Device and method for calibrating and testing a torque transducer

Abstract

Device for testing and calibrating a torque transducer (1) comprising a measuring flange with sensor elements and a printed circuit board (5) connected to the measuring flange with sensor electronics, wherein the device comprises: - a unit (7) for generating defined torques; - a reference sensor (8); - a measuring device (21) designed to interact with the sensor electronics; characterized by - a buttress (16); - a drive element (13) configured to connect the reference sensor (8) to the torque transducer (1) rotationally via a positive fit; and - a pressure element (23) which is designed to apply a defined pressure force to the torque transducer (1) in the axial direction relative to the abutment (16) while forming a force-fit connection.

Description

[0001] The present invention relates to a device for calibrating and testing a torque transducer and a method for calibrating and testing such a torque transducer.

[0002] Torque transducers detect torques, for example, via an elastic deformation of a deformable body of this transducer and / or measure a torque using a measured quantity proportional to this torque.

[0003] As sensors, these must be calibrated appropriately before use, which can be done statically or quasi-statically. Calibration is generally performed by introducing known torques into the torque measurement chain, usually separately for clockwise and counterclockwise torques. In comparison methods with reference torque transducers, calibration is typically performed continuously, i.e., quasi-statically, over time with discrete torque values. Such calibration methods are well known.

[0004] Up to now, the calibration of torque transducers, which are used, for example, in drive units of articulated robots, as described, for example, in the applicant's German patent application DE 10 2016 004 787 A1, has always taken place in the assembled state of the drive unit, which is cumbersome and hinders automation.

[0005] Furthermore, the torque measurement chain in the drive unit extends over a large number of components.

[0006] Other torque transducers are known, for example, from CN 2 10 774 494 U, CN 2 07 408 028 U and CN 1 09 932 126 A.

[0007] The invention is directed in particular, but not exclusively, to torque transducers used in drive units of articulated robots, preferably compliance-controlled lightweight robots. Such a torque transducer is known, for example, from German patent application DE 10 2016 012 324 A1 of the applicant. This transducer consists of a measuring flange with an outer flange ring and an inner flange ring, wherein the outer flange ring and the inner flange ring are connected by equidistantly arranged measuring spokes designed to deform elastically under the influence of a torque and which have sensor elements in the form of strain gauges, the strain gauge elements of the measuring spokes being interconnected via corresponding bridge circuits. A printed circuit board is arranged on an end face of the measuring flange, which has correspondingly designed sensor electronics.The connections of the strain gauges, which are usually glued onto the measuring spokes, may be soldered to the sensor electronics.

[0008] The present invention aims to create more efficient ways to calibrate and test torque transducers, in particular torque transducers of the type mentioned above.

[0009] This problem is solved with a device having the features of claim 1 and with a method having the features of claim 14.

[0010] In a first aspect, a device for calibrating and testing a torque transducer is proposed, which has a measuring flange with sensor elements and a printed circuit board connected to the measuring flange with sensor electronics, wherein the device comprises: - a unit for generating defined torques; - a reference sensor; - a measuring device designed to interact with the sensor electronics; - a buttress; - a drive element designed to connect the reference sensor to the torque transducer rotationally via a positive fit; and - a pressure element designed to apply a defined pressure force to the torque transducer in the axial direction relative to the abutment, forming a force-fit connection.

[0011] The torque transducer is therefore coupled to the body of the reference sensor in a torque-transmitting manner and then subjected to a defined pressure. The unit for generating defined torques, which can be of any design, introduces defined torques into this connection, resulting in elastic deformations at the torque transducer.

[0012] The advantage according to the invention lies in the fact that the combination of positive locking between torque transducer and drive element on the one hand and force locking between torque transducer and pressure element or the abutment, such as a support plate, on the other hand prevents uneven clamping of the torque transducer.

[0013] In one embodiment of the invention, the drive element, which can be designed in any way but has at least such stiffness that error-free torque transmission is enabled, includes the measuring device.

[0014] This measuring device is preferably designed as a plate that can be screwed to a flange ring of the drive element. It has contact pins arranged relative to the torque transducer such that these measuring points are opposite the sensor electronics, forming an electrically conductive connection. These contact pins make simple contact with the measuring points. When the torque transducer is inserted into the device, the tips of the contact pins touch the measuring points. This proves to be extremely low-wear and also allows for automation when calibrating multiple torque transducers, since a plug connection to the external calibration or evaluation control does not have to be established each time, resulting in considerable time savings.

