Multi-component force-torque sensing device with reduced cross-talk for twist-compression testing machine

Abstract

The invention provides a method and a multi-component force-torque sensing device with reduced cross-talk between the sensitive elements. The device contains a mounting base, which supports force sensitive unit and torque sensitive unit. These sensitive units are interconnected by a sensor cross-talk reducing member via respective adapters in such a way that the force is translated to the force sensitive unit without affecting or disturbing the torque sensitive unit, and the torque is translated to the torque sensitive unit without affecting or disturbing the force sensitive unit, thus reducing the cross-talk between the force and the torque measurements.

Claims

1. A multi-component sensing device for measuring a force acting in a first direction and a torque having an axis of rotation and acting in a second direction which is different from the first direction and is not parallel thereto, with reduced cross-talk between the measured force and the measured torque, said multi-component sensing device comprising: a mounting base having a first mounting surface and a second mounting surface; a force sensitive unit for sensing the force, said force sensitive unit connected to the mounting base at the first mounting surface; a torque sensitive unit for sensing the torque, said torque sensitive unit connected to the mounting base at the second mounting surface; a test specimen/probe holder for supporting a test specimen or a test probe, said test specimen/probe holder having an axis that coincides with the first direction; a sensor cross-talk reducing member comprising a force translating twisting adapter and a torque translating adapter, wherein the force translating twisting adapter is rigid in the first direction and is moveable in the second direction and connects the test specimen/probe holder with the force sensitive unit, while the torque translating adapter is moveable in the first direction and having a high torsional stiffness in the second direction and connects the test specimen/probe holder with the torque sensitive unit.

2. The multi-component sensing device according to claim 1, wherein the force and the torque are acting in mutually perpendicular directions and the axis of rotation of the torque coincides with the first direction.

3. The multi-component sensing device according to claim 2, wherein the torque sensitive unit comprises at least one torque-sensitive element selected from a group consisting of a strain gauge sensor, a piezo sensor, a capacitive sensor, an inductive sensor, an optical sensor, and an opto-electronic sensor; said torque-sensitive element producing an output signal proportional to applied torque; said torque-sensitive unit further comprises a signal processing module having at least one input and one output; said at least one torque-sensitive element connected to said at least one input of the signal processing module; said signal processing module produces an output signal proportional to the input signal.

4. The multi-component sensing device according to claim 2, wherein said force-sensitive unit comprises at least two force-sensitive elements, each selected from a group consisting of a strain gauge sensor, a piezo sensor, a capacitive sensor, an inductive sensor, an optical sensor, and an opto-electronic sensor; said at least two force-sensitive elements each producing an output signal proportional to applied force; said force-sensitive unit further comprises a signal processing module having at least two inputs and one output; said at least two force-sensitive elements connected to said at least two inputs of the signal processing module; said signal processing module produces an output signal proportional to the sum of input signals.

5. The multi-component sensing device according to claim 2, wherein said force-sensitive unit comprises at least one toroidal-shaped force-sensitive element selected from a group consisting of a strain gauge sensor, a piezo sensor, a capacitive sensor, an inductive sensor, an optical sensor, and an opto-electronic sensor; said at least one toroidal-shaped force-sensitive element connected to said mounting base concentrically with respect to said torque sensitive unit; said at least one toroidal-shaped force-sensitive element producing an output signal proportional to applied force; said force-sensitive unit further comprises a signal processing module having at least one input and one output; said at least one toroidal-shaped force-sensitive element connected to said at least one input of the signal processing module; said signal processing module produces an output signal proportional to the input signal.

6. The multi-component sensing device according to claim 2, wherein said force translating twisting adapter comprises at least one thrust-supporting element selected from a group consisting of a ball bearing, a needle bearing, a roller bearing, a sliding bearing, a thrust bearing, an angular contact bearing, an air bearing, an x-contact bearing, a flexure suspension.

