EP3762680A1

EP3762680A1 - Measuring mechanical changes

Info

Publication number: EP3762680A1
Application number: EP19708090.6A
Authority: EP
Inventors: Gernot Nitz
Original assignee: KUKA Deutschland GmbH
Current assignee: KUKA Deutschland GmbH
Priority date: 2018-03-05
Filing date: 2019-02-27
Publication date: 2021-01-13
Also published as: US20210372870A1; WO2019170483A1; DE102018203251A1; CN111819416A; DE102018203251B4; US11549855B2

Abstract

A device for measuring mechanical changes comprises at least one first resistor, which is designed to convert a mechanical change into an adjustment of its resistance value; and at least one operational amplifier, wherein the at least first resistor and the operational amplifier are connected such that the at least first resistor serves the operational amplifier as an input resistance and the operational amplifier provides or can provide a measurement result at an output. The first resistor is e.g. a strain gauge which can be secured on a component.

Description

Measuring mechanical changes

The present invention relates to measuring mechanical changes. For this purpose, the invention provides a device, an arrangement, a use and a method.

It is already known from the prior art to use strain gauges (or strain gauges, abbreviated DMS) for measuring mechanical changes, for example of a component. From the prior art it is known to use DMS interconnected in a Wheatstone bridge circuit. For example, in a full bridge one would use two opposing strain gauges whose resistance changes (due to mechanical changes) with a positive sign are included in the measurement result, and two opposing strain gauges whose resistance changes with a negative sign are included in the measurement result.

The inventor of the present invention has recognized that such circuits are of limited use for various applications.

The object of the present invention is to improve the measurement of mechanical changes and / or to make them more flexible.

This object is achieved by a device having the features of claim 1. Claims 15, 18 and 19 protect an assembly, a use and a method. The subclaims relate to advantageous developments. Further developments, which are explicitly claimed or described, for example, only for the device, apply correspondingly also to the arrangement, the use and the method.

According to an embodiment of the present invention, there is provided an apparatus for measuring mechanical changes

at least one first resistor adapted to convert a mechanical change into a change in its resistance value; and

at least one operational amplifier,

wherein the at least one first resistor and the operational amplifier are connected such that the at least one first resistor is connected to the operational amplifier Input resistance is used and the operational amplifier at an output delivers or can deliver a measurement result.

Although the use of already known Wheatstone bridge circuits for measuring mechanical changes often also an operational amplifier is used, the resistance, which implements in such known circuits a mechanical change in a change in its resistance value, not as input resistance for the operational amplifier. Instead, in such circuits, the inputs of the operational amplifier are switched to the so-called Messdiagonale.

By the above-proposed embodiment of the invention, a large number of circuit options can be realized, which would not be possible with a conventional bridge circuit. These will be explained in more detail in the following text.

In one embodiment, the first resistor is a strain gauge. As is known to those skilled in the art, strain gages change their ohmic resistance when stretched, for example, in a mechanical change experienced by a component to which they are attached. Alternatively, however, the first resistor may also be an inductive resistor or a capacitive resistor. While embodiments of the present invention will be explained below mainly by means of a DMS, the invention is not limited to the use of DMS.

According to one embodiment, the first resistor is fastened or attachable to a component such that a mechanical change of the component can bring about or bring about the change in the resistance value of the at least first resistor.

In particular, when using a strain gauge, the strain gauge would typically be mounted on a surface of the component such that the length of the strain gauge changes with a mechanical change of the component.

In one embodiment, the mechanical change of the component on a change in a dimension in at least one dimension and / or bending and / or torsion of the component. A change of a dimension in at least one dimension is to be understood here in particular as meaning, for example, that the length of the component (for example a rod) changes, to which the first resistor is attached. This is stretched by it. Even with a bend or torsion (again, for example, a rod), depending on the attachment of the first resistor to the component, an elongation of the first resistance may result.

In particular, in the case of a torsion, it is preferably a torsion about an axis. In order to detect such torsion, the first resistor may be attached to the device in a particular manner: at least a portion of the first resistor will respond to a change in resistance in a first direction (e.g. The first resistor is then preferably attached to the component such that this first direction subtends an angle x with a parallel to the axis of torsion, where 0 <x <90 degrees, preferably 10 degrees <x, more preferably 30 degrees < x, more preferably 40 degrees <x and / or preferably x <80 degrees, more preferably x <60 degrees, more preferably x <50 degrees.

