JPH0321839A - Force sensor - Google Patents

Abstract

PURPOSE:To enable the accurate temperature compensation of output sensitivity by a resistance for sensitivity temperature compensation by providing such a resistance insulating and separating means for sensitivity temperature compensation that the resistance for sensitivity temperature compensation is biased reverse electrically to a single-crystal substrate. CONSTITUTION:On the surface of an Si substrate 6 which is a single-crystal substrate, the resistance 10 for sensitivity compensation is formed, and on its surface, wiring patterns 171 and 17b are further formed across an insulating layer 16. A circuit 18 for sensitivity compensation consists of resistances Ra, Rb, and Rc connected in series, the patterns 17a and 17b are connected to the resistance Ra corresponding to the resistance 10, and a P-N diode 15 is formed between the resistance Ra and substrate 6. Then the composite resistance of the circuit 18 is connected between Vc and V02, so the temperature compensating resistance Ra is held at the potential between them and the resistance Ra is biased reverse to the substrate 6. Consequently, the accurate sensitivity and temperature compensation is enabled without any error.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a force sensor used in, for example, a force sensor for a robot, a three-dimensional input device as a man-machine interface, a three-dimensional load measuring device, and the like.

Conventional technology First, we will explain the general structure of a conventional force sensor.
This will be explained based on FIGS. 0(a) and (b). The center of the strain body 1 is an acting portion 2, and the periphery of the acting portion 2 is a supporting 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 a certain portion of the force. A sensitivity temperature compensation resistor 10 is formed in a strain-insensitive portion 9 (hatched portion) around the detection surface 7 on which the strain detection element 8 is formed.

Here, further consideration will be made based on the contents disclosed in Japanese Patent Publication No. 59-41134. FIG. 11(a) is a plan view showing a simplified surface state of the Si substrate 6, and FIG. 11(b) is a side view thereof. FIG. 12 also shows a bridge circuit 11 configured by connecting the distortion detection element 8, an amplifier circuit 13 configured by two amplifiers 12 connected to the output side, and furthermore, a bridge circuit 13 configured by connecting the distortion detection element 8, and an amplifier circuit 13 configured at the output stage. The state of the output circuit 14 including the connected sensitivity temperature compensation resistor 10 is shown.

In this case, the strain detection element 8 and the sensitivity temperature compensation resistor 10 are made of P-type diffused resistors, and the Si substrate 6 is made of an N-type substrate. As a result, the boundary between these resistors and the Si substrate 6 forms a PN diode 15, and the potential at point P on the Si substrate 6 side (7) is
It is approximately Vcc-0.6V.

Problem to be Solved by the Invention Therefore, at this time, the potential of the sensitivity temperature compensation resistor 10 is Vc.
If the potential does not reach c or less, the sensitivity temperature compensation resistor 1
0 and the Si substrate 6 are not in a reverse bias state. If reverse bias is not achieved, the sensitivity temperature compensation resistor 10
A forward current flows from the P-type region of the Si substrate 6 to the N-type region of the Si substrate 6, and the P-type region no longer functions as a normal resistor.
As a result, a problem arises in that temperature compensation of the output sensitivity of the sensor output value cannot be accurately performed. Also, the 12th
In the circuit configuration shown in the figure, the sensitivity temperature compensation resistor 10
is connected to the output terminal Vo, which may be larger than Vcc depending on the amount of distortion received by the bridge circuit 11 and the required output level, and the sensitivity temperature compensation resistor 10 is always connected to the Si substrate 6. A reverse bias is not always maintained between the two, and this causes the problem described above.

Furthermore, in a force detecting device filed by the present applicant in Japanese Patent Application No. 63-99061, as shown in FIG.
(See Figure 10(a))
The N diode 15 is reverse biased by a voltage of -Vd. As a result, even when the voltage vh is connected as external noise, noise countermeasures are taken by preventing the noise current In from flowing from the strain body l side to the Si substrate 6 side via the PN diode 15. There is.