7. The multi-component sensing device according to claim 2, wherein said torque translating adapter comprises at least one movable element selected from a group consisting of a shaft coupling, a slotted-disc coupling, a spider coupling, a bellow coupling, a magnet coupling, a chain coupling, a helical coupling, a flexure coupling, a multi-disc coupling.

8. A method for reducing cross-talk in a multi-component force-torque sensing device comprising the steps of: providing a multi-component force-torque sensing device having a mounting base, a test specimen holder for supporting a test specimen, a force sensitive unit for sensing a force acting in a first direction and a torque sensitive unit for sensing a torque acting in a second direction, which is different from the first direction and is not parallel thereto; connecting the force sensitive unit and the torque sensitive unit with the test specimen holder via a cross-talk reducing member by two adapters one of which is moveable in the first direction and another is moveable in the direction of the torque, whereby during measurement of the force and the torque it becomes possible to exclude the effect of the force on the torque sensitive unit and exclude the effect of the torque on the force sensitive unit.

9. The method according to claim 8, comprising a step of applying the force and the torque in mutually perpendicular directions so that the axis of rotation of the torque coincides with the first direction.

10. The method according to claim 9, wherein the first adapter is selected from the group consisting of a slotted-disc coupling, a bellow coupling, a shaft coupling, a spider coupling, a magnet coupling, a chain coupling, a helical coupling, a flexure coupling, and a multi-disc coupling and the second adapter is selected from the group consisting of a thrust bearing, a ball bearing, a needle bearing, a roller bearing, a sliding bearing, an angular contact bearing, an air bearing, an x-contact bearing, and a flexure suspension.

11. The method according to claim 9, comprising the steps of: installing said multi-component force-torque sensing device in a friction tester having a platform, a loading unit, a rotary drive, a first specimen, and a second specimen, the force being a loading force and the torque being a friction torque; attaching the mounting base to the loading unit or to the platform of the friction tester; attaching the rotary drive to the platform or to the loading unit of the friction tester; coupling the first specimen to the test specimen holder of the multi-component force-torque sensing device; coupling the second specimen to the rotary drive; causing a relative movement between the first specimen and the second specimen while applying the loading force to the loading unit thus developing the friction torque between the first and the second specimens; causing output signals of the force sensitive unit and of the torque sensitive unit under effect of the loading force and the friction torque; and measuring the output signals in terms of the loading force and the friction torque, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a perspective view of a known device for force and torque measurement in a twist-compression testing machine or in a mechanical tester.

[0021] FIG. 2 is a perspective view of another known device for force and torque measurement based on a multi-beam elastic member.

[0022] FIG. 3 is a perspective view of a yet another known device for force and torque measurement comprising multiple flexures and a handle.

[0023] FIG. 4 is a perspective view and a cross-sectional view of a device of the invention for force and torque measurement in a twist-compression testing machine or in a mechanical tester.

[0024] FIG. 5 is a perspective exploded view of another embodiment of the multi-component force-torque sensor of the invention.

[0025] FIG. 6 is an example of an electric circuit for connecting a multi-component force-torque sensor device of the invention to the registration and measurement apparatus.

[0026] FIG. 7 is a perspective view of the multi-component force-torque sensor of the invention with three force-sensitive elements.

[0027] FIG. 8 is a perspective exploded view of yet another embodiment of the multi-component force-torque sensor of the invention with a toroidal-shaped force-sensitive element.

[0028] The invention will be explained in more details below with reference to drawings in which illustrative embodiments of the invention are shown. It is understood that the drawings are intended for illustration purposes only without limitation of the scope of protection as defined by the subject matter of the appended claims.

DESCRIPTION OF THE INVENTION

[0029] Hereinafter, it is noted that only parts necessary to understand exemplary embodiments of the present invention will be described, and description of other parts will be omitted to avoid obscuring the subject matter of the present invention. As used herein, the terms torque and moment of force can be used interchangeably to refer to the turning action of a force or combined action of several forces applied to an object and causing rotation or twisting of the object relative to a reference pivot point or an axis about which the force may be considered as causing rotation.