In one embodiment, a first electrical connection of the first resistor (or in the case of the use of a plurality of resistors, in each case a first electrical connection of the resistors) is coupled to an input of the operational amplifier. A second electrical terminal of the first resistor (or resistors) is provided to be electrically coupled (each) to an input electrical voltage. By applying appropriate input voltage (s), the resistor (s) can be individually "turned on" or "off". Also, the various resistors can be weighted differently by suitable input voltages.

In one embodiment, the device is set up to measure different, in particular different, mechanical changes of the component by changing the respective input voltage for the at least first resistor.

In this way - especially when using multiple resistors - different mechanical changes of the component can be measured, so for example a bend not only about an axis, but about different axes, or a change in length not only in one dimension but in several dimensions, or a torsion not only about one axis / in one direction, but about several axes and / or in several directions. Likewise, various mechanical changes of the component can be measured, not only individually For example, a change in length or a bend or a twist, but more of these types of mechanical changes.

In one embodiment, the input voltage for the at least first resistor may be fed back to infer from the value of the applied input voltage and the value of the returned voltage to the voltage actually applied to the at least first resistor. This allows more accurate measurements. This will be particularly noticeable when relatively long cables (e.g., several meters long, several tens of meters, or over 100 meters long) are used to connect the first resistor to its input voltage.

According to one embodiment, the device has a DA converter for providing the respective input voltage for the at least first resistor. This allows a particularly user-friendly choice of the input voltage for each resistor.

According to one embodiment, the device has a shunt resistor, which is connected in parallel with the at least first resistor or can be switched. This can be used to calibrate the circuit.

According to one embodiment, the device has at least 2, preferably at least 3, more preferably at least 4, further preferably at least 8, 12 or 16 resistors, wherein the resistors are connected in parallel and serve as input resistors for the operational amplifier. In principle, it is possible to use an arbitrarily large number of resistors as input resistors for the operational amplifier.

By using several resistors different mechanical changes can be measured (almost) simultaneously.

In one embodiment, the device is set up to be operated in a measuring mode, wherein in measuring mode, in each case two input voltages are applied to two of the resistors, which are substantially equal in magnitude, but of opposite polarity. As a result, some disturbing influences, such as changes in temperature, can be largely eliminated.

In one embodiment, the device is set up to be operated in a first test mode, wherein in the first test mode, only one of the resistors has an input voltage that is different from ground, and the input voltage is grounded on all other resistors.

This can be tested to see if this one resistor is present / functional. Such a test can be performed successively for all resistors.

In one embodiment, the device includes an additional test resistor that may be connected in parallel with the at least first resistor, wherein the device is configured to operate in a second test mode, wherein in the second test mode, an input voltage different from ground is applied only to the test resistor and on all other resistors, the input voltage is grounded, and wherein in measurement mode, the input voltage for the test resistor is grounded.

In this second test operation, for example, the functionality of the operational amplifier can be checked. In normal measurement mode, the test resistor would have no significant impact on the measurement result, because applying ground as input voltage to the test resistor will "turn it off".

In one embodiment, the device comprises at least two resistors and in a first (amplification) stage two operational amplifiers, at least one of the at least two resistors serving as input resistance to the two operational amplifiers and the outputs of the two first stage operational amplifiers electrically connected to inputs, respectively a third operational amplifier, the third operational amplifier representing a second (amplification) stage and supplying or delivering a measurement result at an output.

As a result, some disturbing influences, such as common-mode voltages at the inputs (eg mains humming), can be suppressed. According to one aspect of the present invention, there is provided an apparatus for measuring mechanical changes, comprising: a component; and one of the devices described above, wherein the at least first resistor is attached to the component, preferably glued.

In order to achieve a reliable mechanical connection between the component and the resistor, the resistor is preferably attached flat to a surface of the component, for example glued. Thus, the forces that occur during a mechanical change of the component and transferred to the resistor, spread over the entire contact area between the component and resistor.

In one application, the component has a 6D force-moment sensor with multiple measurement spokes, each measurement spoke being provided with a plurality of resistances of the measurement device.

In another application example, the component has a flex spline of a Harmony Drive transmission.

In another aspect, the invention relates to the use of a resistor configured to convert a mechanical change into a change in its resistance as an input resistance to an operational amplifier.

In another aspect, the invention relates to a method of measuring mechanical changes, comprising:

Providing one of the above-described arrangements;

Supplying the at least first resistor with an input voltage; and

Outputting a measurement result at the output of the operational amplifier.