[0015] A further advantage of the invention lies in the fact that the measuring device is interchangeable. This allows torque transducers with differently configured circuit boards, and therefore different measuring points, to be tested in the device. Accordingly, measuring devices can then be used and connected to the drive element where the contact pins are positioned at corresponding locations.

[0016] In one embodiment of the device according to the invention, the unit for generating defined torques is directly connected to the reference sensor, preferably screwed together by means of adjacent flange rings to form a continuous torque measuring chain.

[0017] As already mentioned, the invention is preferably directed towards torque transducers, such as those described by way of example in DE 10 2016 012 324 A1, which have a measuring flange with an outer flange ring and an inner flange ring and with measuring spokes running between them, on which the sensor elements connected to the sensor electronics are arranged. According to the invention, the device is designed such that the pressure element has a hold-down device which is configured to interact only with the outer flange ring in such a way that uniform pressure forces are exerted on it around its circumference. For this purpose, the hold-down device is preferably mounted centrally via a ball joint. This ensures that the desired elastic deformation is introduced into the torque transducer as uniformly as possible.

[0018] Furthermore, the inner flange ring of such a torque transducer has a hub, and the drive element has a correspondingly designed adapter for receiving the hub, with the hub and the adapter being designed such that a torque-transmitting connection between them is formed exclusively by a positive fit. A snap-fit ​​connection would be conceivable for this purpose, for example.

[0019] As already mentioned, this realizes a significant advantage of the device according to the invention, namely that the combination of positive locking and force locking between the two mutually movable components, the torque transducer and the abutment, which can be designed as a support plate to be explained below, prevents uneven clamping of the torque transducer.

[0020] The device can further comprise a housing configured to receive the reference sensor and the drive element in the axial direction, wherein the housing of the unit for generating defined torques has a receiving device for the torque transducer opposite it. The upper end or adapter of the drive element and the contact needles of the measuring device project into the receiving device.

[0021] According to the invention, the pressure element is pivotably mounted relative to the receiving device such that automatic loading of the receiving device with torque transducers is enabled, e.g., by means of suitable robots. These robots are programmed to place the torque transducers with their hub onto the adapter of the drive element in such a rotational orientation that the contact pins are opposite the corresponding measuring points on the circuit board of the torque transducer. The dimensions of the receiving device and the drive element with the adapter are determined in coordination with the torque transducer such that, when the positive locking is fully established, the contact pins simultaneously form a low-wear electrical contact with the measuring points, achieved through simple touch.

[0022] In a further embodiment of the device according to the invention, the receiving device is designed to receive the abutment in the form of a support plate, against which the torque transducer can ultimately be clamped by the pressure element, forming a force-fit connection.

[0023] Preferably, this support plate, which forms the bearing surface for the outer flange ring, is interchangeable, making it possible to achieve different friction conditions. Different support plates allow for the easy adaptation of varying coefficients of friction, which can occur due to different materials and / or coatings of the torque transducer.

[0024] The device includes a mounting plate for attaching the support plate, which allows the support plate to be attached to the housing, preferably by screwing it in place. This means that the support plate can be easily and cost-effectively replaced when it becomes worn.

[0025] The pressure element, or the necessary drive mechanism (which can be hydraulic or pneumatic), can be connected to the housing. The mounting plate, which bolts the support plate to the housing, is designed so that the entire device, consisting of the pressure element and housing, can be attached or bolted as a single unit to an external support, such as a mounting platform. This simplifies assembly and maintenance of the device.

[0026] In a second aspect, the invention relates to a method for calibrating and testing a torque transducer, which has a measuring flange with an outer flange ring and an inner flange ring and with measuring spokes running between them, on which sensor elements connected to sensor electronics are arranged, comprising steps: - Forming a rotary connection between the inner flange ring of the torque transducer and a reference sensor; - Applying a defined pressure force to the outer flange ring of the torque sensor against a support; - gradual or continuous application of nominal torques to the torque sensor via the reference sensor; - Measuring the torque values ​​of the reference sensor; - Measuring the torque values ​​of the sensor elements of the torque transducer, which result proportionally from the elastic deformation of the measuring spokes; - Comparing the measured torque values ​​with predefined limit values; - Determining calibration parameters according to a predefined algorithm; - Storing the resulting calibration parameters in the sensor electronics; indicating the further steps: - Applying test torques to the torque transducer via the reference sensor; - Measuring the torque values ​​of the sensor elements of the torque transducer, which result proportionally from the elastic deformation of the measuring spokes; and - Comparing the measured torque values ​​with limit values ​​modified by the previously determined calibration parameters.