[0030] Referring to the figures, wherein like parts are designated with like numerals and symbols, a sensor device of the invention, which in its entity is designated by reference numeral 400, is shown schematically in FIG. 4, which represents a perspective view and a cross-sectional view of the sensor. The sensor comprises a base 401 having a first mounting surface and a second mounting surface and having mounting holes for attaching the sensor device to a testing machine, a holder 402 for supporting a test specimen or a test probe and for receiving an applied force Fz and a torque Tz, a force sensitive unit 403 attached to the base at the first mounting surface for sensing the force Fz, a torque sensitive unit 405 attached to the base at the second mounting surface for sensing the torque, and a sensor cross-talk reducing member 406 interconnecting the force sensitive unit, the torque sensitive unit, and the holder and comprising a force translating twisting adapter 409 and a torque translating adapter 410. The force translating twisting adapter is movable in the direction of the torque Tz, while being capable of translating the force Fz from the holder to the force sensitive unit without affecting or disturbing the torque sensitive unit. The torque translating adapter is movable in the direction of the force Fz, while being capable of translating the torque Tz from the holder to the torque sensitive unit without affecting or disturbing the force sensitive unit, thus reducing the cross-talk between the force and the torque measurements in the sensor device.

[0031] In the embodiment presented in FIG. 4 the force translating twisting adapter 409 comprises a plate 412 attached to the force sensitive unit 403 and a twisting element 415 mounted on the plate 412 and supporting the holder 402 in such a way that the holder can freely rotate under the action of the torque Tz, while translating the force Fz from the holder to the plate and to the force sensitive unit without affecting or disturbing the torque sensitive unit. In this embodiment, the torque translating adapter 410 comprises a movable element 417, which provides for an unrestricted motion in the direction parallel to the direction of the force Fz, while having a high torsional stiffness in the direction of the torque Tz. The torque Tz received by the specimen holder is translated through the movable element to the torque sensitive unit without affecting or disturbing the force sensitive unit, thus reducing the cross-talk between the force and the torque measurements.

[0032] In the embodiment presented in FIG. 4 the movable element 417 includes a disc with slots 418 attached to the torque sensitive unit 405 and a plurality of pins 420 coupled to the test specimen holder 402 and slide-fitted into the slots in the disc 418 so that the pins can move in the slots in the direction parallel to the direction of the force Fz. The torque Tz received by the specimen holder is translated through the pins and through the slotted disc to the torque sensitive unit without affecting or disturbing the force sensitive unit, thus reducing the cross-talk between the force and the torque measurements. It is understood that the movable element 417 can be selected from a plurality of elements including shaft couplings, slotted-disc couplings, spider couplings, bellow couplings, magnet couplings, helical couplings, flexure couplings, chain couplings.

[0033] In the embodiment presented in FIG. 4 the twisting element 415 includes a thrust bearing mounted on the plate 412 and supporting the holder 402. It is understood that the twisting element 415 can be selected from a plurality of elements including thrust bearings, ball bearings, needle bearings, roller bearings, sliding bearings, angular contact bearings, air bearings, x-contact bearings, flexure suspensions.

[0034] It is further understood that the twisting element may include several bearings, as in another embodiment of the present invention shown in FIG. 5, which is a perspective exploded view of the multi-component force-torque sensor. In this embodiment, the twisting element 415 comprises two sets of thrust bearings 514 and 516 positioned at both sides of the plate 412 and preloaded by a spring 522. The torque translating adapter 410 comprises a slotted disc 418, which is attached to the specimen holder 402 having an extended shaft, and a plurality of pins 420 coupled to the torque sensitive unit 405.

[0035] The load Fz applied to the specimen holder 402 translates through the thrust bearing 514 and the plate 412 to the force sensitive unit 403 comprising two force-sensitive elements 525 and 530, thus causing corresponding changes of their output signals Fz1 and Fz2, respectively, proportional to a stress or a deformation induced in each force-sensitive element. The thrust bearing 516 and the spring 522 provide for a preload of the thrust bearing 514 while not restricting rotation of the specimen holder 402 due to the action of the measured torque Tz, thus improving vertical stability of the specimen holder assembly and repeatability and accuracy of the force and torque measurements. The torque translating adapter 410 having a low stiffness in the direction parallel to the applied load Fz doesn't restrict motion or deformation of the plate 412 and the force-sensitive elements 525 and 530 in this direction, thus not restricting translation of the applied force Fz from the specimen holder 402 through the thrust bearing 514 and the plate 412 to the force-sensitive elements 525 and 530, while preventing translation of the applied load Fz to the torque sensitive unit 405, which allows for reducing the influence of the applied load Fz on the torque measurement.

[0036] The torque Tz applied to the specimen holder 402 causes the specimen holder with the attached slotted disc 418 to rotate. This rotation translates to the pins 420 coupled to the torque sensitive unit 405, thus causing corresponding changes of an output signal of the torque sensitive unit Tz1 proportional to a stress or a deformation induced in the torque sensitive unit. The force translating twisting adapter with the twisting element 415 having low torsional stiffness doesn't restrict rotation of the specimen holder 402, while preventing translation of this rotation to the plate 412 and allowing for unrestricted translation of the torque Tz to the torque sensitive unit 405, thus reducing the influence of the torque Tz on the force-sensitive elements 525 and 530.

[0037] Each of the force-sensitive elements 525, 530 attached to the base preferably in such a way that the directions of the maximum force sensitivity of the force-sensitive elements are parallel to each other and to the direction of the applied force Fz and perpendicular to the base 401. Notably, the distance between the force-sensitive elements 525 and 530 is greater than the dimension of the torque-sensitive unit 405. In the preferred embodiment, the torque sensitive unit 405 attached to the base 401 between the force-sensitive elements 525 and 530 in such a way that the direction of the maximum torque sensitivity of the torque sensitive unit is parallel to the direction of the applied torque Tz.

[0038] It is understood that the force-sensitive elements 525, 530 and the torque sensitive unit 405 can be of any type and based on various modes of operation, including strain gauges, capacitive, inductive, piezo-electric, piezo-resonance, optical, and other sensors, used in connection with corresponding signal processing circuitry.

[0039] An example of a schematic diagram of a signal processing module 610 for the sensor device of invention is shown in FIG. 6, wherein the like parts are designated with the like numerals with the reference to FIG. 4 and FIG. 5. The output signals Fz1, Fz2 from the force sensitive elements 525, 530 of the force sensitive unit are fed to a first signal processor 620 having a signal processing function Af, which generates the output voltage Vf proportional to the sum of the signals Fz1, Fz2 from the force-sensitive elements 525, 530, respectively, which in turn is proportional to the total magnitude of the load Fz applied to the holder 402. The output signal Tz1 from the torque sensitive unit 405 is fed to a second signal processor 625 having a signal processing function At, which generates the output voltage Vt proportional to the magnitude of the torque Tz applied to the holder 402. The output voltages Vf and Vt can be measured and analyzed by any voltage measurement or data acquisition apparatus known in the art. The signal processing module 610 comprising the first signal processor 620 and the second signal processor 625 can be integrated within the sensor of invention, as shown in FIG. 6, or made as a separate unit.

[0040] It is also understood that the output signals of the signal processors 620, 625 can be generated in a form of an output voltage, an output current, a charge, a signal frequency, or a digital code.

[0041] It is further understood that the force sensitive unit can comprise more than two force-sensitive elements, as presented in the embodiment of the invention shown in FIG. 7, which is a perspective view of the multi-component force-torque sensor with the force sensitive unit 403 comprising three force-sensitive elements 705, 710, and 715 attached to the base 401 in such a way that the directions of the maximum force sensitivity of all force-sensitive elements are parallel to each other and to the direction of the applied force Fz and perpendicular to the base 401. A sensor cross-talk reducing member 720 interconnects the force sensitive unit 403, the torque sensitive unit 405, and the holder 402 via the force translating twisting adapter and the torque translating adapter in such a way that the force Fz can be translated from the holder to the force-sensitive elements without affecting or disturbing the torque sensitive unit, and the torque Tz can be translated from the holder to the torque sensitive unit without affecting or disturbing the force sensitive unit, thus reducing the cross-talk between the force and the torque measurements in the sensor device. In the preferred embodiment, the force-sensitive elements of the force sensitive unit attached to the base symmetrically relative to the torque sensitive unit. Similarly, the torque sensitive unit 405 can comprise multiple torque-sensitive elements connected in such a way that the direction of the maximum torque sensitivity of each torque-sensitive element coincides with the direction of the applied torque.

[0042] Another aspect of the invention illustrated in FIG. 8, wherein the force sensitive unit 803 comprises a single force-sensitive element 810 having a toroidal or a doughnut-like shape, such as a ring load cell or a load washer, attached to the base 401 concentrically relative to the torque sensitive unit 405. A sensor cross-talk reducing member 820 interconnects the force sensitive unit 803, the torque sensitive unit 405, and the holder 402 via the force translating twisting adapter and the torque translating adapter in such a way that the force Fz can be translated from the holder to the force sensitive unit without affecting or disturbing the torque sensitive unit, and the torque Tz can be translated from the holder to the torque sensitive unit without affecting or disturbing the force sensitive unit, thus reducing the cross-talk between the force and the torque measurements in the sensor device. It is understood that the torque sensitive unit can also have a toroidal shape and be attached to the base concentrically relative to the force sensitive unit comprising a single force-sensitive element.

[0043] Still another aspect of the present invention provides a method for measuring forces and torques, the method comprises a step of providing a multi-component force-torque sensing device including a mounting base, a test specimen holder, a force sensitive unit, a torque sensitive unit, and a sensor cross-talk reducing member interconnecting the test specimen holder, the force sensitive unit, and the torque sensitive unit via respective adapters in such a way that the force applied to the holder can be translated from the holder to the force sensitive unit without affecting or disturbing the torque sensitive unit, and the torque applied to the holder can be translated from the holder to the torque sensitive unit without affecting or disturbing the force sensitive unit; the method further including: a step of attaching the force-torque sensing device to a mechanical tester having a platform, a loading unit, a rotary drive, a first test specimen, and a second test specimen; a step of coupling the first test specimen to the force-torque sensing device and the second test specimen to the rotary drive; a step of causing a relative movement between the first test specimen and the second test specimen while applying a loading force to the loading unit thus developing the friction torque between the first and the second specimens and causing output signals of the force sensitive unit and of the torque sensitive unit under effect of the loading force and the friction torque; and a step of measuring the output signals in terms of the loading force and the friction torque, respectively.

[0044] The invention has been described and illustrated in various aspects with reference to specific structures and drawings. It is understood, however, that these structures and drawings are given only as examples and should not be construed as limiting the area of application of the invention. Therefore, any changes and modifications are allowed provided that they do not depart from the scope of the attached claims. For examples, more than two force-sensitive elements can be used. The mounting base may have a shape different from a flat. The adapters may have different shapes and designs, and the sensor device of the invention may be used not necessarily on a tribometer but on any other apparatus where simultaneous measurement of force and torque is needed. It is understood that features in accordance with various aspects can be used in various combinations. For examples, the force translating twisting adapters as thrust or angular contact bearings can be combined with the torque translating adapters as bellows, spider couplings, slotted-disc couplings, or as other devices suitable for accomplishing the objects of the invention within the scope of the claims.