JPH0843220A - Circuit for automatically correcting zero point of inner force sensor - Google Patents

Abstract

PURPOSE:To provide a circuit for automatically correcting zero point of inner force sensor which can maintain the measurement accuracy of an inner force sensor at a high level by automatically correcting the zero point of the sensor at the time of measuring torque with the sensor. CONSTITUTION:A control circuit 6 samples voltage information obtained from an inner force sensor 3 and calculates the deviation of the present zero point of the sensor 3 from the mean value of the sampled values. Then the circuit 6 discriminates the no-load state of the sensor 3 by comparing the calculated deviation with a prescribed threshold and updates the zero point by setting the mean value, at which the no-load state is discriminated, as a new zero point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a force sensor attached to the tip of a hand of a manipulator or the like to detect force or torque, and particularly when converting voltage information obtained from the force sensor into force information. , A circuit for automatically correcting the zero point.

[0002]

2. Description of the Related Art Conventionally, a manipulator as shown in FIG.
A force sensor (3) composed of a strain gauge or a piezoelectric sensor is attached to the object gripping end of the hand mechanism (2) of (1) to detect the force or torque acting on the target object, and to detect the detected value. Feedback is performed on the control of the manipulator (1). As a result, a reliable gripping operation is realized even for a flexible target object. As the manipulator (1), for example, a 6-axis vertical articulated robot is adopted.

The output of the force sensor (3) is temperature-compensated,
After signal processing such as filtering and amplification is performed, the signal is supplied to the control circuit of the manipulator (1).

By the way, when the force or torque is detected by the force sensor (3), the output of the force sensor (3) is taken out as a voltage. Therefore, as shown in FIG.
The relation with (or torque) F is made into a function in advance, and the force F is calculated using this predetermined function F = f (V).
Here, the voltage V is a value obtained by subtracting the output voltage Vo in the unloaded state in which no force is applied to the force sensor (3) from the output voltage Vp in a state where the force is applied to the force sensor (3) ( V
p-Vo).

[0005]

However, the function F = f (V) shown in FIG. 5 is, for example, the influence of temperature and the hysteresis component which the force sensor itself or the signal processing circuit has as its characteristic. Due to the influence, it shifts up and down as shown by the broken line in the figure. Conventionally, this is dealt with by periodically performing zero correction, but there is a problem that it is necessary to perform zero correction frequently in order to maintain high accuracy, which is extremely complicated.

An object of the present invention is to provide a zero-point automatic correction circuit for a force sensor which can automatically perform zero-point correction and maintain high measurement accuracy.

[0007]

A zero-point automatic correction circuit for a force sensor according to the present invention comprises a sampling means for sampling voltage information obtained from the force sensor, an average value of sampling values of the voltage information, and a current zero point. Deviation calculating means for calculating the deviation, a comparison judging means for judging the no-load by comparing the calculated deviation with a predetermined threshold, and a zero-point updating means for setting the average value judged as no-load to a new zero point. It is equipped with

Another zero-point automatic correction circuit according to the present invention comprises sampling means for sampling voltage information,
A first deviation calculating means for calculating a deviation between the sampling value of the voltage information and the current zero point; a first comparing and judging means for comparing the calculated deviation with a first threshold value to judge no load; The judgment means for judging whether or not the no-load judgment by the comparison judgment means is continuously performed for a predetermined plurality of times, and the average value of the sampling values for the no-load for a plurality of times judged by the judgment means. And an average value calculation means for calculating the deviation, a second deviation calculation means for calculating a deviation between the calculated average value and the current zero point, and the calculated deviation with a second threshold value to determine the authenticity of no load. The second comparison / determination means and the zero point updating means for setting the average value determined to be authentic as a new zero point.

[0009]

In the first automatic zero correction circuit, the zero correction is performed in the process of actually attaching the force sensor to the machine to be measured and measuring the force or torque. That is, the voltage information is sampled from the force sensor, and the average value of the sampled values is calculated over a plurality of predetermined times. Then, the deviation between the average value and the current zero point is compared with a predetermined threshold value, and it is determined whether or not the period when the average value is obtained is no load.

