shown in the figures) sense the position of the device 322 and provide their outputs to the decoder 330, the decoder 330 outputting the absolute position of the device 322. The control algorithm 332 establishes the appropriate control signals and provides them to the actuator 324 (linear motor) via power electronics 334 and to the actuator 326 via a pressurized air source 336. The brake 324 is controlled to counteract the seat acceleration.

The system 320 is initialized as follows. An absolute position sensor is used to determine which half of the stroke the armature (and thus the seat) is located. The controller then causes the cylinder to move the seat toward the home position by inflating or deflating the cylinder as needed. When the origin position is sensed, the system can determine the absolute position of the seat.

Other embodiments are within the scope of the following claims.

Claims (10)

1. An apparatus, comprising:

a linear motor including a stator and an armature movable relative to the stator over a stroke distance;

a first magnetic device coupled to the armature, the first magnetic device defining a sensing surface comprising a plurality of magnetic poles providing magnetization state transition locations therebetween;

a magnetic pole sensor coupled to the stator adjacent the first magnetic device such that as the armature moves relative to the stator over the travel distance, the first magnetic device moves past the magnetic pole sensor, the magnetic pole sensor sensing adjacent magnetic poles of the first magnetic device, the magnetic pole sensor having a two-state output, wherein one state of the magnetic pole sensor output indicates a first portion of the relative movement of the armature relative to the stator and another state indicates a second, different portion of the relative movement;

a second magnetic device coupled to the armature, the second magnetic device defining a sensing surface comprising a plurality of adjacent alternating opposite magnetic poles that create a cyclically-varying magnetic field near its sensing surface; and

a magnetic field angle sensor coupled to the stator adjacent the second magnetic device such that as the armature moves relative to the stator, the cyclically-varying magnetic field of the second magnetic device moves past the magnetic field angle sensor, the magnetic field angle sensor sensing an angle of the magnetic field of the second magnetic device and having an output that varies continuously in relation to the magnetic field angle over at least a portion of one cycle of the cyclically-varying magnetic field.

2. The apparatus of claim 1, wherein the magnetic pole sensor comprises a hall sensor.

3. The apparatus of claim 2, wherein the magnetic field angle sensor comprises a magnetoresistive sensor.

4. The apparatus of claim 3, wherein the magnetic field angle sensor comprises a bipolar Hall sensor and the magnetic field angle sensor has a full range output of 180 ° such that its output repeats twice for each magnetic field cycle of the second magnetic device.

5. The apparatus of claim 1, wherein the first magnetic device is at least half as long as a stroke distance of the armature, and the second magnetic device is at least as long as the stroke distance of the armature.

6. The apparatus of claim 1, wherein adjacent poles of the second magnetic device meet at a magnetization state transition location, and wherein the first and second magnetic devices are coupled to the armature such that a known and defined spatial relationship exists between the magnetization state transition location of the first magnetic device and at least one magnetization state transition location of the second magnetic device.

7. The apparatus of claim 6, wherein the transition location of the first magnetic device is approximately centered with respect to a length of the sensing surface of the second magnetic device.

8. The apparatus of claim 6, the magnetic field angle sensor output resetting in at least one position on each magnetic field cycle, and wherein the first and second magnetic devices are arranged such that when the magnetic pole sensor is adjacent to a transition position of the first magnetic device, the magnetic field angle sensor is not adjacent to a position where it resets.

9. The apparatus of claim 1, further comprising a third magnetic device coupled to the armature adjacent to the first magnetic device, the third magnetic device defining a sensing surface that defines a single magnetization state transition location over an armature travel distance, wherein the sensing surfaces of the first and third magnetic devices each include at least two magnetic poles, and wherein adjacent magnetic poles of the first and third magnetic devices have opposite polarities.

10. The apparatus of claim 1, wherein:

adjacent poles of the second magnetic device meet at a magnetization state transition location, and wherein the first and second magnetic devices are coupled to an armature such that there is a known and defined spatial relationship between the magnetization state transition location of the first magnetic device and at least one magnetization state transition location of the second magnetic device, and wherein the magnetic field angle sensor output resets at one or two locations on each magnetic field cycle, and wherein the first and second magnetic devices are arranged such that when the pole sensor is adjacent to the transition location of the first magnetic device, the magnetic field angle sensor is not adjacent to the location at which it resets.