Further advantages and features emerge from the exemplary embodiments. This shows, partially schematized: Fig. 1: a circuit according to an embodiment of the present invention;

2 shows an arrangement of resistors on a component after a

Embodiment of the present invention;

3 shows a circuit for use with embodiments of the present invention;

4 shows an arrangement of resistors on a component after a

Embodiment of the present invention;

5 shows an arrangement of resistors on a component after a

Embodiment of the present invention;

Fig. 6 shows a circuit according to an embodiment of the present invention;

Fig. 7: a circuit according to an embodiment of the present invention;

8 shows a circuit according to an embodiment of the present invention;

9 shows a circuit according to an embodiment of the present invention;

10 shows a circuit according to an embodiment of the present invention;

Fig. 1 1: an arrangement of resistors on a component according to an embodiment of the present invention;

12 shows an arrangement of resistors on a component after a

Embodiment of the present invention;

Fig. 1 shows a circuit according to an embodiment of the present invention. The measuring circuit 10 has a bipolar-fed operational amplifier 1 with an inverting input 2, a non-inverting input 3 and an output 4. The non-inverting input 3 is at ground (0V). A node 7 of the circuit 10 is coupled (directly) to the inverting input 2. At the exit 4 the output voltage U_off can be removed. A resistor RO is electrically (directly) coupled to the output 4 and the node 7. Also coupled to the node 7 is at least one input resistor - in the example shown four input resistors R1, R2, R3 and R4. For the first input resistor R1, a first electrical connection 5 is indicated, which is electrically coupled (directly) to the node 7. The input resistors are each electrically (directly) connected to an input voltage U1, U2, U3 and U4. For the first input resistance R1, a second electrical connection 6 is indicated, which is electrically coupled (directly) to the input voltage U1. Further input resistors could be connected in a corresponding manner parallel to the illustrated resistors R1 to R4.

The circuit of Figure 1 with only one operational amplifier 1 can be regarded as a single-stage amplifier circuit. The value of the negative feedback resistance R0 in relation to the input resistors R1 to R4 determines the gain.

The following applies: U_off = - U1 (R0 / R1) - U2 (R0 / R2) - U3 (R0 / R3) - U4 (R0 / R4)

The circuit thus sums the ratio of R0 to Ri (i = 1, 2 ...), each weighted by the corresponding input voltage.

In this embodiment of the invention, the resistors R1 to R4 are not fixed resistors, but strain gages. Thus, the circuit can be used to detect mechanical changes that cause changes in the resistance of the strain gages, because a change in the resistance values of the resistors R1 to R4 affects the output voltage U_out.

The input voltages may be provided, for example, by a DA converter.

In experiments carried out by the inventor, good results could be achieved if strain gauges were chosen for resistors R1 to R4, whose resistance values are approximately equal, eg 350 W. However, one can also mix different strain gauges. By the magnitude and the sign of the input voltages LH to U4, the weighting and the sign of the change of the resistors R1 to R4 can be controlled individually. By adding DMS, the effect of the change in resistance of the DMS used on the output signal can be increased as desired. For a Wheatstone bridge this is not possible beyond the four basic bridge resistances. If, for example, two strain gauges per branch bridge are connected in series in a Wheatstone bridge, the resistance change has been doubled with the same strain of the two strain gages in a bridge branch, but since the total resistance is also doubled, the same influence on the output voltage of the bridge results as with individual strain gauges in the bridge branch. Parallel connection of strain gages in the bridge branch results in similar conditions.

Particularly good results can be achieved with the measuring circuit 10 of FIG. 1, if at least some, and preferably all, strain gages have an "antagonist". A counterpart to a first DMS is preferably a second DMS, which is connected to an opposite, approximately the same input voltage as the first DMS. This can be used in particular to minimize thermal drifts: Resistance changes of a first DMS due to temperature changes are compensated by corresponding resistance changes of a second DMS.

The wire lengths of two wired as counterparts DMS are preferably about the same to choose, so that temperature changes cause no offset of the output voltage. The role of the opponent is not fixed but can be redistributed in successive measurements by changing the polarity of the input voltages between the DMSs involved. In the exemplary embodiment of FIG. 1, for example, in a first measurement R1 may be the opponent of R2 and R3 may be the antagonist of R4. In a second measurement, by changing the input voltages, the R1 can take on the role of the opponent of the R3 and the R2 the counterpart of the R4.

As a variant of the embodiment of FIG. 1, one could also use a fixed resistor as the counterpart of a DMS. Preferably, however, is taken into account that fixed resistors change their resistance depending on the temperature under certain circumstances differently, in particular change significantly different, as DMS, which in their meager stretching on a material (ie the material of the component, on which DMS is attached) can match. Overall, a fixed resistor can be expected as an opponent to a DMS with larger drifts.