In this case, since the measurement is carried out by keeping the side of the strain detection element 8 that constitutes one bridge circuit at a negative potential, the circuit configuration similar to that shown in FIG. When trying to amplify the output voltage and perform temperature compensation, unless the sensitivity temperature compensation resistor 10 is biased to the negative potential side, the sensitivity temperature compensation resistor 10 and the Si substrate 6
There is no reverse bias between That is, the output voltage Vo
It is necessary to set the voltage to the negative side. In this case, the output voltage Vo is input to a subsequent A/D converter (not shown), but normally, such an A/D converter can only handle the positive human voltage. It has become common. Therefore, even if the applicant's force detection device (see Fig. 13) is connected to such a circuit (see Fig. 12) and an attempt is made to transfer the output signal to the subsequent stage, there is a problem that it cannot be done accurately. occurs.

Means for Solving the Problems Therefore, in order to solve such problems, the present invention provides a strain-generating body in which one of the center part and the peripheral part is a support part and the other part is an action part, In a force sensor in which a single crystal substrate on which a strain detection element that changes electrical resistance by mechanical deformation and a sensitivity temperature compensation resistor are formed is adhesively fixed to the surface of the strain body, the sensitivity temperature compensation resistor is Sensitivity temperature compensation resistance insulation isolation means is provided which is electrically reverse biased with respect to the single crystal substrate.

Therefore, by setting the sensitivity temperature compensation resistor to be electrically reverse biased with respect to the single crystal substrate by the sensitivity temperature compensation resistor insulation separation means, the boundary between the sensitivity temperature compensation resistor and the single crystal substrate is set. Current leakage in the parts can be eliminated, and as a result, the output sensitivity can be accurately temperature compensated by the sensitivity temperature compensation resistor.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. The overall configuration of the force sensor has been described in the prior art (see FIGS. 10(a) and 10(b)), so a description thereof will be omitted, and the same parts will be denoted by the same reference numerals.

First, in FIG. 2, a Si substrate 6 as a single crystal substrate
A sensitivity temperature compensation resistor 10 is formed on the surface of the
Furthermore, wiring patterns 17a and 17b are formed on the surface with an insulating layer 16 in between. In this case, the Si substrate 6 is made of a material having N-type (hereinafter referred to as N-type Si substrate) characteristics, and the sensitivity temperature compensation resistor 10 is made of a P-type diffused resistor. In addition, FIG. 1 shows a sensitivity temperature compensation circuit 8 as a resistance insulation separation means for sensitivity temperature compensation according to the present invention.
1 is a circuit diagram showing the overall configuration of a sensor output detection circuit including.

Now, let's take a look at the portion of FIG. 2 that corresponds to the sensitivity temperature compensation circuit 18 of FIG. The sensitivity temperature compensation circuit 18 includes resistors Ra, Rb. It is constructed by connecting Rc in series and parallel, and the combined resistance value of these three is Rt.
shall be. At this time, the sensitivity temperature compensation resistor 10 corresponds to Ra, and wiring patterns 17a and 17b are connected to both ends of Ra. Further, a PN diode 15 is formed between Ra, which is a P-type diffused resistor, and the N-type Si substrate 6.

The overall configuration of the circuit shown in FIG. 1 will be described below.

The bridge circuit 11 constituted by the strain detection element 8 is excited by a bridge excitation voltage -Vd, and the potential at the output side signal lines 1 9 a, 1 9 b is approximately 1 Vd/2 (V). It has become. This bridge circuit 11 is connected to the first stage amplifier 20, thereby performing impedance conversion and amplification of the sensor outputs from the signal lines 19a and 19b. Now signal fil9a,1
Let the respective voltages of 9b be Va and Vb, and the first stage amplifier 2
The respective output voltages of the amplifiers 21 and 22 at V. 1,
■. 2, and when actually substituting numerical values, each voltage value is -Vd=
At -6V, when Va and Vb are subjected to strain around -Vd/2=-3V, they change by only about ±50mV at most. That is, Va, vb=-2.95 to -3.05V
within the range of

Also, the gain G of the first stage amplifier 20 is Then, R, R, =4.5 R2 becomes.

