HK1066269B - Adjustable probe - Google Patents

Description

Adjustable probe

Technical Field

The present invention relates to a touch trigger probe that is spatially oriented in multiple directions. The probe is designed in particular, but not exclusively, for use in manually operated or automatic measuring machines or in machine tools, such as milling machines, for the measurement of three-dimensional dimensions of workpieces that have been or are being machined.

Background

Touch trigger probes are widely used measurement instruments in the processing line of mechanical workpieces (but not limited thereto) to accurately check the dimensions or surfaces of the mechanical workpieces. Touch trigger probes are also used for three-dimensional measurement of complex shaped workpieces in order to replicate or profile them.

Generally, touch trigger probes comprise a fixed part designed to be fastened to a measuring machine or machine tool and a moving contact comprising a ball on the end of its elongated rod and designed to come into contact with the workpiece to be measured.

In most applications, touch trigger probes are fastened to the moving arm of the machine, the spatial position of which is measured accurately with the aid of a manually operated or automatic measuring system, for example a position encoder placed on the machine shaft. The motion arm moves spatially so that the measurement probe of the probe is brought into contact with the workpiece or surface to be measured. During contact, a biasing force then acts on the contact to move it away from the initial rest position. The sensors react to small movements of the feelers, generating electrical signals that are sent in the form of optical signals to the user or to the machine control software, thus determining the coordinates of the point of contact in a given reference frame, according to the data of the measuring system. For this purpose, electromechanical or optical sensors or motion sensors according to different theories are used in the art, which sensors for example comprise a constrained measuring instrument.

In the case of three-dimensional touch trigger probes, the connection between the feeler and the fixed part of the probe is generally achieved by the theory of a Boys connection, for example by three cylindrical pins resting on six spheres defining the contact point between the fixture and the feeler. Two-dimensional and one-dimensional probes are therefore known.

When a probe is used to measure a workpiece having a complex shape with a hollow and a protrusion, it would be difficult, if not impossible, to bring the stylus into contact with the entire surface of the workpiece without the fixed portion of the probe or stylus stem interfering with the components of the workpiece to be measured. To compensate for this drawback, known probes orient the contact tips in a plurality of spatial directions. Typically, two separate axes of rotation are required to cover all possible orientations. A probe of this type is described in European patent application EP-0392660-A2.

The pivot axis is preferably indexable to provide a sufficient number of predetermined and precisely reproducible rest positions. This indexing avoids the need to calibrate the measuring machine each time the orientation of the stylus is changed.

During the measurement, the axis of orientation of the prior art probe is locked in a set indexed position. When a different orientation of the probe is required, the user must unlock the shaft manually by acting on a wheel or lever provided for this purpose, orient the shaft as required, and lock the shaft by repositioning the wheel or lever again in its initial locked position. These operations may create positioning errors, such as inadvertent movement of the first axis during positioning of the second axis.

Another drawback of the described probe is that locking and unlocking require an external torque acting on the locking wheel and transmitted to the moving arm of the measuring machine through the probe and its support. This net torque causes mechanical forces on the probe support and may cause the entire probe to move. To avoid this drawback, the user must hold the probe still while operating the locking wheel, which makes it difficult or impossible to do so with one hand.

Disclosure of Invention

It is therefore an object of the present invention to provide a touch trigger probe which can be orientated in a plurality of indexing directions and which is simpler to operate than prior art probes.

It is another object of the present invention to provide a touch trigger probe that does not have the limitations of the prior art.

According to the present invention, these objects are achieved by the subject matter of the main claims and notably by an adjustable contact-triggered probe for orienting a measuring feeler with respect to a measuring device, the probe comprising:

a moving element rotatable about an axis; elastic means for retaining said moving element in a locking position so as to prevent movement of said moving element; an actuator opposed to the elastic means and for rotating the first moving element about the axis by moving in the direction of the axis and disengaging the moving element; a force transfer mechanism designed to provide an increased reduction ratio to reduce the amount of force holding the moving element in the disengaged position.