Due to the individually adjustable input voltages, the strain gauges can generally be individually weighted. As a variant to an equal (but opposite) weighting of a DMS and its counterpart, it would be possible to choose an unequal weighting by different input voltages. This can be used to achieve certain effects, e.g. to consider asymmetrical geometries of a component. For example, if a change in length of a pipe having circumferentially different wall thicknesses is to be measured by an arrangement according to Figure 1, it may be useful to have a first strain gauge attached to a first pipe section having a first wall thickness different from a suitable input voltage to weight as a second DMS, which is attached to a second pipe section with a second (different from the first wall thickness) wall thickness. Preferably, however, the weights are also similar here, for example with a deviation of at most 3%, 5% or 10%, in order to limit thermal drifts to an acceptable level.

Fig. 2 shows an arrangement of resistors (DMS) on a component according to an embodiment of the present invention. On a round rod (or tube) 15, which is indicated in cross section, four strain gauges (SG 1 to SG 4) are evenly distributed around the circumference of the rod. In this example, the strain gages are attached longitudinally to a surface of the rod. The DMS are preferably connected flat to the surface of the rod, for example, glued to the rod. A change in length of the portion of the rod to which a DMS is attached, causes a change in length of the corresponding DMS and thus a change in the resistance value of the DMS, which can be evaluated according to the figure 1.

By dashed lines, two axes 20, 21 are indicated in Figure 2, around which the rod 15 can bend. If you switch the strain gauges 1 and 4 with positive weighting and the DMS 2 and 3 with negative weighting measures the bending moment about the axis 20. In turn, you measure the bending moment and the axis 21, if the DMS 3 and 4 positive weights and the DMS 1 and 2 negative. This change in weighting can be done by simply changing the sign of the input voltages applied to the respective DMS. In a variant (not shown) could attach the DMS similar to Figure 2, but alternately obliquely at an angle of 45 ° to about 80 ° to the longitudinal axis of the rod. Thus, with appropriate input voltages, it is not only possible to measure the bending about the axes 20 and 21, but also the torsion about the longitudinal axis of the rod. An angle greater than 45 ° can be used to reduce the modulation of the measuring amplifier in the torsion measurement in relation to the deflection in the bending measurement. Alternatively, one could vary the amount of input voltages depending on the measured variable.

In principle, angles between 0 ° and 90 ° can be selected. Useful angle values can be determined empirically for each application. In many cases, the angles will be between 10 ° and 80 °, or between 30 ° and 60 °, or between 40 ° and 50 °. For example, the angle may be substantially 45 °.

For the signs of the input voltages, the following table could be used:

With successive switching of the input voltages U1 to U4, one would successively receive electrical voltages proportional to the desired measured variables at the output 4 of the amplifier 1.

Depending on the components used, for example, bilateral CMOS switches can be used to switch the input voltages. Preferably, these are used with downstream impedance transformers. An example of such an impedance converter is shown in FIG. 3, the CMOS switch being indicated by reference numeral 17. Two different input voltages U1 a and U1 b are applied to the inputs of the CMOS switch. An output of the CMOS switch is coupled to a non-inverting input of an operational amplifier 18 (this operational amplifier 18 is not to be confused with the operational amplifier 1 of FIG. 1). An output 19 of the operational amplifier 18 is connected in a manner known per se to the inverting input of the operational amplifier 18 fed back. In addition, the output 19 serves as an input voltage U1 for the strain gauge 1 (or R1) of FIG. 1.

The indicated in Fig. 3 switching can be made, for example, with a frequency of several tens of kilohertz, which is sufficient for the quasi-simultaneous measurement of mechanical variables in many cases.

The separation of the measured quantities at the output 4 (FIG. 1) can take place by AD conversion of the output voltage U_out of the measuring amplifier, if appropriate after a certain settling time respectively after switching over the input voltages of the strain gauges. The control of the CMOS switches, the AD converter and a digital output interface (not shown) as well as a processing of the measurement data in physical units can take place via a microcontroller (not shown) integrated in the sensor. In general, the user would not notice the rapid switching of the input voltages of the strain gauges in practical measuring mode. In other words, the user would typically feel that the various measurements (bending about different axes, torsion, etc.) are essentially simultaneous and output / displayed at the same time.