[0027] Static and quasi-static calibration methods for torque transducers relative to a reference sensor are well known. In these methods, the input variable (reference torque(s)) and the output variable (measured torque(s) as a function of elastic deformation) are determined by series of measurements with respect to the signal-related slopes and intercepts, and then compared to each other, e.g., typically using the least-squares method, before the values ​​can be entered into the measurement or evaluation system (i.e., the sensor evaluation electronics) of the torque transducer.

[0028] The device according to the invention offers the advantage that a torque transducer calibrated in this device can be checked immediately after the calibration steps to verify whether the calibration parameters stored in the sensor electronics ensure proper functioning of the torque transducer. In other words, it is verified, while the torque transducer remains in the device, whether the torques measured as a response to the applied test torques, taking the calibration parameters into account, correspond to the reference torques of the reference sensor.

[0029] The invention proposes, after calibration, to apply corresponding test torques or a sequence of test torques to the torque sensor via the reference sensor and the drive element, and then to measure the torque values ​​of the sensor elements of the torque transducer, which result proportionally from the elastic deformation of the measuring spokes, via the measuring device, and subsequently to compare the measured torque values ​​with the limit values ​​of the sensor electronics modified by the previously determined calibration parameters.

[0030] Ideally, a successful calibration would be characterized by the fact that at each measurement point, the torque values ​​of the torque transducer and the reference sensor would be identical, i.e., the value of the slope would be 1 and the value of the center distance would be 0.

[0031] Verification of functionality and thus of a previously successful calibration would then be characterized by the fact that, after completion of the measurement series with the test torques, the slope would be almost at a value of 1 and the center distance would be almost at a value of 0.

[0032] According to the invention, the measurement series can be carried out analogously to the calibration measurement series by gradually increasing the defined test torques to a maximum value and performing several measurements during this process, each time while the machine is at rest. This can be done accordingly in both directions of rotation.

[0033] The method according to the invention can further include the additional step of verifying the hysteresis behavior of the torque sensor by comparing the behavior of the torque sensor at identical measurement times with increasing test torques to the behavior with decreasing test torques.

[0034] The subsequent testing procedure within the device, which, as part of the automated calibration, is performed solely on the torque sensor, simultaneously detects any defects in the torque sensor components, such as in the contacts, solder joints, or the electronic components themselves. In contrast to the prior art, the calibration and subsequent testing phase take place at the torque sensor level before it is installed in the drive unit for a joint of an articulated robot arm.

[0035] Further features and advantages of the present invention will become apparent from the description of the exemplary embodiment illustrated with reference to the accompanying figures. These show: Fig. 1 schematically an exploded view of the device according to the invention; Fig. 2a a cross-sectional view through the device in the closed state; Fig. 2b a cross-sectional view through the device in the open state; Fig. 3a schematically a perspective view of the device in the closed state; Fig. 3b schematically a perspective view of the device in the open state; Fig. 4a a first part of a flowchart of the method according to the invention, which represents a preload phase; Fig. 4b a second part of a flowchart of the method according to the invention, which represents a calibration phase; and Fig. 4c a third part of a flowchart of the method according to the invention, which represents a testing phase.

[0036] In the Fig. Figures 1 to 3b show the device for testing and calibrating a torque transducer with all its components and in the two operating states.

[0037] In the embodiment shown, the device serves to calibrate and test a torque transducer 1, such as that known from DE 10 2016 012 324 A1 of the applicant.

[0038] This torque transducer 1 consists of a measuring flange with an outer flange ring 2 and an inner flange ring or hub 3, between which measuring spokes 4 run, on which strain gauges (not shown) are arranged. A circuit board 5 with corresponding sensor evaluation electronics is provided below the measuring flange.

