WO2013061356A1

WO2013061356A1 - Slip sensor

Info

Publication number: WO2013061356A1
Application number: PCT/JP2011/005921
Authority: WO
Inventors: 友美高橋; 潔人伊藤; 真佐圓; 長田　健一
Original assignee: 株式会社日立製作所
Priority date: 2011-10-24
Filing date: 2011-10-24
Publication date: 2013-05-02

Abstract

Provided is a highly sensitive small slip sensor, which detects slipping of an object. A slip sensor (7) has: an oscillating section (6), which has a piezoelectric film (4) and a protecting section (2) covering the piezoelectric film; and a holding section (1), which holds the oscillating section (6). The oscillating section (6) contacts an object, and detects, as slipping, signals generated due to oscillation of the oscillating section (6). The piezoelectric film (4) is disposed by being displaced from the neutral axis of the oscillating section (6) such that the piezoelectric film (4) sufficiently expands and contacts.

Description

Slip sensor

The present invention relates to a slip sensor for detecting slip of an object.

It is necessary to detect the slip when gripping an object with a robot hand. As a slip sensor, a sensor using a piezoelectric film is known. A piezoelectric film generates a signal by compression or expansion. Non-Patent Document 1 is given as a conventional slip sensor using a piezoelectric film. The slip sensor using the piezoelectric film of Non-Patent Document 1 is composed of a module integrated with silicon rubber (Non-Patent Document 1: Figure 1). A module formed of silicon rubber has a flat portion and a sensor portion, and there is a gap between the flat portion and the sensor portion. There is a piezoelectric film in the sensor unit, and a signal output when the sensor unit vibrates is detected, and it is determined as slipping.

Piezoelectric film generates a signal by applied compression and expansion, and its characteristics depend on the area. Since the slip sensor using the piezoelectric film of Non-Patent Document 1 has a low height and a wide structure, a generated signal amount is small and it is difficult to obtain a sufficient SN ratio. As a result, the detection accuracy may be lowered.

In addition, the sensor part and the outer peripheral part are integrally formed of silicon rubber, and the outer peripheral part is made of silicon rubber, so that the outer peripheral part also vibrates together with the sensor part. Such vibration dispersion also causes a decrease in detection accuracy. Furthermore, the sensor unit has a structure in which the piezoelectric film is erected on its neutral axis. However, when the sensor part bends due to vibration, there is little expansion or compression on the neutral axis, so the amount of signal generated is small.

A slip sensor that detects slipping of an object, and includes a vibration part that contacts the object and has a piezoelectric film and a protective part that covers the piezoelectric film, and a holding part that holds the vibration part. The film is arranged at a position shifted from its neutral axis.

Realize a high-sensitivity and small-sized slip sensor that detects object slip.

It is a perspective view of a slip sensor. It is sectional drawing in the A-A 'position of a slip sensor. It is sectional drawing in the B-B 'position of a slip sensor. It is a top view of a slip sensor. It is a bottom view of a slip sensor. It is a figure which shows the operation state of a slip sensor. It is a figure which shows the example which has arrange | positioned the piezoelectric film to the both ends of a neutral axis. It is a figure of an output signal when a vibration part vibrates. A manipulator provided with a slip sensor. FIG. 10A is a flowchart for gripping an object, and FIG. 10B is a flowchart for gripping an object including a reset operation.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and the common description will not be repeated.

FIG. 1 is a schematic perspective view showing a schematic configuration of a slip sensor 7 according to the present invention. 2 is a cross-sectional view of the slip sensor 7 at the A-A ′ position, and FIG. 3 is a cross-sectional view of the slip sensor 7 at the B-B ′ position.