FIG. 4 shows a further example, which is based on the example of FIG. A portion of the surface of the rod 15 is shown as a surface on which two strain gages 30, 31 are arranged perpendicular to each other. DMS 30 is arranged along the longitudinal direction of the rod 15 ("linear"). DMS 31 is arranged transversely to the longitudinal direction of the rod 15.

The arrangement of Figure 4 can be used for the measurement of the bending moments and the tensile / compressive force on the round bar 15. It makes sense to use three or four such groups, which are arranged distributed at 120 ° or 90 ° on the circumference of the rod. For the measurement of tension / compression or bending linear / transverse to different planes, the signs (input voltage) for the weighting of the strain gauges can be selected as follows, for example:

Another variant is shown in FIG. Figure 5 shows the surface (or portion of the surface) of the rod 15 on which four pairs of strain gauges are arranged. Each pair has a respective DMS 33, 35, 37, 39 transversely to the longitudinal direction of the rod 15 and a respective DMS 32, 34, 36, 38 which is inclined with respect to the longitudinal direction of the rod 15 by an angle between 0 ° and 90 ° , For example, about 45 ° (see also the variant of Figure 2 with respect to the possible angle). The inclined DMS are alternately inclined in one or the other direction, so DMS 32 and 36 to the right and DMS 34 and 38 to the left.

With such an arrangement, the bending moments in two planes, the tensile / compressive force and the torsional moment, which acts on the rod 15, measure. The weights of the strain gauges can be chosen as follows:

The evaluation of measurement results using a circuit according to FIG. 1 will now be considered in more detail. With, for example, four input resistors R1 to R4, as already mentioned:

U_off = - U1 (R0 / R1) - U2 (R0 / R2) - U3 (R0 / R3) - U4 (R0 / R4) For example, if you want to use R3 as the opponent to R1 and use R4 as the opponent to R2, and Furthermore, if the input voltages are all the same in magnitude, but for opponents of opposite polarity, one could write: U1 = U2 = U on and U3 = U4 = -U on

In addition, consider a case in which all resistors have the same resistance value R in the ground state (that is, without strain). In the case: Ri = R + ARi (i = 1..4)

Where ARi is the strain-induced change in the resistance of the resistor Ri. This results in

U_off / U_ein = - R0 / (R + AR1) - R0 / (R + AR2) + R0 / (R + AR3) + R0 / (R + AR4).

If one chooses for the negative feedback resistance RO = R shown in FIG. 1, one can approximately write:

U_off / U_ein = + AR1 / R + AR2 / R - AR3 / R - AR4 / R

It should be noted that the deviation caused by the approximation to an exact calculation is only about 0.0008% for strain gages with 350 W and a distortion caused by the strain of 1 W. This deviation is usually much smaller than the expected measurement accuracy.

By selecting RO, the overall gain can be selected. If, for example, RO = 35 kD for the negative feedback resistance and R = 350 W as the resistance value of the strain gage instead of RO = R, a gain of 100 would result.

Instead of (temporarily) constant input voltages and ohmic input resistors, it is also possible to use alternating voltages as input voltages to e.g. switch on inductive or capacitive input resistors. In the case of an inductive resistor, a mechanical change would typically affect the inductive resistance such that a ferromagnetic core pushes into or is at least partly pulled out of a coil of the inductive resistor, resulting in a change in its resistance value. For a capacitive resistor, a change in its resistance would typically be caused by changes in the spacing of two plates of a capacitor of the capacitance due to mechanical changes.

When using inductive or capacitive input resistors, however, a conflict of interest between the AC frequency and the switching frequency of the weights of the input voltages may arise. In addition, the phase shifts require a certain amount of time for a sign change of the weights, since inductive or capacitive measuring resistors are more susceptible to oscillations As ohmic strain gages, they have resistances that can be switched within the range of the possible slew rates of the impedance transformers, for example within a few microseconds.

In the circuit of Figure 1, another advantage of the circuit comes into play. It is in fact possible to switch on individual strain gauges (for example, only one strain gage) in a test mode (ie, as a rule without mechanical change of the strain gauge) by applying an input voltage different from ground (0V) and shutting off all others (OV). By measuring the voltage U_out actually present at the output 4 of the operational amplifier 1 and comparing it with the expected output voltage, it is possible to determine whether the input resistance switched on is operationally or correctly connected. If a deviation outside a specified or specified tolerance, it can be concluded that the input resistance is not functional or not connected correctly. This test can be performed successively for other resistors of the circuit. Thus, the integrity of the measuring arrangement can be checked. Because the input resistors can be switched on and off relatively quickly if necessary, this test can be carried out in a relatively short time. This is particularly advantageous for a large number of connected DMS.