If Va=-3.05V, Vb=-2.95V, V
,,=-3,05X5.5-4.5 (-2.95)=
-3.5V ■. ,=-2.9 5X5.5-4.5 (-3.0
5) = -2.5V Thereafter, these output voltages V o++ Vex are manually inputted to the second stage amplifier 23 . This second stage amplifier 23 has
The sensitivity temperature compensation circuit 18 according to the present invention is connected, and its output voltage Vc is K3. However, if Rt/R, ξ1, then Vc=-2.5+1-(-2.5-(-3. 5) 1=
-1.5V. Also, at this time, the inverting input terminal voltage of the amplifier 24 is
One is almost equal to ■ya, and ■ya is ■. Almost equal to 2.

At this time, the resistances Ra, Rb. R
The combined resistance Rt of Vc and -2.c is -1.5V.
V. which becomes 5V. ．． Since the temperature compensating resistor Ra is connected between the two, the potential of the temperature compensating resistor Ra is naturally at a potential between these. Therefore, since Ra is in a reverse bias state with respect to the N-type Si substrate 6, normal sensitivity temperature compensation can be performed without including an error.

Also, when Va=-2.95V, Vb=-3.05V, V0,=-2.5V, V,,=-3.5V, Vc=
-4.5V, and the potential of temperature compensation resistor Ra is -
It is between 3.5V and -4.5V. Therefore, in this case as well, as in the case described above, Ra is in a reverse bias state with respect to the N-type Si substrate 6, and normal sensitivity temperature compensation can be performed.

After that, ■. 2. The output of Vc is sent to the final third stage amplifier 25
If differential amplification is performed by R. Vo = (VC V62)R, As a result, an output proportional to Va-Vb appears in Vo. In this case, if R, /R, = 5, ■○
An output of ±5■ appears.

In addition, when reading Vo directly without inputting it to an A/D converter (not shown), the output when no force is acting on the point of application of the force transmitting body 5 of the force sensor is 0■, so it can be read as is. use. However, when applying ■0 manually to the A/D converter, the signal level needs to be on the positive side, so in this case, as shown in FIG. It is sufficient to provide a means for applying the voltage.

Furthermore, as shown in FIG. 4, if the output impedance of the bridge circuit 11 is sufficiently low < (100Ω or less) and there is no need for impedance conversion, the first stage amplifier 20 in FIG. Output V
a and Vb may be manually input directly to the second stage amplifier 23 serving as a temperature compensation stage.

Next, a second embodiment of the present invention will be described based on FIG. Note that the description of the same parts as in the first embodiment (see FIG. 1) will be omitted, and the same parts will be denoted by the same reference numerals. The output side of the reference power generation circuit 27 as a resistance insulation separation means for sensitivity temperature compensation according to the present invention is connected to the positive side terminal of the amplifier 24 of the second stage amplifier 23 constituting the sensitivity temperature compensation circuit.

In this case, when the output voltage Vo becomes the most positive side with respect to the distortion that the bridge circuit 1l receives, the value becomes Vo
) Apply a negative reference voltage (-Vb) so as not to become O. Therefore, by applying a negative voltage that satisfies these conditions, the temperature compensation resistor Ra is always reverse biased with respect to the N-type Si substrate 6, thereby making it possible to accurately perform sensitivity temperature compensation. .

Next, a third embodiment of the present invention will be described based on FIGS. 6 and 7. In the N-type Si substrate 6, there is a P-well 2.
8 is formed. This P-well 28 is an N type S
It is in a state where it is reverse biased with -Vd with respect to the i-substrate 6. As a result, a sensitivity temperature compensation circuit 29 is configured as a resistance insulation separation means for sensitivity temperature compensation. Further, inside the P-well 128, a sensitivity temperature compensation resistor 10, which is an N-type diffused resistor, is formed.