Generally, in the measurement of force by a force sensor, after a force is applied for a certain period of time, the load is not applied due to the rest of the measuring object machine, and then the force is applied. Is repeated. In this process, in a load state in which force is acting on the force sensor, the deviation between the average value of the sampling values and the zero point becomes a large value to some extent and exceeds the predetermined threshold value. On the other hand, in a no-load state in which no force acts on the force sensor, the deviation between the average value of the sampling values and the zero point becomes zero or a small value, which is below the predetermined threshold value.

The above deviation is caused by the displacement of the zero point of the force sensor. Therefore, the average value determined as no load is set as a new zero point, and the zero point is updated.

In the second automatic zero-correction circuit, first, the first comparison / determination means determines the no-load based on a relatively gentle criterion (first threshold value) considered to be no-load. To do. As a result, a large amount of data is collected as a no-load determination target. Further, depending on whether or not this no-load determination is continuously performed for a predetermined number of times, it is confirmed that the no-load state is not instantaneous and has a certain degree of continuity. Then, the average value of the sampling values for no load over a plurality of times is calculated, and the deviation between the calculated average value and the current zero point is calculated,
The no-load is determined by comparing the deviation with the second threshold value. Here, the second threshold value is set smaller than the first threshold value, and the truly unloaded state is selected from the unloaded state determined by the first threshold value.

Since the above-mentioned deviation occurs due to the displacement of the zero point of the force sensor, the average value determined to be truly unloaded is set as a new zero point, and the zero point is updated. Of.

[0014]

According to the zero-point automatic correction circuit of the force sensor of the present invention, when the zero point is deviated, the zero point is automatically detected and the zero point is corrected. Is unnecessary, and high measurement accuracy is always maintained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A manipulator according to the present invention shown in FIG.
An example implemented in (1) will be described in detail with reference to the drawings. FIG. 2 shows a control system of the manipulator (1). The hand mechanism (2) of the manipulator (1) is attached with a force sensor (3) including a strain gauge or a piezoelectric sensor. .

The output signal of the force sensor (3) is sent to a signal processing circuit (4) and subjected to necessary signal processing such as temperature compensation, noise removal by a filter and amplification, and then an A / D converter.
After (5), a control circuit consisting of a microcomputer
It is supplied to (6). The control circuit (6) includes a force sensor (3)
Based on the force information detected by the hand mechanism (2)
A force control program (7) for controlling the operation of (1) and a program (8) for automatically correcting the zero point of the force sensor (3) are registered as described later.

FIG. 3 shows a processing procedure by the zero point automatic correction program (8).
(8) is repeated at a fixed sampling cycle (for example, 50 ms). The control circuit (6) is provided with a memory for storing the zero point of the force sensor (3), and an appropriate initial value is written in advance.

First, in step S1, the output voltage Vp of the force sensor (3) is taken in, and in step S2, the absolute value of the value obtained by subtracting the output voltage Vp from the current zero point Vo and a predetermined first value. The magnitude is compared with the threshold value A (for example, 10 mV). When the absolute value of the difference is larger than the first threshold A, step S3
, The current zero point Vo is subtracted from the output voltage Vp to calculate the voltage value V, and the function F =
The force F is calculated using f (V).

On the other hand, in step S2, when the absolute value of the difference is smaller than the first threshold value A, the process proceeds to step S4, and YES is determined in step S2 a predetermined number of times.
(For example, 5 times) It is judged whether or not it is repeated continuously. Here, if the no-load is not an instantaneous one and the actual no-load is the actual no-load, the determination is YES.

If YES is determined in step S4, the process proceeds to step S5, and the average value Va of the sampling values of the output voltage Vp over a plurality of times is calculated. Then, the absolute value of a value obtained by subtracting the average value Va from the current zero point Vo and a predetermined second threshold value (for example, 5 mV) are compared in magnitude. Here, in the case of true no load, the absolute value of the difference is the second
It becomes smaller than the threshold value B, and YES is determined.

If YES is determined in step S5, the process proceeds to step S6 and the current zero point Vo is rewritten with the average value Va of the output voltage to update the zero point.

In the procedure of FIG. 3, the no-load determination is performed twice in step S2 and step S5 for the reason shown in FIG. That is, the sampling example (1) of FIG.
Then, the output voltage Vp slightly fluctuates between the first threshold value A and the second threshold value B, and does not fall below the second threshold value B. Therefore, in this example, it is considered that an extremely small force continuously acts on the force sensor (3).

On the other hand, in the sampling example (2), the zero point Vo
A large variation occurs in the output voltage Vp within the range of the first threshold value A, centering on, and the data that is below the second threshold value B is included therein. Therefore, in this example, it is considered that no continuous force acts on the force sensor (3).

When the procedure of FIG. 3 is executed for the sampling example (1), no load is determined in step S2, but NO is determined in step S5, and the zero point correction based on these data is not performed. On the other hand, in the sampling example (2), it is determined that there is no load in both step S2 and step S5, and appropriate zero point correction is performed based on these data.

In step S2, if the strict second threshold value B in step S5 is used instead of the first threshold value A, most of the data are judged to be NO in the next step S4, and the target zero point is determined. The correction may not be substantially made. Therefore, in the procedure of FIG. 3, the first threshold value A is set to a relatively large value, while the second threshold value B is set to a small value, thereby realizing zero point correction under severe conditions while targeting a large amount of data as a whole. I did.

Therefore, according to the above-mentioned zero point automatic correction circuit, the zero point can be automatically corrected with high reliability. Particularly, in the manipulator (1) as shown in FIG. 1, if there is an error in the zero correction of the force sensor (3), the target object grasped by the hand mechanism (2) may be damaged. According to the zero-point automatic correction circuit, the operation can be continued for a long time without maintenance, and the operation rate is increased.

The above description of the embodiments is for explaining the present invention and should not be construed as limiting the invention described in the claims or reducing the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of drawings]

FIG. 1 is a front view showing a manipulator in which the present invention is implemented.

FIG. 2 is a block diagram showing a manipulator control system embodying the present invention.

FIG. 3 is a flowchart showing a zero correction procedure.

FIG. 4 is a graph illustrating a variation pattern of a sampling value of an output voltage.

FIG. 5 is a graph illustrating a function for converting voltage information into force information.

[Explanation of symbols]

 (1) Manipulator (2) Hand mechanism (3) Force sensor (4) Signal processing circuit (5) A / D converter (6) Control circuit (7) Force control program (8) Zero-point automatic correction program

Claims (2)

[Claims] 1. A circuit for correcting a zero point when converting voltage information obtained from a force sensor into force information, comprising: sampling means for sampling voltage information; average value of sampling values of voltage information; Deviation calculation means for calculating the deviation of the zero point, comparison judgment means for judging the no load by comparing the calculated deviation with a predetermined threshold value, and zero point update for setting the average value judged as no load to a new zero point A zero-point automatic correction circuit for a force sensor, comprising: 2. A circuit for correcting a zero point when converting voltage information obtained from a force sensor into force information, comprising: sampling means for sampling the voltage information; deviation between the sampling value of the voltage information and the current zero point. A first deviation calculating means for calculating, a first comparison judging means for judging the no-load by comparing the calculated deviation with a first threshold value, and a predetermined no-load judgment by the first comparison judging means. A determination means for determining whether or not the measurement is continuously performed for a plurality of times, and an average value calculation means for calculating an average value of sampling values for no load determined by the determination means for a plurality of times. Second deviation calculating means for calculating the deviation between the average value and the current zero point, second comparing and judging means for comparing the calculated deviation with a second threshold value to judge the authenticity of no load, and the authenticity Flatness judged Zero automatic compensation circuit of the force sensor characterized in that it comprises a zero point update means for setting a value to a new zero point.