Further developments of the circuit presented in FIG. 1 will now be described with reference to FIGS. 6 to 10.

The single-stage circuit of FIG. 1 represents a basic circuit which does not suppress common-mode voltages at the inputs (eg mains hum). In order to enable common-mode rejection, a two-stage circuit according to FIG. 6 can be used. This circuit again comprises, in a first (amplification) stage, an operational amplifier 1 with a negative feedback resistor ROa and input resistors. In the example shown, only two input resistors R1 and R2 are connected to the inverting input of the operational amplifier 1 and corresponding input voltages U1 and U2. The circuit can also have other input resistors. In a corresponding manner, the circuit has a second operational amplifier 100, to which in turn a negative feedback resistor ROa and input resistors R3 and R4 are connected. The second operational amplifier 100 is also part of the first (amplification) stage. The outputs of the operational amplifiers 1 and 100 are respectively connected via resistors R5 to the inverting and non-inverting inputs of a third operational amplifier 200, which constitutes a second (amplification) stage. Whose output is connected via a further negative feedback resistor ROb to the inverting input of the third operational amplifier 200. The non-inverting input of the third operational amplifier 200 is connected to ground (0V) via a further resistor ROb. At the output of the third operational amplifier 200, the output voltage U_aus can be removed.

Thus, in the circuit of FIG. 6, two input amplifiers 1, 100 are used for two DMS groups. The difference of the output signals is then formed and amplified in a further stage.

Instead of the differential amplifier 200 shown in Fig. 6, the second stage gain can also be realized by a fully integrated instrument amplifier whose gain is set with only a single external resistor.

FIG. 7 shows a variant of the circuit of FIG. 1. The input voltages U1 to U4 are fed back via sensor lines and can then be measured as returned voltages U1 S to U4S. Such a circuit may be used, in particular, for relatively long cables between the voltage source (s) providing the input voltages U1 to U4 and the input resistors R1 to R4. Likewise, this circuit is used with increased demands on the accuracy of measurement. In this circuit, it is assumed that the voltage losses in the cable from an input voltage source (Ui) to the corresponding input resistance (Ri) are about as large as the voltage losses in the corresponding feedback sensor line. Accordingly, the mean value between the (applied) input voltage Ui and the returned sensor voltage UiS can be assumed to be actually applied to the input (in the figure on the left) input 6 of an input resistor Ri. The measured value display of the measuring amplifier can be corrected accordingly.

FIG. 8 shows a further circuit variant based on the circuit of FIG. 1. In Figure 8, a shunt resistor 40 is additionally used, which can be connected in parallel by a switch 41 to a DMS (here R1). When switch 41 is closed the result is a defined detuning of the measuring circuit, ie when the shunt resistor 40 is switched on, the output voltage U_out makes a jump. On the basis of the measured value of this jump and of the (known in advance) resistance value of the shunt resistor 40, a calibration of the measuring amplifier or a test of the circuit for correct function can be carried out.

FIGS. 9 and 10 show a further circuit variant based on the circuit of FIG. 1. FIGS. 9 and 10 additionally show a test resistor 42 (R test). This can be supplied via a switch 43 with an input voltage. The switch 43 connects the test resistor 42 either to a test voltage U_test (FIG. 9) or to ground (0V, FIG. 10). The test resistor 42 is also connected to the node 7 and thus also to the inverting input of the operational amplifier 1.

In a test mode, shown in FIG. 9, (only) the test resistor 42 is connected to an input voltage different from ground. All other input resistors R1 to R4 are grounded with their inputs. In particular, the correct operation of the operational amplifier 1 can be checked in this test mode.

In order to use the circuit for the normal measuring operation, as shown in Figure 10, the input of the test resistor 42 by the switch 43 is grounded. The other input resistors R1 to R4 can then be connected to their respective ground different input voltages. The test resistor then does not (essentially) affect the measurement, so that the circuit behaves as in FIG.