[0039] The device has a housing 6, to the underside of which a drive unit 7 is attached, which serves to generate defined torques and can be designed as desired.

[0040] The housing 6 serves to accommodate a body of a reference sensor 8, which is rotationally fixed to the unit 7 for generating defined torques, e.g. via a flange ring 9 and several screws 10.

[0041] The body of the reference sensor 8 is rotatably connected to a drive element 13, which is also housed in the casing 6, by means of screws 12 via an upper flange ring 11.

[0042] Opposite the drive unit 7, the housing 6 has a receiving device 14 for the torque transducer 1.

[0043] In the embodiment shown, the receiving device 14 is designed in its simplest form as a circumferential end-face partial ring surface 15, on which a support plate 16 is arranged, which in turn is screwed firmly to the housing 6 and a mounting plate 17 placed on the support plate 16.

[0044] The drive element 13 extends upwards into the receiving device 14 so far that a pin-like adapter 18 can serve, via several axial guide or locking elements 19, for the exclusively positive locking reception of the hub 3 of the torque transducer 1, while at the same time the flange outer ring 2 comes to rest on the support plate 16.

[0045] Furthermore, the drive element 13 has a circumferential shoulder 20 onto which a plate-like measuring device 21 can be screwed.

[0046] The measuring device 21 has several contact needles 22 at such points that, when the torque transducer 1 is held in the receiving device 14, they come into electrically conductive contact with the corresponding measuring points of the electronics of the circuit board 5, which is based purely on contact, as is particularly evident in the Fig. 2a can be seen.

[0047] In the housing 6, the reference sensor 8, the drive element 13 and the torque transducer 1 form a torque measuring chain in the axial direction.

[0048] A pressure element 23 can be attached to the housing 6, which has a pivotably mounted hold-down device 24 that is preferably pneumatically activated between an open position ( Fig. 2b, Fig. 3b) and a closed position ( Fig. 2a, Fig. 3a) is movable.

[0049] In the open position, the receiving device 14 can be fitted with the torque transducer 1 by hand or preferably automatically using a robot, or the torque transducer 1 can be removed from it after testing and calibration have been completed.

[0050] The pivotable hold-down device 24 is designed such that, in the closed position, it only makes contact with the outer flange ring 2 of the torque transducer 1. The hold-down device 24 is mounted via a ball joint 25, ensuring that the applied compressive force is distributed evenly over the circumference of the outer flange ring 2 and transferred via this ring to the support plate 16. This ensures that, when the torques intended for calibration are applied by the unit 7 and via the reference sensor 8 and the drive element 13 into the hub 3 of the torque transducer 1, the desired elastic deformation in the measuring spokes 4 is caused. This deformation is detected by the strain gauges and then measured via the contact needles 22 of the measuring device 21.

[0051] As in the perspective representations of the Fig. 3a and Fig. As can be seen in 3b, the device can be handled as a whole unit and can be attached to an external bracket using the mounting plate 17.

[0052] In the Fig. Figures 4a to 4c show a flowchart of the method according to the invention, wherein Fig. 4a a preload phase, Fig. 4b a calibration phase and Fig. 4c represents a verification phase.

[0053] The torque transducer 1 is inserted into the receiving device 14 of the apparatus according to the invention, either manually or by means of an automation unit, such as a compliance-controlled robot, so that the hub 3 forms a torque-transmitting connection with the adapter 18 of the drive element 13, creating a positive fit. The pressure element 23 is then pneumatically activated, and the hold-down device 24 closes and clamps the torque transducer 1 against the support plate 16 by engaging only the outer flange ring 2 (step S1).

[0054] In this position, a zero signal from the unloaded torque sensor can be measured to draw conclusions about the temporal stability of the torque sensor.

[0055] The torque transducer 1 is then subjected relatively quickly in both directions of rotation to a defined maximum torque value, usually the full-scale value of the torque to be calibrated, possibly under a compressive force exerted by the hold-down device 14 (step S2). This serves, among other things, to remove any adhesive residue that may be present between the strain gauges and the measuring spokes 4, to reduce creep of the torque transducer 1 material, and also to establish a reliable electrical and mechanical connection between the contact pins 22 and the measuring points or contacts of the sensor electronics on the circuit board 5. At this point, only the reference sensor 8 is connected to the evaluation circuit of the device, while no signals are yet being taken from the measuring device 21.