The slip sensor 7 includes a holding unit 1 and a vibrating unit 6. The holding unit 1 is formed of a hard resin and includes a base portion that supports the vibrating unit 6 and a portion that surrounds the vibrating unit 6. The vibration unit 6 has a configuration in which the film sensor 14 is covered with the protection unit 2. The film sensor 14 includes the piezoelectric film 4 and electrodes. The piezoelectric film 4 is an element that converts strain generated in the film by an applied force into an electric signal. For example, a vinylidene fluoride resin (PVDF) film can be applied. The protection unit 2 is made of, for example, silicon rubber, and more preferably made of silicon rubber having a hardness of about 40. The electrode 5 is connected to the piezoelectric film 4 and has positive and negative terminals. For example, the positive electrode 5 a is connected to the surface of the piezoelectric film 4, and the negative electrode 5 b is connected to the back surface of the piezoelectric film 4. Since a potential difference between both surfaces of the piezoelectric film 4 caused by the distortion of the piezoelectric film 4 is generated in the electrodes, the strain of the piezoelectric film 4 can be detected by detecting this potential difference. The vibration part 6 has an array of projections 3 so that when an object slides on the upper part, the vibration part 6 is likely to vibrate by increasing friction. The size of the protruding portion 3 is configured by a height, width, and interval that are about one-tenth of the vibrating portion 6. The protrusion 3 is disposed only on the upper surface of the vibration unit 6 that contacts the object.

Thus, the aspect ratio is increased by making the height H of the vibration part 6 having the piezoelectric film 4 larger than the width W. The width W of the vibration part 6 is narrowed to reduce the size of the slip sensor, and the height H of the vibration part 6 is increased to increase the vibration and increase the sensitivity.

In addition, since the slip sensor is divided into the vibration part 6 made of a soft resin such as silicon rubber and the holding part 1 made of a resin harder than the vibration part 6, only the vibration part 6 vibrates. Since the holding unit 1 does not vibrate, vibration energy is not dispersed and detection accuracy can be improved.

In the center of the base part of the holding part 1, there is a slit 9 through which the piezoelectric film 4 passes. By passing the piezoelectric film 4 through the slit 9 and solidifying with the adhesive 30, the film sensor 14 and the vibration part 6 are fixed vertically to the holding part 1. By fixing the piezoelectric film 4 with the adhesive 30, it is possible to detect vibration with high accuracy even if wobbling occurs in a direction different from the vibration direction of the vibration unit 6. Furthermore, since the vibration of the piezoelectric film portion of the vibrating portion 6 is not easily transmitted to the piezoelectric film portion to which the electrode 5 is connected, the possibility that the connection between the piezoelectric film 4 and the electrode 5 is deteriorated due to the vibration can be reduced. In addition, as shown in FIG. 3, the piezoelectric film 4 is bent at the cavity 8 provided in the holding portion 1 and passed through the slit 9. As a result, the size of the slip sensor 7 can be reduced, and vibrations can be hardly transmitted to the piezoelectric film portion to which the electrode 5 is connected. The electrode 5 is connected to an external signal processing circuit through the wiring 19. Note that fixing the piezoelectric film 4 with the adhesive 30 is effective for preventing wobbling in a small slip sensor, but a relatively thick thickness can be provided in the base portion of the holding portion 1 in which the slit 9 is provided. In some cases, it is possible to fix the piezoelectric film 4 while suppressing wobble without using an adhesive.

Fig. 4 shows a plan view (top view) of the slip sensor. By attaching the vibrating part 6 to the center of the central depression of the holding part 1, the holding part 1 surrounds and is fixed around the vibrating part 6 with a certain interval. If the distance L between the holding unit 1 and the vibrating unit 6 (the interval in the vibration direction of the vibrating unit 6) is too small, the vibration of the vibrating unit 6 is disturbed, and if too large, the size of the slip sensor 7 is affected. When the height of the portion 6 is about 5 mm, a small interval of about 5 mm is desirable. Further, the relationship between the height of the vibrating part 6 and the holding part 1 is such that the upper end of the vibrating part 6 (projection part 3) and the upper end of the holding part 1 are positioned at the same height. A slipping object can be detected by the sliding object coming into contact with the protrusion 3 and the vibration part 6 vibrating. If the upper end of the vibration unit 6 is higher than the upper end of the holding unit 1, the vibration unit 6 does not vibrate by sticking to a sliding object and bending. Moreover, if the upper end of the vibration part 6 is too low compared with the upper end of the holding part 1, it cannot contact the sliding object.