Drawings

The invention will be better understood from a reading of the description given by way of example and illustrated by the accompanying drawings, in which:

FIG. 1a shows a first embodiment of a touch trigger probe according to the present invention;

FIG. 1b shows a fixed part of the touch trigger probe of the present invention shown in FIG. 1 a;

FIGS. 1c and 1d illustrate an indexing mechanism of the touch trigger probe of the present invention shown in FIG. 1 a;

FIG. 1e shows a reduction mechanism for disengaging the first axis of the probe of FIG. 1 a;

FIGS. 2a, 2b and 2c show sectional elevation views of the indexing and reduction mechanism of the second axis of the probe of FIG. 1 a;

fig. 3 and 4, 5a, 5b and 5c show a second embodiment of the invention.

Detailed Description

The first embodiment of the invention shown in fig. 1a to 1e is a touch trigger probe 20 comprising a fixed part 250, shown in detail in fig. 1b, designed to be fastened to the moving arm of a measuring machine by means of a threaded rod 251 or any other known fastening means.

The fastening part 250 carries balls 256 on its underside 24, which are distributed uniformly in the circumferential direction and project partially downward. The sphere 256 defines 24 index positions spaced at 15 degree intervals about the first axis of rotation of the probe, as explained further below. It will be apparent that a different number of spheres may be used depending on the number of indexing positions required.

The moving element 20 shown in fig. 1c and 1d carries three cylindrical pins 217 on its upper side. The flat spring 215 presses the moving element 210 against the fixed element 250. In this case, each pin 217 rests on two spheres 256, thus creating six points of contact that determine the relative position of the elements 250 and 210 in a precise and repeatable manner.

Considering the rotational symmetry of the fixed element, the mobile element 210 has 24 indexed positions around a first axis of rotation 211 corresponding to the geometric axis of the probe and at a distance of 15 degrees from each other. The same result has been obtained by equivalent structures, for example by placing a sphere on the moving element and a pin on the fixed element, or by replacing the spherical or cylindrical surface of the pin or sphere by an inclined surface, or by using six cylindrical pins, which have only one point of contact with one of the spheres. The flat spring 215 can also be replaced by equivalent elastic means, for example by a cylindrical spring or a leaf spring or by an element made of elastic synthetic material.

The decoupling mechanism 300 shown in fig. 1d and 1e allows the moving element 210 to rotate about the axis 211. The transfer device 300 comprises a gear 301 driven by four racks 305 and an inclined helical surface 302.

When two opposite buttons 310 are pressed, rack 305 drives gear 301 and inclined plane 302 to rotate so as to slide on its bearings (not shown) and move fixing element 250 axially away from moving element 210. In its separated position, the ball 256 extends beyond the pin 217 without contacting it and can rotate about the axis 211.

The resting force of the pin 217 on the ball 256 must be large enough to prevent any accidental movement of the moving element 210 during the measurement. In this particular embodiment, the spring 215 is configured to have an overall resting force of about 30N, i.e., about 10N for each of the six contact points, due to the pressure applied at 60 degrees relative to the axis.

It would be difficult to directly apply a force of 30N to the button 310. To this end, the inclined surface 302 is chosen so as to give a sufficient reduction ratio between the radial force acting on the button 310 and the axial force opposing the elasticity of the spring 215. The reduction ratio of 1: 2 means that the operating force acting on the button 310 is about 15N, i.e., about 1.5Kgf, and the user does not have difficulty in acting. With this reduced scale, the travel of the button 310 is maintained within a few millimeters.

The inclined spiral surface 302 is preferably not straight but protrudes slightly upward so that the slope of its top is less than the slope of its bottom. The reduction ratio between the axial force acting on the moving element 210 and the radial operating force acting on the push button 310 is therefore not constant, but increases with the distance between the elements 250 and 210.

