JPH0321838A - Temperature compensating circuit for force sensor - Google Patents

Abstract

PURPOSE:To enable accurately temperature compensation over a wide range by forming temperature detecting elements whose characteristics vary linearly and curvedly with temperature on the surface of the strain dead zone part of a single-crystal plate. CONSTITUTION:On the surface of the strain dead zone of an Si substrate 6 which is the single-crystal substrate, a P-N diode 22 as the temperature detecting element which varies in characteristics linearly with temperature and a diffusion resistance 23 as the temperature detecting element varying curvedly are formed and then connected to constant current sources 24 and 25 respectively. Then voltages for temperature compensation are obtained from those detecting elements 22 and 23 and put together to perform the temperature compensation. Consequently, a characteristic curve is compensated over a wide range to perform the accurate temperature compensation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to temperature compensation of force sensors used in, for example, force sensors for robots, three-dimensional input devices as man-machine interfaces, three-dimensional load measuring devices, etc. Regarding circuits.

Conventional technology First, we will outline the overall configuration of a conventional force sensor.
This will be explained based on FIG. 8 and FIG. 19.

The center of the strain body l is the acting part 2, and this acting part 2
The surrounding area is a support portion 3. The acting portion 2 is composed of a thin diaphragm 4, and a force transmitting body 5 is formed downward from the center of the diaphragm 4. Further, a Si substrate 6 as a single crystal substrate is adhesively fixed on the diaphragm 4 of the strain-generating body 1, and a detection surface 7 of the Si substrate 6 has a diaphragm 4 in each axis direction (X, Y, Z). A strain detection element 8 is formed to detect force component force.

Further, a temperature detection element 10 is formed in a strain-insensitive area 9 (hatched area) around the detection surface 7 where the strain detection element 8 is formed.

In the force sensor configured in this way, the force transmitting body 5
When a force is applied to the diaphragm 4, the diaphragm 4 is deformed, and this deformation also deforms the single crystal substrate 6, so that stress is applied to the strain detection element 8 formed on this surface by bridge connections in each axial direction, and as a result, The component force of the force is detected by the output voltage of the bridge circuit.

Each of the strain detection elements 8 connected in this way has a temperature characteristic, and if the temperature characteristics between these strain detection elements 8 differ even slightly, the difference is outputted from the bridge circuit by a change in their resistance value. This will result in erroneous detection as voltage. Therefore, in order to compensate for the temperature characteristics of the strain detection element 8 against such temperature changes and obtain a stable output voltage at all times, the temperature detection element 1o as described above is provided.

Therefore, an example of a temperature compensation circuit using such a temperature detection element 10 will now be described based on Japanese Patent Laid-Open No. 59-153-117. In FIG. 20, Ra. Rb is a temperature detection element with large temperature dependence, and Ra, R1, and R2
Let the combined resistance of Rb, R3, and R4 be Rα, and R5, R6, Rα, and Rβ constitute a bridge circuit. Connection point P of this bridge circuit
．． Q is connected to the operational amplifier 11, and an output voltage ■α is obtained from this output side. Therefore, resistors R1 to R4
By setting the op amp 1 to an appropriate value,
The output voltage ■Ω of 1 has a temperature characteristic that cancels out the slope of the temperature characteristic and the curve of the temperature characteristic in the output voltage Vin obtained by bridge-connecting the strain detection element 8 (see FIG. 18), Thereby, temperature compensation of the strain detection element 8 is performed by obtaining the output voltage Vo of the operational amplifier 12.

Problems to be Solved by the Invention In the case of the conventional example shown in FIG. 20 as described above, R1 to
By adjusting R4, the slope of the linear component and the curvature of the quadratic curve with respect to temperature of the temperature compensation voltage VQ can be adjusted to obtain the optimum characteristics for zero point temperature compensation of the bridge circuit formed by the strain detection element 8. I'm trying to get it.

However, in this case, the method of temperature compensation is based on the diffusion resistance Ra.
Changes in resistance value of Rb with respect to temperature and fixed resistance R1
~Since R4 is simply connected, VQ is only possible within a narrow range.
Characteristics cannot be adjusted. That is, R1 to R
Since I was trying to create the compensation voltage VQ only by adjusting step 4,
It is not possible to deal with a wide range of zero point temperature characteristics as shown in FIG.