In this example, the P-well 28 and the N-type Si
Since it is in a reverse biased state with respect to the substrate 6, the sensitivity temperature compensation resistor 10 is completely isolated from the N-type Si substrate 6. Also,
Since the potential of the P-well 28 is set to -Vd, if the potential of the sensitivity temperature compensation resistor 10 is on the positive side larger than -Vd, the sensitivity temperature compensation resistor 10 and P-
It is isolated from the wel 128. Therefore, the sensitivity temperature compensation resistor 10 and the N-type Si substrate 6 are isolated from each other, so that sensitivity temperature compensation can be performed accurately.

In addition, in the above-mentioned embodiment (see FIG. 6), P-wel
-Vd was used as the power supply for reverse biasing 128, but in addition to this, as shown in Figs. 8 and 9, another power supply -Vdw was used.
may be provided.

In the case of this embodiment, the N-type diffused resistor is used as the sensitivity temperature compensation resistor 1.
Although N-type Si has the same resistance temperature characteristics as P-type Si (the higher the temperature, the higher the resistance value), it can be used as a compensating resistor without any problems. In addition, in each of the embodiments described so far, P type,
N-type, all polarities of the voltage sources may be reversed.

Effects of the Invention The present invention provides a single-crystal structure of the sensitivity-temperature compensation resistor by setting the sensitivity-temperature compensation resistor to be electrically reverse biased with respect to the single-crystal substrate by the sensitivity-temperature compensation resistor insulation separation means. Current leakage at the boundary with the substrate can be eliminated, and as a result, temperature compensation of output sensitivity can be performed accurately over a wide range of output levels by the sensitivity temperature compensation resistor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a longitudinal sectional side view of the sensitivity temperature compensation resistance insulation and isolation means in a three-dimensional configuration, and FIG. 3 is a circuit diagram showing the first embodiment of the present invention. Circuit diagram showing the final output stage plus a reference voltage addition circuit, No. 4
The figure is a circuit diagram showing the configuration of the first stage amplifier in FIG. 1 with the structure omitted, FIG. 5 is a circuit diagram showing a second embodiment of the present invention, and FIG. 6 is a circuit diagram showing a third embodiment of the present invention. Figure 7 is a longitudinal cross-sectional side view of the circuit when it is configured three-dimensionally, Figure 8 is a circuit diagram showing another embodiment of Figure 6, and Figure 9 is a case where the circuit is configured three-dimensionally. Longitudinal side view, 1st
Figure 0(a) is a plan view showing the configuration of a conventional force sensor, Figure 10(b) is a vertical side view thereof, and Figure 11(a).
is a plan view of a single crystal substrate in another conventional example, FIG.
b) is a longitudinal sectional side view thereof, FIG. 12 is a circuit diagram showing a conventional circuit configuration when the single crystal substrate of FIG. 11(a) is used, and FIG. FIG. 2 is a circuit diagram showing an insulation breaking mechanism between 2... Action part, 3... Support part, 4... Strain body, 6
...Single crystal substrate, 8...Strain detection element, 9...Strain insensitive part, 1o...Resistance for sensitivity temperature compensation, 18, 27.29
... Resistance insulation separation means for sensitivity temperature compensation Applicant Rico Co., Ltd. 1 6 Fig. 3 7 goods 1 5 Fig. 1 Ko 〼, %'' Fig. (a) (b) 6 〇 , % , IZ〼3 Figure 3" 5

Claims (1)

[Claims] A strain-generating body is provided with one of the center and peripheral portions as a supporting portion and the other as an acting portion, and a strain detection element and a sensitivity temperature compensation resistor are provided on the surface of the strain-generating body to change electrical resistance by mechanical deformation. A force sensor having a single-crystal substrate formed thereon bonded and fixed thereto is provided with a sensitivity-temperature-compensating resistor insulating and separating means in which the sensitivity-temperature compensating resistor is electrically reverse biased with respect to the single-crystal substrate. A force sensor characterized by: