JPH07198459A - Load detector - Google Patents

Abstract

PURPOSE:To monitor condition concerning fatigue failure by providing a construction to obtain information pertaining to a dynamic load. CONSTITUTION:This apparatus contains a mechanical structure part sensitive to a load and a first load detecting element 1 to detect a load working on the mechanical structure part. Moreover, a signal processing means 3 is added to process an output signal of the load detecting element and a second load detecting element 2 is provided to detect a distortion possibly leading to fatigue failure of an elastic body. The load detecting element detects an intrinsic load and the second load detecting element detects a dynamic load working on the elastic body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load detector, and more particularly to a load detector which detects a force or a moment acting on various objects or both and is used as a force sensor in an industrial robot.

[0002]

2. Description of the Related Art Conventional load detectors include, for example, various beam type load detectors or parallel plate type load detectors. Most of these load detectors are configured to detect the degree of deformation of an elastic body provided inside the load detector and obtain the load acting on the load detector based on the detected value. Has been done. As a means for detecting the deformation of the elastic body, a strain gauge is generally used, but a new one uses a photosensor or a photo-sensitive semiconductor. In a detection device using a strain gauge, a plurality of strain gauges are dispersedly arranged at appropriate places in an elastic body, and a Wheatstone bridge circuit is formed by a plurality of strain gauges in an electric circuit, so that a load is applied to the elastic body to prevent deformation. When it occurs, the resistance value of each strain gauge changes, the equilibrium state of the Wheatstone bridge circuit is broken, and an output voltage proportional to the load is generated at the output end of the Wheatstone bridge circuit. The output signal of the Wheatstone bridge circuit becomes the output signal of the load detector.

As shown in FIG. 5, an output signal of a load detector 52 including four strain gauges connected as a Wheatstone bridge circuit 51 is processed by a signal processing means 53. The signal processing means 53 includes a reference voltage unit 54, an amplifier 55 that amplifies the output signal of the load detector 52 to a predetermined level, a low-pass filter 56 that removes high frequency components as noise, an A / D converter 57, and the obtained digital signal. It includes an arithmetic processing unit 58 for performing a predetermined arithmetic operation on the load data of the value and storing it, and an I / O interface 59.
The arithmetic processing means 58 sends load data to an external host device through the I / O interface 59 as needed.

[0004]

The load detector described above is used as a force sensor for force control in a robot such as a grinding robot which operates under force control. In such a use, the load detector is attached to the hand of the robot body, and the hand effector is attached to the end of the load detector. A typical example of the hand effector is a rotary tool such as a grinder that repeatedly generates vibration. The load applied to the rotary tool is detected by the load detector, and the load information detected by the load detector is sent to the control means and used for control relating to the grinding work by the rotary tool.

In the above-mentioned usage of the load detector, when the rotary tool attached to the tip of the load detector rotates, the center of gravity of the rotary tool swings, so that a dynamic load is repeatedly generated. The elastic body provided in the load detector is deformed in response to this dynamic load. This dynamic load is an important factor that leads to fatigue failure for elastic bodies,
It is important to detect the effect of dynamic load on the elastic body.

However, in the processing of the output signal from the conventional load detector, as described above, the low-pass filter 56 is provided for the purpose of accurately detecting the load related to the force work. Since the cut-off frequency of this low-pass filter is set lower than the rotational speed of the rotary tool, the signal related to the dynamic load is removed from the output signal of the load detector. Then, the data regarding the dynamic load cannot be obtained from the load data generated by the signal processing means 53. As described above, if the load detector is not aware of the dynamic load and is used for a long period of time, the load detector is destroyed when the stress generated in the elastic body exceeds the fatigue strength of the elastic body. Therefore, it is extremely important to measure the influence of the dynamic load or the history of the dynamic load. However, with the structure of the sensor unit and the circuit configuration of the processing means of the detection signal in the conventional load detector, it is not possible to obtain information on the dynamic load.

It is an object of the present invention to provide a load detector which is provided with a structure for obtaining information on dynamic load and is capable of monitoring a situation concerning fatigue fracture.

[0008]

SUMMARY OF THE INVENTION A load detector according to the present invention is a mechanical structure that deforms in response to a load to generate stress, and a mechanical structure that detects the deformation of the mechanical structure. A first load detecting element composed of a plurality of strain gauges for detecting a load acting on the section, on which signal processing means for processing an output signal of the load detecting element is added, Further, a second load detecting element is provided for detecting a strain that causes fatigue failure of the elastic body. The first load detection element detects an original load that is a measurement target, and the second load detection element has a function of detecting the dynamic load acting on the elastic body. The data of the dynamic load detected by the second load detection element is managed by the signal processing means. The signal processing means calculates and processes the output signal of the second load detection element to obtain data on the fatigue fracture. Each of the first and second load detecting elements is configured as a Wheatstone bridge circuit using a strain gauge.

The load signal detected by the first load detecting element is processed by the signal processing means after being input through the low pass filter. The signal related to the dynamic load detected by the second load detection element is directly input and processed without passing through the low pass filter when the same signal processing means as described above is used for signal processing. It is also possible to provide a dedicated signal processing means for processing the output signal of the second load detecting element. Also in this case, the high frequency removal processing is not performed, and the output signal is processed as it is.

The load detecting element for detecting the strain leading to fatigue failure is preferably attached to a portion (stress concentrating portion) of the elastic body where the maximum strain occurs, so as to measure the number of times the maximum strain occurs. Composed. In this case, the load detecting element used to measure the number of times strain has occurred is provided separately from the load detecting element for detecting the load.

Further, the load detecting element for detecting the load can be used together as the load detecting element for detecting the strain leading to fatigue failure.

[0012]

The load detector detects the load acting on the elastic body by detecting the deformation of the elastic body. When the elastic body is deformed, stress is generated in this deformed portion, and a portion where the stress is concentrated is formed. The location where the stress concentration portion is formed is determined depending on the shape of the elastic body. For elastic bodies,
A first load detecting element for detecting a load that is an original measurement target and a second load detecting element for detecting a dynamic load and measuring the number of occurrences thereof are provided. The second load detecting element is preferably attached to the stress concentrating portion.

For example, when the load detector is used as a force sensor for a grinding robot, a rotary tool is attached to the tip of the load detector provided at the tip of the robot body. The load detector detects the load caused by the work applied to the rotary tool by the first load detection element, and at the same time, detects the dynamic load generated by the rotation operation of the rotary tool by the second load detection element. The signal output from the second load detection element is directly A / D converted without passing through the low pass filter and stored in the memory of the signal processing means. The dynamic load thus generated is detected by the second load detection element of the load detector, and various data regarding the dynamic load and data such as the number of times the dynamic load is generated are stored in the memory of the signal processing means. The determination means of the signal processing means uses the obtained peak value of the dynamic load and the number of occurrences within a fixed time as the S of the load detector prepared in advance.
By comparing with the -N curve, the possibility of fatigue failure is determined, and the determination result is output to an external higher-level device if necessary. The SN curve is obtained experimentally for each material forming the load detector, and is a characteristic curve showing the correlation between the load stress and the number of repetitions until the material breaks.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

A first embodiment will be described with reference to FIGS. FIG. 1 shows a main part of a load detector according to the present invention. In FIG. 1, 1 is a first load detecting element for detecting a load which is an original measurement object, and 2 is a motion which is repeatedly generated. The second load detection element for detecting the dynamic load, and 3 is a signal processing means. The load detector itself is composed of a mechanical structure portion including an elastic body and a sensor portion including load detection elements 1 and 2 attached to the elastic body. Usually, these two portions are assembled to detect a load. The vessel is formed as a single unit. In the illustrated example, the broken-line block 4 conceptually represents the load detector, and the mechanical structure portion including the elastic body is not shown. The mechanical structure part is arbitrary. The above-mentioned dynamic load is a load that causes a strain that causes fatigue fracture of the mechanical structure portion, and the load detection element 2 is provided for the purpose of obtaining data on the above-mentioned dynamic load by detecting the strain. It is a thing.
The signal processing means 3 has a structure added to the load detector 4.

The load detecting element 1 and the load detecting element 2 are structurally the same and are preferably configured to connect four strain gauges to form a Wheatstone bridge circuit. Generally, four strain gauges are attached to predetermined portions of the structural portion of each load detection element. Four
One strain gauge is represented by a resistance as an electric circuit element. The strain gauge has a resistance value corresponding to the stress generated at the attachment point. Depending on the resistance of the strain gauge, the Wheatstone bridge circuit produces a voltage output corresponding to stress. The load detecting element 1 is not generally single, and for example, in a 6-axis force sensor, six load detecting elements 1 are provided at predetermined positions of an elastic body. Therefore, the signal system of the load detecting element 1 is 6 channels in this case. Generally, the load detection element 1 is provided with an n-channel (n ch) signal system according to the performance of the load detector. The load detecting element 2 provided for detecting a dynamic load is also formed by four strain gauges g1, g2, g3, g4. In this case, one strain gauge g1
It is provided at the stress concentration portion in the structure of the load detector 2.
The stress concentration part is a part where the maximum strain occurs. The other three strain gauges g2 to g4 are for forming a Wheatstone bridge circuit. The three strain gauges g2 to g4 may be dummy gauges, or, when there are a plurality of stress concentration portions, may be attached to each stress concentration portion.

The signal processing means 3 has, for example, a reference voltage section 31 of, for example, 4 volts, amplifiers (AMP) 32A and 32B for amplifying the output signals of the respective load detecting elements, a low pass filter 33, and an A / D converter. 34, a microprocessor unit (MPU) 35 for calculating and processing data, a memory 36, and an I / O interface 37. The amplifier 32A and the low-pass filter 33 are the load detection element 1
N channels are provided corresponding to. Reference voltage unit 31
Is for applying a required voltage to the input ends of the Wheatstone bridge circuits of the load detecting elements 1 and 2. In this case, when no load is detected by each of the load detecting elements 1 and 2, each Wheatstone bridge circuit is held in a balanced state and a predetermined voltage is output. Load detector 4
When a load is applied to the elastic body, the elastic body is distorted, and a voltage proportional to the load is generated from the output terminals of the load detection elements 1 and 2.
The output signal from the load detection element 1 is amplified by the amplifier 32A, the high-frequency component is removed by the low-pass filter 33, and converted into a digital value by the A / D converter 34. The output signal from the load detecting element 2 is amplified by the amplifier 32B and then directly input to the A / D converter 34 without passing through the low-pass filter 33, where it is converted into a digital value. The digitized output of each load detection element is input to the MPU 35 as load data and further stored in the memory 36.

In the above description, since the load detecting elements 1 and 2 provided inside the same load detector 4 detect the load applied to the load detector 4, basically, according to the common load. Output a detection signal. The difference is that the load detection element 2 for detecting the dynamic load is provided in the stress concentration portion of the mechanical structure portion, so that the amplitude of the detection signal becomes large.

Here, FIG. 2 shows the waveforms of the output signal a of the amplifier 32A, the output signal b of the low-pass filter 33, and the output signal c of the amplifier 32B in the signal processing means 3.
The output signals a and c are frequency signals, and the output signal c is the output signal a.
It can be seen that the amplitude is larger than. The output signal c of the amplifier 32B is a signal generated due to a dynamic load. Further, in the output signal b of the low-pass filter 33, high frequency components are removed and converted into direct current. The obtained DC voltage value is the force data applied to the rotary tool in the case of a grinding robot that performs manual work, for example. The signal b and the signal c are converted into digital values by the A / D converter 34. The A / D converter 34 needs a sampling frequency that is, for example, 10 times the frequency of the repeated dynamic load, that is, the frequency of the signal c.

In the MPU 35, regarding the data regarding the dynamic load, for example, the peak value | P1 of the signal c shown in FIG.
|, | P2 | (> 0) is used to obtain the average value. Also, the number of times the peak value occurs during a certain fixed time is counted. The data thus obtained is stored in the memory 36. Further, the signal processing unit 3 is input with the SN curve of the material forming the elastic body of the load detector 4 as shown in FIG. 3 in advance and stored in the memory 36.
The obtained average value and the number of times of peak value generation are compared with the prepared SN curve. Based on this comparison, it is determined whether or not the generated dynamic load has a high possibility of causing fatigue failure, or if fatigue failure occurs, what time it takes, etc. The obtained determination result is sent to the external host device via the I / O interface 37. The upper device notifies the determination result through various output devices.