Furthermore, in the case of a temperature compensation circuit as shown in FIG. 20, since the component force of the force detected by the force sensor is multi-component, as many amplifier circuits and temperature compensation circuits as the number of component forces are required. For example, when trying to detect a three-component force, two diffused resistors Ra and Rb are required for one component force, so a total of 3×2=6 temperature detection elements are required.

Therefore, the number of diffused resistors (strain detection elements 8) formed on the Si substrate 6 increases, resulting in a problem that the chip itself cannot be miniaturized.

On the other hand, as another example in which temperature compensation is performed when obtaining an output voltage by bridge-connecting the strain detection element 8,
There is one disclosed in Japanese Patent No. 1564. this is,
Temperature compensation is performed so that the indicated value of the blood pressure monitor does not change due to fluctuations in offset voltage due to temperature changes, decreases in output sensitivity, etc.

FIG. 2l shows its configuration, and includes a stable current power supply section consisting of a transistor l4, an operational amplifier l5, a constant voltage diode 16, etc., for stabilizing the power supply to the bridge-connected diffusion type semiconductor pressure transducer 13. 17 and
This figure shows a stable amplifier circuit section 20 that is a combination of a high input impedance circuit 18 and an offset voltage correction circuit 19.

In this case, a zero point compensation resistor 13a is connected in the bridge circuit of the diffusion type semiconductor pressure transducer 13, and its zero point is adjusted by the potentiometer 21. If the zero point output of the bridge-connected diffusion type semiconductor pressure transducer 13 is larger than the output span, the output Vo in the final differential stage will be saturated to the power supply voltage due to the zero point output, and as a result, temperature compensation must be performed accurately. becomes difficult.

Means for Solving the Problem Therefore, in order to solve such problems, claim l
In the described invention, a strain-generating body is provided, with one of the center portion and the peripheral portion serving as a support portion and the other portion serving as an action portion, and a strain-sensing element that changes electrical resistance by mechanical deformation is provided on the surface of the strain-generating body. In a force sensor in which a single crystal substrate formed with is adhesively fixed, a temperature detection element whose characteristics change linearly with temperature and a temperature detection element whose characteristics change curvedly with respect to temperature are provided on the surface of the strain-insensitive part of the single crystal substrate. A temperature sensing element was formed.

In the invention according to claim 2, a strain-generating body is provided in which one of the center portion and the peripheral portion is a supporting portion and the other is an acting portion, and the electrical resistance is changed by mechanical deformation on the surface of this strain-generating body. In a force sensor in which a single crystal substrate on which a strain detection element is formed is adhesively fixed, a temperature detection element whose characteristics change linearly with temperature and a curved line are provided on the surface of the strain insensitive part of the single crystal substrate. A temperature compensation voltage generation circuit is provided which forms temperature detection elements whose characteristics change and generates a voltage for temperature compensation of the sensor output based on the voltage detected by these temperature detection elements. A zero-point temperature compensation circuit was provided to compensate for the zero-point temperature of the sensor output based on the output voltage obtained by the voltage generation circuit. Further, zero point temperature compensation circuits were provided in a number corresponding to the number of component forces of the force detected by the force sensor.

In the invention recited in claim 1, since temperature detection elements whose characteristics change linearly and curvedly with respect to temperature are respectively formed, the temperature compensation voltage obtained by these two types of temperature detection elements is combined. By performing temperature compensation over a wide range, the characteristic curve can be compensated over a wide range.

In the invention according to claim 2, the temperature compensation voltage is generated by the temperature compensation voltage generation circuit, this voltage is sent to the zero point temperature compensation circuit, and the zero point temperature compensation circuit performs zero point temperature compensation of the sensor output. Accurate force component force outputs that do not include zero point output can be obtained within the operating temperature range. In addition, by providing zero-point temperature compensation circuits in a number corresponding to the number of force components to be detected, the number of temperature detection elements for temperature compensation in a force sensor for multi-component force detection can be increased. It can be detected accurately without any interference.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 16. The overall configuration of the force sensor has been explained in the prior art (see FIG. 18), so the explanation here will be omitted, and the same parts will be denoted by the same reference numerals.

As shown in Figures 1 and 2, S as a single crystal substrate
On the surface of the strain-insensitive portion 9 of the i-substrate 6, there is a PN diode 22 as a temperature detection element whose characteristics change linearly with temperature, and a diffused resistor 23 as a temperature detection element whose characteristics change in a curve. are formed respectively. In this case, the PN diode 22 has a P-type diffusion region as an anode and a Si
The substrate 6 is used as a cathode, and constant current sources 24 and 25 are connected to the PN diode 22 and the diffused resistor 23, respectively, and are driven by these. In addition, as shown in FIG. 3, the PN diode 22 and the diffused resistor 23 are
A temperature compensation voltage generation circuit 26 that generates a temperature compensated output voltage is connected. Further, as shown in FIG. 4, the temperature compensation voltage generation circuit 26 is connected to a zero point temperature compensation circuit 27. This circuit 27 is provided with a zero point compensation circuit 28, and further includes one component of the force detected by bridge-connecting the strain detection element 8 in the force sensor of FIG. 1 (see FIG. 16). (here,
Input terminals 29a and 29b to which output voltages VXo+ and Vxo- in the X-axis direction are sent are provided.

In such a configuration, first, a description will be given based on the temperature compensation voltage generation circuit 26 shown in FIG. PN diode 2
No. 2 has a characteristic that its forward voltage drop Vd changes linearly with temperature at a slope of -2.5 mV/° C., as shown in FIG.

Further, the diffused resistor 23 has a characteristic that its voltage drop Vr changes in a curved manner that is a combination of a straight line and a quadratic curve, as shown in FIG. Then, the voltage Vd detected by the PN diode 22 is input to the amplifier 30, and the voltage Vd detected by the PN diode 22 is input to the amplifier 30, and
By varying V, the output voltage (bias component) at the reference temperature (usually 25°C) is removed, and the output voltage V
The output characteristics of dt are shown in Figure 9 when the output voltage at 25°C is O.
Adjust so that it becomes V. Furthermore, the voltage Vdt is inverted and amplified by an amplifier 31 and adjusted to have the characteristics shown in FIG. On the other hand, the voltage Vr detected by the diffused resistor 23 is input to the amplifier 32, and VR2, VR
By adjusting V.3. The output voltage (bias component) at 25°C of r is removed, and the linear component is also removed using Vdt, so that the output characteristic of the output voltage Vrt of the amplifier 32 becomes a curved characteristic as shown in FIG. Adjust so that Furthermore, the voltage Vrt is inverted and amplified by an amplifier 33 and adjusted to have the characteristics shown in FIG.

Next, the zero point temperature compensation circuit 27 shown in FIG. 4 will be explained. ±Vdt and ±Vrt created as described above are input to input terminals provided on both sides of variable resistors VR4 and VR5 in this circuit 27, respectively. At this time, Vdt is
By adjusting VR4, it is possible to freely set the temperature characteristic within the range of a = b in Fig. 13. Similarly, by adjusting VR5, Vrt can be freely set within the temperature characteristic range between d and e in FIG. 4. Then, by combining Vdt and Vrt with the amplifier 34, the output voltage VT is
A temperature-dependent voltage can be obtained by freely setting the slope of a straight line or the curvature of a quadratic curve with respect to temperature. As a specific example of this, for example, as shown in FIG.
A characteristic having a curve obtained by combining waveform C in the figure and waveform f in FIG. 14 can be obtained.

Thereafter, the voltage VT thus obtained is sent to the negative terminal of the amplifier 35 together with the zero point output compensation voltage VO obtained from the zero point compensation circuit 28 at the reference temperature (here, 25° C.). This zero point output compensation voltage Vo is
In addition to being input to , it is also input to the negative terminal of amplifier 36 . In addition, the positive terminals of these amplifiers 35 and 36 are connected to one-component force (for example, in the Output voltages (Vxo, Vxoj are input. In this case, the voltage V between amplifier 35 and amplifier 36
xo is as shown below.

R1 +-(VO -VT)...(1) R. R, B=- R6 Vx (F, T) = Vxo+- Vxo-, then Vxo = Vx (F, T) A 10B (Vo -V
T) ...-(1) is transformed.

However, T: temperature ('C), F: acting force (g), Vx (0.25): output voltage Vx when F=Og at T=25℃ (zero point output at 25℃) = Output voltage Vx when F=O at T℃ (zero point output when T''C) Vx (0, T), A・Vx (0.25) = −BVo ・=
(2) A-Vx(0,T)-A”Vx(0.25)=
If the condition BVT = (3) is satisfied, Vxo in equation (1) is O■ at 25° C., and the temperature dependence of the zero point output disappears.