The reduced-scale variation is advantageous since the force required to keep the push button pushed at its end of travel is small, which makes it easier to perform fine-adjustment operations of the contacts 30.

The numerical values given above must be interpreted as examples particularly suitable for the embodiments of the invention. Different values may be selected as the case may be, for example, as a function of the mass and size of the probe.

To ensure that the moving element 210 is disengaged around the rotation axis 211, it is necessary to act on two opposite buttons 310. In this way, the external forces acting on the probe are substantially opposed and perpendicular to the axis of rotation 211, the resulting forces and torques are substantially zero, and any unintentional movement of the probe is prevented.

While the push buttons 310 are pressed radially, the user can rotate the movement element 210 about the axis 211 by acting tangentially on the same push buttons. This operation is very intuitive and can be conveniently performed by two fingers of the hand. In this case, the distance between the ball 256 and the pin 217 is sufficient to avoid any contact or friction of the indexing surfaces, thus maintaining the positioning accuracy of the indexing positions. Thus, there is no need to release the operation of the button 310 from being unlocked to the probe rotation and then locking the probe again.

The reduction ratio and the coefficient of friction of the materials used are chosen such that the transmission device 300 is reversible, so that the mobile element 210 automatically returns to the indexed position once the pressure on the button 310 is released, thus avoiding the accidental use in the free position.

The first mobile element 210 is connected to a second mobile element 220 able to rotate about a rotation axis 212 perpendicular to the first rotation axis 211, to which a mobile contact 30 of known type is fastened, as shown in figure 2 a.

The second moving element 220 is pressed against the first moving element 210 in the axial direction defined by the rotation axis 212 by a compression spring 225. The crown of the sphere 226 is arranged on the vertical side of the mobile element 220 and interacts with three cylindrical pins (not shown in the figures) placed on the adjacent side of the first mobile element 210 in order to define a predetermined number of indexing positions that can be accurately and repeatedly achieved, in a manner similar to that described for the rotation of the first mobile element 210.

In a possible variant embodiment, six cylindrical pins are used, each having a single contact point.

The disengagement and rotation system 400 of the second kinematic element 220 is shown in fig. 2 b. Disengagement is performed by pressing both buttons 411 and 410. The axial force acting on the button 410, which can slide axially around the part 470, is transmitted through the two levers 430 and 450 and the horizontal arm 440, this force being amplified by the pin 461 and the lever 460 and acting on the spring 225 so as to compress it, this force counteracting the contact force between 220 and 210. In this embodiment, the dimensions of the arms of the bars 430, 450 will be chosen to obtain a reduction ratio of 1: 2 for the first kinematic element 210. A second spring 475, placed between the button 410 and the member 470, pushes the second kinematic element 220 axially to the right in fig. 2a and causes it to rotate.

When the button 410 is pressed, the second movement element 220 moves towards the right in fig. 2a, so that the pin and the index sphere 226 are no longer in contact and the second movement element 220 can rotate about the axis 212. This rotation is felt by the user through the button 410, which is angularly engaged with the member 470 by means of a pin, not shown in the figures.

The button 411 opposite the button 410 has the dual function of giving the finger rest surface to exert a force opposite to the force acting on the button 410 and to facilitate turning of the element 220 by two fingers. The button 411 is in fact angularly coupled to the element 220 and is driven in rotation with the latter. The use of two forces, generally opposed, prevents the transmission of forces to the probe support and prevents movement of the entire probe.

The action of the button 410 on the second motion element 220 by the lever 460 is substantially aligned and in the opposite direction to the force of the spring action, which ensures a linear motion without any obstruction.

The electrical signals generated by the feelers 30 are sent to the user (fig. 1a) in the form of optical signals generated by the light-emitting diodes 50, or to the control software of the machine, which determines the coordinates of the contact point in a given coordinate system, according to the data of the measuring system.