The above-described fatigue fracture determination processing can be configured to be performed when the fatigue breakdown determination instruction 41 is given from the host device to the signal processing means 3, and the processing of the MPU 35 of the signal processing means 3 can be performed. If the speed allows, the fatigue fracture determination process may be always performed, and the dynamic load generation state, that is, the fatigue fracture state may be constantly monitored. Further, in the above embodiment, the signal processing means 3 for the load detecting element 1 is used as the signal processing means for obtaining the data regarding the dynamic load. However, the signal processing means dedicated to the load detecting element 2 is provided. You can also do it.

In the above embodiment, in addition to the load detecting element 1, the load detecting element 2 for detecting the strain caused by the dynamic load which may lead to fatigue fracture is used as the load detector 4.
Set up in. The load detection element 2 is preferably attached to a position where the maximum strain of the elastic body occurs, but is not limited to this. In the case of the configuration of the above-described embodiment, since the dedicated load detecting element 2 is attached at the optimum position of the elastic body, the data regarding the dynamic load can be accurately extracted. In particular, when it is attached to a place where maximum strain occurs, highly accurate detection can be performed.

FIG. 4 shows another embodiment. In FIG. 4, the same elements as those described in the above embodiment are designated by the same reference numerals. In this embodiment, the output signal of any one channel of the original plurality of load detecting elements 1 provided to detect the load of the measurement object is separately taken out and is output through the A / It is configured to perform D conversion and use the signal of this channel for monitoring the dynamic load. Therefore, the load detection element 2 described in the above embodiment need not be specially provided. That is, the load detecting element 2 is attached to the stress concentrating portion of the elastic body, the maximum strain generated in the stress concentrating portion is not directly detected, and the stress concentration is determined based on the signal relating to the dynamic load detected by the above detection structure. It is configured to estimate the distortion occurring in the part. Therefore, the MPU 35 of the signal processing means 3 is provided with a function for estimating. In this embodiment, the detection accuracy is slightly lowered, but the structure of the load detector can be simplified and the load detector can be manufactured at low cost.

The circuit configuration of the signal processing means 3 may be independently configured as in the above embodiment, or may be incorporated in the controller of the force controller.

[0025]

As is apparent from the above description, according to the present invention, since the load detector is provided with the structure for detecting the strain leading to fatigue failure, it is attached to, for example, the hand portion of the force control robot, and further ahead. In a load detector with a rotating tool attached to it, it is possible to detect the strain caused by the dynamic load generated by the rotation of the rotating tool, that is, the strain that leads to fatigue fracture, and the data related to the dynamic load, such as peak value and the number of occurrence And the life of the load detector can be determined. This allows the user to prevent fatigue failure of the load detector in advance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a load detector according to the present invention.

FIG. 2 is a waveform diagram showing a signal waveform of each part of the circuit.

FIG. 3 is a diagram showing an example of an SN curve.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional load detector.

[Explanation of symbols]

1 load detector 2 load detector for detecting a dynamic load 3 signal processing means 4 load detector 33 low-pass filter

Claims (4)

[Claims] 1. A mechanical structure part, and a load detection element for detecting deformation of the mechanical structure part to detect a load acting on the mechanical structure part. In a load detector to which a processing means for processing an output signal is added, a load detecting element for detecting a strain that leads to fatigue failure of the mechanical structure portion, and the fatigue failure based on an output signal of the load detecting element A load detector, which is provided with a processing means for calculating and processing data regarding the load. 2. The load detector according to claim 1, wherein the load detecting element for detecting the strain that leads to the fatigue fracture is attached to a portion of the mechanical structure where maximum strain occurs, A load detector, which is used to measure the number of strain occurrences. 3. The load detector according to claim 1, wherein the load detection element for detecting the load is used as the load detection element for detecting a strain leading to the fatigue fracture. Load detector 4. The load detector according to claim 1, wherein an output signal from the load detection element for detecting the load is signal processed after passing through a low pass filter, A load detector characterized in that an output signal from the load detecting element for detecting a strain leading to the fatigue failure is directly processed without passing through a low pass filter.