Therefore, now, by transforming equations (2) and (3), A Vo Vx (0.25) ・= (4) B VT = {Vx (0, T) - Vx (0.2
5))-(5)B By adjusting the values of VR6 for VO and VR4 and VR5 for VT,
The influence of temperature dependence of zero point output can be eliminated. Then, by inputting the Vxo obtained in this way to the amplifier 37 at the next stage, one component force (in the X-axis direction) can be obtained from the output Vx.

Here, a specific example of the method of calculating the component force of the temperature-compensated force by performing the zero-point temperature compensation described above will be described in comparison with a conventional example. Now, for example, if A-10, B=1 and Fs is the rated force, then Vx (-Fs, 25) - Vx (Fs, 25) =
lomV (bridge output span for rated force)
Vx (0.25) = 20mV 22, the required span at the output Vx is 10■, Ao
Assuming that the amplification degree of the amplifier 37 is Vx=10=l O X I O−'XAXAo, Ao=1
Only 00 is required.

As a result, if zero point correction is not performed in the stage including the amplifiers 35 and 36, Vx at this time becomes 20V. In order to correct this 20 cm with the circuit of the prior art (see Fig. 21), the voltage Vp generated by the potentiometer 21 must be reduced by 20 cm.
It is necessary to adjust to V. However, since the operational amplifier (such as the operational amplifier 35) normally uses a ±15V power supply, such a voltage of 20V cannot be obtained, and the output Vx remains saturated.

On the other hand, in the method according to the present invention, from equation (4), 1, (zero point output at 25° C.) = −0.2 (V) . . . (6) may be satisfied. This -〇. 2■, it can be obtained using the power supply voltage of a normal operational amplifier. Therefore, as a result, the output Vx is not saturated and the zero point correction can be performed sufficiently. Note that although the zero point correction has been described so far, compensation for the zero point temperature characteristics can be performed in the same way.

Furthermore, in this embodiment, a case has been described in which one component force in the X-axis direction is detected, but in addition to this, when the number of component forces to be detected increases,
7 may be arranged in the number corresponding to the increased component force. Therefore, no matter how many force component forces are detected, the number of temperature detection elements 22 and 23 formed on the surface of the strain-insensitive portion 9 of the single crystal substrate 6 (see FIG. 1) is increased. It is not necessary, and the number may remain two as in the embodiment described above.

Next, a modification of the temperature compensation voltage generation circuit 26 and the zero point temperature compensation circuit 27 in the above-described embodiment will be described. First, a modification of the temperature compensation voltage generating circuit 26 shown in FIG. 5 will be described. This circuit 26, as shown in FIG. ±Vdt and ±Vrt are not created by removing the components. Therefore, these bias components are converted to Vdt.
After combining Vrt, it is removed together with the zero point output Vx (0.25) by the output Vo of the zero point compensation circuit 28. Moreover, in this case, adjustment is performed using VR4 and VR5 so that VT has an appropriate slope of a linear component.

Next, a modification of the zero point temperature compensation circuit 27 shown in FIG. 4 will be described. This is the sum of V(it, Vrt and the output Vx
This is a modification of the circuit configuration for determining o. in this case,
Using the relationship of equation (1), Vxo is calculated as follows: + − (Vrt −Vdt) − (7)R,

Since Vrt and Vdt can be combined from the second term of equation (7), appropriate temperature compensation can be performed. In addition, in such a circuit, the amplifier 34.38
Although it is not possible to correct Vx (0.25), the Vo of the zero point compensation circuit 28 is
By inputting the value, Vx (0.25) is corrected, thereby making it possible to perform optimal temperature compensation with zero point correction.

Effects of the Invention The invention according to claim 1 forms temperature detection elements whose characteristics change linearly and curvedly with respect to temperature, so that the temperature compensation voltage obtained by these two types of temperature detection elements is By performing temperature compensation through synthesis, characteristic curves can be compensated over a wide range.

In the invention as claimed in claim 2, the temperature compensation voltage is generated by the temperature compensation voltage generating circuit, and the temperature compensation voltage is sent to the zero point temperature compensation circuit, so that the temperature compensation voltage and the zero point compensation circuit are used to generate the temperature compensation voltage. Since temperature compensation has been performed, it is possible to accurately detect force component forces that have undergone zero point compensation and zero point temperature compensation.