[0056] In step S3, it is checked whether the pre-loading phase was carried out correctly and completely, i.e., whether all contacts between measuring device 21 and circuit board 5 were formed, the zero signal was determined, and, if applicable, whether all strain gauges respond, which suggests that any adhesive residue present has no influence, etc. Otherwise, step S2 is repeated as often as necessary.

[0057] The system then attempts to establish a connection between the device's evaluation circuit and the sensor electronics (step S4). If this is not possible, an error signal (step E1) is output and the torque sensor 1 is removed from the device.

[0058] If this is possible, the process begins in Fig. 4b shows the calibration phase, in which the measurement series are carried out to align the torque transducer 1 with the reference sensor 8.

[0059] The torque transducer 1 is subjected to a defined pressure force by means of the hold-down device 24 and the torque transducer 1 together with the reference sensor 8 is subjected to slowly increasing, defined nominal torques due to the rotary connection via the drive element 13 (step S5) in order to cause the elastic deformations in the measuring spokes 4.

[0060] The individual torque values ​​are then measured during a steady state (the applied torque remains constant at the time of measurement) for both the torque transducer 1 and the reference sensor 8 (step S6). Ideally, six measurements are performed for each direction of rotation.

[0061] In a subsequent step S7, it is checked whether all desired nominal torques have been applied and all measurements have been successfully carried out. If this is not the case, the procedure is repeated again with step S5 as many times as necessary.

[0062] If this is the case, the slope and the center distance, i.e. the calibration parameters, are calculated from the measured values ​​taking into account a predefined algorithm (e.g. a least-squares function) and any channels resulting from the bridge circuits between the individual strain gauges (step S8).

[0063] Then, in step S9, it is checked whether these values ​​are within the specified limit ranges. If this is not the case, an error message is displayed (step E2).

[0064] However, if these are within the specified limit ranges, the calibration parameters are written to the sensor electronics (step S10).

[0065] The calibration of the torque sensor 1 is complete, and it could now be removed from the device for installation in the corresponding drive unit. However, the method according to the invention is further extended by a verification phase, which is carried out in the Fig. Figure 4c shows the procedure used to verify whether, taking into account the previously calculated calibration parameters, the torque behavior of the torque transducer 1 corresponds to that of the reference sensor 8, at least within certain predefined limit ranges. The torque transducer 1 remains in the device for this purpose.

[0066] For this purpose, the torque transducer 1 and the reference sensor 8 are again subjected to slowly increasing test torques via their rotary connection through the drive element 13 (step S11), and the torque values ​​are measured in different steady-state conditions (test torque is unchanged at the time of measurement) (step S12). In step S13, it is checked whether all measurements were successful; otherwise, step S11 is repeated.

[0067] Using predefined algorithms (e.g., the least-squares function), the corresponding slope and center distance are calculated and checked to ensure that, for each measurement time, the calibrated torque transducer 1 and the reference sensor 8 output the same torques. This means that for the determined measurement curves, the slope value must be 1 and the center distance value 0 (step S14). The actual check is performed taking predefined limits into account; that is, the slope should be close to 1 and the center distance close to 0. If this is not the case, an error message is issued (step E3), and the calibrated torque transducer 1 is classified as faulty and therefore rejected.

[0068] If this is the case, the hysteresis behavior of torque sensor 1 is then checked, i.e., the behavior of torque sensor 1 at the measurement times during increasing test torques in relation to decreasing test torques (step S15). If these values ​​are not within the corresponding limit ranges in relation to a predefined maximum value, an error message (step E4) is issued and torque sensor 1 is classified as defective.

[0069] If the hysteresis behavior is deemed acceptable, the hold-down device 24 is opened and the torque sensor 1 can be removed for subsequent installation in a drive unit of the device (step S16).

[0070] The advantage of the method according to the invention lies in the fact that it allows for the automation of both calibration and functional testing at the sensor level. Thus, a faulty torque sensor 1 can be rejected before it is installed in a drive unit, whereas in the prior art, calibration and functional testing of the torque sensor were only performed in its installed state, i.e., in relation to the entire torque measurement chain of the drive unit. A faulty torque sensor already installed in this system would always result in the entire drive unit becoming inoperable, or it would have to be disassembled again, which incurs considerable costs in both cases.