The lower portion of the probe 20 has one or more protective elements 218 that extend out of the probe body and function to protect the indexing mechanism from impact with the work piece being measured or the support table. The protective element 218 may be an enlarged portion formed by machining directly on the metal shell 217 or an additional element made of a suitable material capable of absorbing impact, such as rubber or elastomer.

For a total angle of 90 degrees, the second kinematic element 220 may have 7 index positions spaced 15 degrees apart from each other in this embodiment. When the first rotating element 210 can be rotated 360 degrees, this angle causes the contacts 30 to be oriented in a number of directions evenly distributed in half the space. The device of the present invention can be implemented with a general number of indexing positions and with any distance between indexing positions.

Fig. 4, 5a and 5b show a second embodiment of the invention, in which the uncoupling means 300 of the first axis 211 are realized by four pairs of identical and symmetrical connecting rods 320.

In this embodiment, each pair of connecting rods 320 is hinged with respect to the mid-point 232, and when the two ends of the two connecting rods of a pair rest with one end on the fixed element 250 and the other end on the first kinematic member 210, the two external forces acting on the push button 310 are transmitted to said mid-point 323.

In this configuration, the reduction ratio between the axial force acting on the moving element 210 and the radial operating force acting on the button 310 is proportional to the tangent of half the aperture angle between the connecting rods 320. This results in a reduction ratio that increases with the distance between the elements 250 and 210 and the angle between the connecting rods 320. The reduced-scale variation is advantageous since the force required to keep the push-button pressed at its end of travel is minimal, which makes it easier to perform fine-tuning operations of the contacts 30.

This advantageous feature may also be achieved in the first embodiment by using a non-planar surface instead of the inclined surface 302.

When the button 310 is fully pressed, the distance between the ball 226 and the pin juxtaposed to it is maintained, and the ball and the pin are in any case not in contact with each other or with other elements of the probe mechanism. In this case, the wear of the indexing surface is reduced to the minimum required, and the indexing accuracy is maintained over time.

When the user presses the two opposite buttons 310, the force acting on the first kinematic element 210 through the connecting rod 320 is substantially axial with respect to the rotation axis 211, i.e. substantially aligned and opposite to the force acting by the spring 215, thus ensuring a linear movement without obstruction. On the other hand, if the operator presses asymmetrically on only one of the buttons 310, the resulting horizontal component of force creates a large friction between the rod 253 and the sleeve 219, thereby preventing the first movement member 210 from disengaging. This advantageous feature makes it possible to prevent untimely and unintentional operation.

The button 310 is surrounded by a protective ring membrane 330 made of rubber or elastomer, which functions to protect the inner mechanism from dirt and dust, as well as to prevent heat from the user's hand from being transferred to the inner indexing mechanism, which has a negative effect on the indexing accuracy. For the same purpose, the buttons 410 and 411 for turning and disengaging the second axis 212 are also preferably made of a synthetic material having good insulating properties.

The window 30 is provided on the support member 250 such that the rotation angle with respect to the first axis 211 can be read through a scale engraved or printed on the first moving member 210, as shown in fig. 5a and 5 b.

The angle of rotation with respect to the second axis 212 can be read in two windows 40 provided in the outer crown of the push-button 411, as shown in fig. 5a and 5 b. Two windows are in this case required to optimize the visibility of all possible orientations of the probe.

In this latter embodiment of the invention, the probe of the invention is arranged for reading the angle of rotation relative to the first and/or second axis without including a force transmission mechanism designed to provide an increased reduction ratio in order to reduce the amount of force required to hold the moving element in the disengaged position.

The trigger feeler 30 responds to the slightest contact with the surface of the workpiece to be measured by generating an electrical pulse. The pulses are transmitted by an electronic processing circuit (not shown) to a connector 70 for connection with the control means of the measuring machine and the light indicator 50. The indicator comprises a light emitting diode in this embodiment, but may alternatively comprise other known light emitters, such as a sheet or wire shaped electroluminescent element. The top of the led is placed with an optical diffuser so that the diffuse light can be seen over a wide range of viewing angles.