FIG. 11 shows an application example of the present invention. The 6D force-moment sensor 50 has a central tool hub 54 connected to four measuring spokes 56. At their outer ends, the measuring spokes 56 are each connected to a central region of a leaf spring 58. The sensor also has four housing screw 52 points. The four leaf springs 58 extend between the Gehäuseanschraubpunkten 52. At each measuring spoke 56 a plurality of DMS 60 are arranged. In the example shown, two strain gages 60 are located on each measuring spoke 56 on the visible side of the arrangement, each strain gauge 60 being inclined by approximately 45 ° to a center line of the measuring spoke 56. On each measuring spoke 56 is a DMS 60 inclined to the right and a DMS 60 to the left. Overall, therefore, eight DMS 60 are arranged on the visible side of the arrangement. In addition, located on the invisible, the observer side facing another eight DMS 60 in a corresponding or similar arrangement, a total of sixteen DMS 60th

The DMS 60 of two adjacent measuring spokes each form their own 6D sensor. This creates two redundant 6D sensors.

With the arrangement shown in FIG. 11, forces and / or moments in the measuring spokes can be measured by the strain gages 60 when the middle tool hub 54 moves relative to the housing screw-on points 52. The measurements can be evaluated by the circuits described above.

With the sensor 50, the bending moments in two planes, the torsional moment and the forces in three coordinate directions can be measured in each case.

Figure 12 shows another application example of the present invention. FIG. 12 shows, in a simplified representation, a Harmony Drive transmission 70 or a part thereof. Immediately on the flexspline 72 of the transmission 70, four strain gauges 74 are mounted in two DMS groups that can be used for torque measurement. Within one group, the two strain gages 74 are rotated by 90 ° with respect to each other. In the present example, the DMSs 74 of a group are arranged crosswise. The two groups are offset from each other by 90 ° in the circumferential direction of the Flexspline 72. Two DMS 74 (one of each group) are thus aligned in the circumferential direction. These are in the circumferential direction perpendicular to the other two DMS 74th

Each two circumferentially aligned DMS 74 can be evaluated by corresponding input voltages of opposite sign to each perpendicular thereto two other strain gages. However, due to the complex deformation of the Flexspline, interference harmonics with twice and four times the rotational frequency of the wave generator of the Harmonie Drive gearbox can be created. To compensate for these interfering harmonics, one can weight the DMS 74 differently in a fixed time sequence. The strength of the compensation can be adjusted by the duration of the weighting and / or by the magnitude of the weighting. For example:

The weighting with the opposite sign of strain gages 1 and 2 as well as strain gages 3 and 4 (first line of the table) produces measuring signals which are proportional to the applied torque for a fixed period of time.

The weighting with the same sign of the strain gauges 1 and 2 or 3 and 4 (second and third line of the table) produces measurement signals that are proportional to the noise components for an adjustable short period of time.

By choosing the time duration of the two compensation components, the interference harmonics can be largely removed or significantly reduced in the mean value of the temporal overall signal course.

In addition to this compensation by averaging, a compensation after digitization of the measured useful and interference components is possible by computational means.

Preferably, the switching takes place rapidly in relation to the desired bandwidth of the useful signal and to the engine rotational frequency, e.g. in the range of several kilohertz. Furthermore, it is recommended to use thin strain-compensated strain gauges adapted to the material of the Flexspline for this process.

Although exemplary embodiments have been explained in the foregoing description, it should be understood that a variety of modifications are possible. It should also be noted that the exemplary embodiments are merely examples that are not intended to limit the scope, applications and construction in any way. Rather, the expert is given by the preceding description, a guide for the implementation of at least one exemplary embodiment, with various changes, in particular with regard to the function and arrangement of the components described made without departing from the scope of the invention as it results from the claims and these equivalent combinations of features.

Bezuaszeichenliste

1 operational amplifier

2 inverting input of the operational amplifier

3 non-inverting input of the operational amplifier

4 output of the operational amplifier

5 first electrical connection of an input resistor

6 second electrical connection of an input resistor

7 node

10 measuring circuit

15 rod / tube / component

17 CMOS switches

18 operational amplifier of an impedance converter

19 output of the operational amplifier of the impedance converter 20, 21 first and second axis (bending)

30-39 strain gauges (DMS)

40 shunt resistance

41 switches

42 test resistor

43 switches

50 sensor

52 housing screw-on points

54 Tool hub

56 measuring spokes

58 leaf spring

60 strain gages

70 Harmony Drive gearbox

72 flex splines

74 strain gages

100 operational amplifiers (first stage)

200 operational amplifiers (second stage)

Claims

claims

A mechanical change measuring apparatus (10) comprising: at least one first resistor (R1) configured to convert a mechanical change into a change in its resistance value; and at least one operational amplifier (1),

wherein the at least first resistor (R1) and the operational amplifier (1) are connected such that the at least first resistor (R1) serves as an input resistance to the operational amplifier (1) and the operational amplifier supplies a measurement result (U_out) at an output (4) or can deliver.