Claims

[1] Device for testing and calibrating a torque transducer (1) having a measuring flange with sensor elements and a printed circuit board (5) connected to the measuring flange with sensor electronics, the device comprising: - a unit (7) for generating defined torques; - a reference sensor (8); - a measuring device (21) which is designed to interact with the sensor electronics; characterized by - an abutment (16); - a driver element (13) which is designed to connect the reference sensor (8) to the torque transducer (1) in a rotational manner via a positive connection; and - a pressure element (23) which is designed to apply a defined pressure force to the torque transducer (1) in the axial direction relative to the abutment (16) while forming a frictional connection. [2] Device according to claim 1, wherein the driver element (13) comprises the measuring device (21). [3] Device according to claim 2, wherein the measuring device (21) has contact needles (22) which are arranged relative to the torque transducer (1) such that these measuring points are opposite the sensor electronics, forming a conductive connection. [4] Device according to claim 2 or 3, wherein the measuring device (21) is replaceable. [5] Device according to one of claims 1 to 4, wherein the unit (7) for generating defined torques is directly connected to the reference sensor (8). [6] Device according to one of claims 1 to 5, in which the torque transducer (1) has a measuring flange with a flange outer ring (2) and a flange inner ring (3) and with measuring spokes (4) running between them, on which the sensor elements connected to the sensor electronics are arranged, wherein the pressure element (23) has a hold-down device (24) which is designed to cooperate with the flange outer ring (2) in such a way that equal pressure forces are exerted on it all the way around. [7] Device according to claim 6, wherein the flange inner ring has a hub (3) and the driver element (13) has an adapter (18) for receiving the hub (3), wherein the hub (3) and the adapter (18) are designed such that a torque-transmitting connection is formed between them. [8] Device according to one of claims 1 to 7, in which a housing (6) is provided which is designed to receive the reference sensor (8) and the driver element (13) in the axial direction and which has a receiving device (14) for the torque transducer (1). [9] Device according to claim 8, wherein the pressure element (23) is pivotally mounted relative to the receiving device (14) in such a way that automatic loading of the receiving device (14) is possible. [10] Device according to claim 8 or 9, wherein the abutment is designed as a support plate (16) and the receiving device (14) is designed to receive the support plate (16), relative to which the torque transducer (1) is clamped by the pressure element (23) to form the frictional connection. [11] Device according to claim 10, wherein the support plate (16) is replaceable. [12] Device according to claim 10 or 11, wherein a mounting plate (17) is provided which fastens the support plate (16) to the housing (6). [13] Device according to claim 12, wherein the pressure element (23) is fastened to the housing (6) and both can be fastened as a unit to a holder by means of the mounting plate (17). [14] Method for testing and calibrating a torque transducer (1) having a measuring flange with a flange outer ring (2) and a flange inner ring (3) and with measuring spokes (4) extending between them, on which sensor elements connected to a sensor electronics are arranged, comprising the steps: - forming a rotational connection between the flange inner ring (3) of the torque transducer (1) and a reference sensor (8); - applying a defined compressive force to the flange outer ring (2) of the torque sensor (1) against an abutment (16); - gradually or continuously applying nominal torques to the torque sensor (1) via the reference sensor (8); - measuring the torque values of the reference sensor (8); - measuring the torque values of the sensor elements of the torque transducer (1), which result proportionally from the elastic deformation of the measuring spokes (4); - Comparing the measured torque values with predefined limit values; - Determination of calibration parameters according to a given algorithm; - Saving the resulting calibration parameters in the sensor electronics; characterized by the next steps: - applying test torques to the torque transducer (1) via the reference sensor (8); - measuring the torque values of the sensor elements of the torque transducer (1), which result proportionally from the elastic deformation of the measuring spokes (4); and - Comparing the measured torque values with limit values modified by the previously determined calibration parameters. [15] Method according to claim 14, in which the test torques are gradually increased to a maximum value and during which several measurements are each carried out during a rest state. [16] Method according to claim 15, wherein the measurements are carried out in both directions of rotation. [17] Method according to one of claims 14 to 16, comprising the further step: - Checking the torque values of the torque transducer (1) at identical measuring times with increasing test torques and with decreasing test torques

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