FIG. 5 is a bottom view of the slip sensor 7. The piezoelectric film 4 is mounted on the back of the holding unit 1 in order to reduce the mounting area and reduce the size of the slip sensor 7. The base portion of the holding portion 1 has a hollow portion 8 for folding the piezoelectric film 4, a slit 9 for passing the piezoelectric film 4, and guides 10 a and 10 b for passing the wiring 19 connected to the electrode 5. The piezoelectric film 4 is fixed by being inserted into the slit 9 (when the base part of the holding part 1 is thick) or by an adhesive (when the base part of the holding part 1 is thin). On the bottom surface of the holding unit 1, the piezoelectric film 4 is passed from the surface of the holding unit 1 through the slit 9 through the slit 9, the piezoelectric film 4 is folded and mounted in the cavity 8 where the electrodes are folded, and then the wiring is passed through the

guides

10 a and 10 b. Thus, the slip sensor 7 is miniaturized with a small mounting area. Further, the vibration is hardly transmitted to the piezoelectric film portion to which the electrode 5 is connected.

FIG. 6 is a diagram showing an operating state of the slip sensor 7. The initial state of the vibration part 6 is as shown in FIG. 3, but the tip of the vibration part 6 (projection part 3) sticks to the object 11 in the sliding direction 20 of the object 11 according to the slip of the object 11. Thus, the object 11 is distorted in the sliding direction. This is the state of FIG. Furthermore, when the force for returning the vibration part 6 becomes larger than the slipping force, that is, the shearing force applied to the vibration part 6, the vibration part 6 returns to the direction for restoring the distortion. As described above, the vibration unit 6 is displaced to the left and right according to the slip of the object 11, that is, the vibration unit 6 vibrates, so that the piezoelectric film 4 in the vibration unit 6 also vibrates, and the output signal changes during the slip period. To do. Thus, the slip sensor 7 of the present invention captures slip as vibration. The vibration part 6 has the protrusion 3 on the upper surface thereof, and thus vibrates regardless of the shape of the surface of the sliding object 11.

The piezoelectric film 4 is applied with force by vibration, and the piezoelectric film 4 expands and compresses to change the output signal. At the neutral axis of the vibration part 6, since the expansion and compression of the vibration part 6 is small compared to the side surface of the vibration part 6, the amount of signal change generated by the piezoelectric film 4 is small. As shown in FIG. 3, the film sensor 14 (piezoelectric film 4) is shifted from the neutral shaft 31 of the vibration unit 6 and is disposed closer to the side surface, so that the piezoelectric film 4 is sufficiently expanded and compressed, and a large signal is obtained. A quantity is obtained. Since the protection part 2 of the vibration part 6 has the purpose of protecting the piezoelectric film 4, it is desirable that the film sensor 14 be disposed as close to the side surface of the vibration part 6 as possible so as not to be exposed.

FIG. 7 shows a modified example in which two

piezoelectric films

4 a and 4 b are placed on both sides of the vibration part 6 in order to obtain a large signal amount. When the piezoelectric film 4a is compressed by deformation of the vibration part 6 due to slipping of the object, the piezoelectric film 4b expands and contracts. As described above, since signals having opposite polarities are obtained by the piezoelectric film 4a and the piezoelectric film 4b, a large signal amount can be obtained by taking the difference.

FIG. 8 shows an output signal of the potential difference of the electrode 5 when the vibrating part 6 of FIG. 3 vibrates. In the sliding state, large positive and negative peaks are repeated according to the vibration, and small noise is output in the non-sliding state. The piezoelectric film 4 repeats positive and negative peaks according to the vibration by the change of the voltage generated by the vibration while sliding. Since the amount of signal increases when slipping, it is suitable to perform threshold processing and hold processing for slip detection. When the obtained output signal is larger than the positive threshold or smaller than the negative threshold, 1 is set. Otherwise, 0 is assumed. A peak is seen in the waveform, that is, the period in which peaks and valleys are repeated is slipping, but if only threshold processing is used, only one peak is captured. In order to continuously consider the period in which the peak is present as the slip, the threshold processing result is subjected to hold processing for the same length of time as the positive / negative peak cycle in which the output signal repeats. Similarly, when the obtained output signal is larger than the positive threshold or smaller than the negative threshold, it is set to 1. Otherwise, 0 is assumed. In this way, the threshold processing and the hold processing are repeated, and it is assumed that slipping occurs when 1 is output and slipping does not occur while 0 is output.

In addition, the vibration part 6 vibrates at the natural frequency of the protection part 2 in a sliding state and is different from the noise frequency. This is because the piezoelectric film 4 is a very soft material, so that the natural frequency of the vibration part 6 is substantially the natural frequency of the protection part 2. Therefore, it is also possible to detect the slip state by signal processing that extracts the natural frequency of the protection unit 2 in detecting the slip. The period during which the natural frequency of the protection unit 2 can be extracted is regarded as slipping. Methods for extracting frequencies include Fourier transform and wavelet transform.

FIG. 9 shows a manipulator 13 that grips an object by detecting slippage. The manipulator includes a grip portion 12 and a vibration portion 6. The grip portion 12 has a hole 35, and the manipulator can be downsized by attaching the vibrating portion 6 to the hole 35. Although details are not shown, as in FIG. 3 or FIG. 7, there is a slit large enough to insert the piezoelectric film in the center of the hole 35, and the piezoelectric film is fixed. If the distance between the gripping part 12 and the vibration part 6 is too small, the vibration of the vibration part 6 is hindered. If it is too large, the manipulator 13 is downsized. Pressure sensors can be arranged on the surface of the grip portion 12. It is also possible to grip an object by combining slip and pressure detection.

FIG. 10 is a flowchart when the robot hand grips an object using the manipulator 13. In the case of FIG. 10 (a), the manipulator 13 pinches an object (S1), lifts (S2), lifts with the same force if no slip is detected by the slip sensor (S3), and pinches strongly if slip is detected. (S4) The presence / absence of slip is determined again. In the case of FIG. 10B, a reset operation is performed. The manipulator 13 pinches the object (S11), lifts (S12), and determines slipping. If no slip is detected, the manipulator 13 lifts with the same force (S13). If slipping is detected, the manipulator 13 resets the object. Perform (S14), and then pinch firmly (S15), lift (S12), and once again determine whether there is any slip.

DESCRIPTION OF SYMBOLS 1: Holding part, 2: Protection part, 3: Projection part, 4: Piezoelectric film, 5: Electrode, 6: Vibration part, 7: Slip sensor, 8: Cavity part which folds electrode 5, 9: Slit which lets electrode 5 pass 10: guide, 11: heel object, 12: heel gripping part, 13: manipulator, 14: film sensor.

Claims

A slip sensor for detecting slipping of an object,
A vibrating portion that contacts the object and has a piezoelectric film and a protective portion that covers the piezoelectric film;
A holding part for holding the vibrating part,
In the vibration unit, the piezoelectric film is disposed at a position shifted from the neutral axis.
In claim 1,
The holding part has a slit,
A slip sensor in which the piezoelectric film is fixed to the holding portion by inserting an adhesive in the slit or by inserting the piezoelectric film into the slit.
In claim 2,
The slip sensor, wherein the piezoelectric film is bent between a slit of the holding portion and a portion where an electrode is connected to the piezoelectric film.
In claim 3,
A slip sensor in which the height of the vibration part is larger than the width.
In claim 4,
The holding part has a base part and a surrounding part surrounding the base part,
The slit is formed in the base part,
A slip sensor in which a tip of the vibration part and a tip of the surrounding part are located at the same height.
In claim 5,
The holding part is a slip sensor harder than the vibrating part.
In claim 1,
Having two piezoelectric films,
The slip sensor which arrange | positions the said 2 piezoelectric film on the both sides shifted from the neutral axis of the said vibration part.
In claim 1,
The slip sensor which has a projection part on the upper surface of the said vibration part.