In addition, since it is sufficient to provide a number of zero point temperature compensation circuits corresponding to the number of component forces of the force to be detected, it is possible to increase the number of temperature detection elements for temperature compensation in a force sensor for detecting multiple force components. It is possible to perform temperature compensation accurately without any problems.

[Brief explanation of drawings]

FIG. 1 is a plan view of a force sensor showing an embodiment of the present invention;
Fig. 2 is a vertical side view showing the wiring state of the temperature detection element part, Fig. 3 is a circuit diagram showing the temperature compensation voltage generation circuit, Fig. 4 is a circuit diagram showing the zero point temperature compensation circuit, and Fig. 5 is a circuit diagram showing the temperature compensation voltage generation circuit. Figure 6 is a circuit diagram showing a modification of Figure 3, Figure 6 is a circuit diagram showing a modification of Figure 4, Figure 7 is a characteristic diagram showing the temperature characteristic curve of a PN diode, and Figure 8 is a diagram showing a temperature characteristic curve of a PN diode. A characteristic diagram showing the temperature characteristic curve, Fig. 9 is a characteristic diagram showing the state after removing the bias voltage of the voltage in Fig. 7, and Fig. 10 is a characteristic diagram showing the state when the voltage in Fig. 9 is inverted and amplified. Figure 11 is the 8th
Figure 12 is a characteristic diagram showing how the voltage shown in Figure 11 is inverted and amplified after the bias voltage is removed, Figure 13 is a characteristic diagram showing how the voltage in Figure 11 is inverted and amplified, and Figure 13 is adjusted using the characteristic curve in Figure 9. 14 is a characteristic diagram showing various modifications when the resistance value of the resistor is changed, FIG. 14 is a characteristic diagram showing various modifications when the resistance value is changed in the characteristic curve of FIG. 11, and FIG. Characteristic diagram showing the state of the waveform formed by combining the characteristic curves in FIGS. 13 and 14, 1st
Figure 6 is a circuit diagram showing an equivalent circuit when the strain detection elements formed on the surface of the single crystal SL substrate in Figure 1 are bridge-connected;
Fig. 17 is a characteristic diagram showing zero point temperature characteristics, Fig. 18 is a plan view showing the configuration of a conventional force sensor, Fig. 19 is a side view thereof, and Figs. 20 and 21 are diagrams showing the conventional zero point temperature compensation. FIG. 3 is a circuit diagram showing the mechanism. DESCRIPTION OF SYMBOLS 1... Strain body, 2... Action part, 3... Instruction part, 6...
. . . Single crystal substrate, 8 . . . Strain detection element, 9 . , 28・
...Zero point compensation circuit applicant Rico Co., Ltd.

Claims (1)

[Scope of Claims] 1. A strain-generating body is provided, with one of the center portion and the peripheral portion serving as a support portion and the other portion serving as an action portion, and the electrical resistance is changed by mechanical deformation on the surface of this strain-generating body. In a force sensor in which a single crystal substrate on which a strain detection element is formed is fixed with adhesive,
A temperature sensor characterized in that a temperature detection element whose characteristics change linearly with respect to temperature and a temperature detection element whose characteristics change curvedly with respect to temperature are formed on the surface of the strain-insensitive part of the single crystal substrate. Compensation circuit. 2. A strain-generating body is provided with one of the center portion and the peripheral portion serving as a support portion and the other portion serving as an action portion, and a strain detection element is formed on the surface of this strain-generating body to change electrical resistance by mechanical deformation. In a force sensor in which a single crystal substrate is adhesively fixed,
A temperature detection element whose characteristics change linearly with temperature and a temperature detection element whose characteristics change curvedly with respect to temperature are formed on the surface of the strain-insensitive part of the single crystal substrate, and the voltage detected by these temperature detection elements is A temperature compensation voltage generation circuit is provided to generate a voltage for temperature compensation of the sensor output based on
A temperature compensation circuit for a force sensor, comprising a zero point temperature compensation circuit that performs zero point temperature compensation of the sensor output based on the output voltage obtained by the temperature compensation voltage generation circuit. 3. The temperature compensation circuit for a force sensor according to claim 2, further comprising a number of zero point temperature compensation circuits corresponding to the number of force components detected by the force sensor.