2. Device according to claim 1, characterized in that the at least first resistor is a strain gauge, an inductive resistor or a capacitive resistor.

3. Apparatus according to claim 1 or 2, characterized in that the first resistor is fixed or attachable to a component (15) such that a mechanical change of the component causes or can bring about the change in the resistance value of the at least first resistor.

4. The device according to claim 3, characterized in that the mechanical change of the component (15) has a change of a dimension in at least one dimension and / or a bending and / or a torsion of the component,

wherein, in the event of torsion, the torsion is preferably torsional about an axis, wherein at least a portion of the at least first resistance reacts with a change in resistance value to a mechanical change of that portion in a first direction, the at least first resistance being secured to the component is that this first direction includes an angle x with a parallel to the axis of torsion, where 0 <x <90 degrees, preferably 10 degrees <x, more preferably 30 degrees <x, more preferably 40 degrees <x and / or preferably x <80 degrees, more preferably x <60 degrees, more preferably x <50 degrees.

5. Device according to one of the preceding claims, characterized in that in each case a first electrical terminal (5) of the at least first resistor (R1) is electrically coupled to an input (2) of the operational amplifier (1) and a second electrical terminal (6) of the at least first resistor (R1) is provided to be electrically coupled to an electrical input voltage (U1).

6. Apparatus according to claim 5 as a function of claim 3 or 4, characterized in that the device (10) is adapted by a change in the respective input voltage (U1) for the at least first resistance different, in particular different, mechanical changes of the component (15) to measure.

7. Apparatus according to claim 5 or 6, characterized in that the input voltage (U1) for the at least first resistor (R1) is returned to from the value of the applied input voltage (U1) and the value of the recirculated voltage (U1 S) to close the voltage actually applied to the at least first resistor.

8. Apparatus according to claim 5, 6 or 7, characterized in that the device comprises a DA converter for providing the respective input voltage for the at least first resistor.

9. Device according to one of the preceding claims, characterized in that the device has a shunt resistor (40) which is connected in parallel with the at least first resistor (R1) or can be switched.

10. Device according to one of the preceding claims, characterized in that the device has at least 2, preferably at least 3, more preferably at least 4, more preferably at least 8, 12 or 16 resistors (Ri), wherein the resistors are connected in parallel and as Input resistors for the operational amplifier (1) are used.

1 1. Apparatus according to claim 10, characterized in that the device is adapted to be operated in a measuring operation, wherein abut in measuring operation on two of the resistors pairwise input voltages which are substantially equal in magnitude, but of opposite polarity.

12. The apparatus of claim 10 or 1 1, characterized in that the device is adapted to be operated in a first test operation, wherein in the first test operation only at one of the resistors of a ground different input voltage is applied and at all other resistors Input voltage is grounded.

13. The apparatus of claim 10, 1 1 or 12, characterized in that the device comprises an additional test resistor (42) which is connected in parallel to the at least first resistor or can be switched, wherein the device is adapted for, in a second Test operation to be operated, wherein in the second test mode, a ground different input voltage applied only to the test resistor and on all other resistors, the input voltage to ground, and wherein in measurement operation, the input voltage for the test resistor is grounded.

14. Device according to one of the preceding claims, characterized in that the device has at least two resistors and in a first stage, two operational amplifiers (1, 100), wherein in each case at least one of the at least two resistors is the two operational amplifiers as input resistance and wherein the Outputs of the two first-stage operational amplifiers are electrically coupled to inputs of a third operational amplifier (200), respectively, and the third operational amplifier provides or can provide a measurement result (U_out) at an output.

15. Arrangement for measuring mechanical changes, comprising:

a component (15); and

a device (10) according to any one of the preceding claims,

wherein the at least first resistor (R1) is fixed to the component, preferably glued.

16. Arrangement according to claim 15, wherein the component has a 6D force-moment sensor (50) with a plurality of measuring spokes (56), wherein each measuring spoke is provided with a plurality of resistors (60, Ri) of the measuring device (10).

17. Arrangement according to claim 15, wherein the component has a flex spline (72) of a Harmony Drive transmission (70).

18. Use of a resistor (Ri), which is adapted to convert a mechanical change in a change in its resistance value, as input resistance for an operational amplifier (1).

19. A method of measuring mechanical changes, comprising:

Providing an arrangement according to claim 15, 16 or 17;

Supplying the at least first resistor (R1) with an input voltage (U1); and

Outputting a measurement result (U_out) at the output (4) of the

Operational amplifier (1).