In an alternative embodiment of the invention, the indicator 50 is replaced by a plurality of indicators placed at different positions on the probe so that at least one indicator is visible from any possible viewing angle.

In another embodiment of the apparatus of the present invention, the indicator 50 comprises one or more light pipes for releasing light generated by one or more light sources at different locations on the probe surface so that the indication of light is visible from any possible viewing angle.

In the latter embodiment of the invention, the probe of the invention is provided with one of said light indicators 50, without comprising a force transmission mechanism designed to provide an increased reduction ratio in order to reduce the amount of force required to keep said mobile element in the disengaged position.

The invention can also be implemented without the use of an indexing mechanism, but with a simple friction mechanism, allowing the shaft to be locked in a number of orientations.

The invention also includes embodiments in which the rotation and disengagement of the shaft is performed by an automatic actuator, for example by means of an electric motor and/or a solenoid valve.

In another embodiment of the invention, the rotation of the probe shaft is ensured by a servo motor comprising an encoder for measuring the azimuth angle of the stylus. In this case, the indexing mechanism may be retained or omitted if the accuracy of the servo motor is sufficient for the application to be performed.

Claims (11)

1. An adjustable touch trigger probe (20) for orienting a measurement stylus (30) relative to a measurement device, the probe comprising:

a first motion element (210) rotatable about a first axis (211);

-first elastic means (215) for retaining said first kinematic element (210) in a locking position, preventing the first kinematic element (210) from moving;

-a first actuator (300) opposite to said first elastic means (215) and intended to disengage said moving element (210) by moving in the direction of said first axis (211), so that said first moving element rotates about said first axis (211);

a force transfer mechanism designed to provide an increased reduction in the magnitude of the force required to hold the moving element in the disengaged position.

2. The probe according to claim 1, wherein said first actuator (300) is designed to stop its action when said force is interrupted.

3. The probe according to claim 1, characterized in that said first actuator (300) disengages said moving element by the action of two external forces acting substantially symmetrically and oppositely on said actuator.

4. The probe of claim 3, wherein the force transfer mechanism comprises at least two pairs of symmetrical connecting rods, each pair of connecting rods being articulated relative to a midpoint to which the external force is transferred.

5. A probe according to claim 3 wherein said force transfer mechanism comprises at least one helical surface forming an inclined plane or an inclined curved surface and driven by rotation of a rack upon which at least two of said external forces act.

6. The probe of claim 1, further comprising one or more windows for indicating the angular position of the first moving element.

7. The probe of claim 6, further comprising at least two windows for indicating the position of the first moving element.

8. The probe of claim 1, further comprising a large-scale light indicator that allows control of the operation of the probe at all measurement positions.

9. The probe of claim 8, further comprising a plurality of light emitting elements positioned at different locations such that operation of the probe can be controlled at all measurement locations.

10. The probe according to any of claims 1 to 9, further comprising an indexing element (256, 217, 226) for defining a plurality of predetermined and repeatable realized angular positions of the first moving element (210).

11. The probe of any one of claims 1 to 9, comprising:

a second kinematic element (220) connected to the first kinematic element (210) by a second axis (212) perpendicular to the first axis (211) so as to rotate the second kinematic element (220) with respect to the first kinematic element (210);

second elastic means (225) actuated independently of said elastic means (215) and intended to keep said second kinematic element (220) in a locked position and to prevent the rotation of said second kinematic element (220);

a second actuator (400) independent of said actuator (300) and adapted to disengage said second kinematic element (220) and to rotate said second kinematic element (220) about said second axis (212);

a reduction mechanism for reducing the amount of force required to disengage the second motion element (220);

the measuring feeler (30) is connected to the second moving element (220).