JP2009257573A - Linear motion expandable actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a linear motion expandable actuator on which a strain sensor is easily mounted, and which achieves an improved signal-noise ratio. <P>SOLUTION: The linear motion expandable actuator 1 includes a tube 2 which expands and contracts in the long axial direction, and the strain sensor 3 having an elastic body 4 for covering an outer circumferential surface of the tube 2 along a circumferential direction to detect expansion/contraction strain in a circumferential direction of the tube 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a linear motion expansion / contraction actuator that expands and contracts in the long axis direction.

A McKibben type actuator is known as a linear motion expansion / contraction actuator. The McKibben actuator is a typical pneumatic soft actuator and is also called a McKibben rubber artificial muscle. The McKibben-type rubber artificial muscle includes a sleeve in which fiber cords are knitted in a net shape and a rubber tube covered with the sleeve. The radial expansion force generated by increasing the internal pressure of the rubber tube is converted into the contraction force in the axial direction of the rubber tube by the fiber cord.
Such a McKibben actuator is a linear motion actuator having contractility. For this reason, a rotary sensor such as a rotary encoder cannot be used to detect distortion in the long axis direction of the McKibben actuator.
FIG. 7 is a diagram for explaining a method of measuring the strain of the linear motion expansion / contraction actuator using a linear motion potentiometer. By attaching the linear motion type potentiometer 91 in parallel with the linear motion expansion / contraction actuator 92, it is possible to detect distortion along the major axis direction of the linear motion expansion / contraction actuator 92.

  FIG. 8 is a diagram for explaining a method of measuring the strain of the linear motion extendable actuator by direct measurement in the long axis direction using a conductive rubber. As shown in FIG. 8, a sensor has been developed in which conductive rubber is attached to the side surface of an actuator, and the displacement in the major axis direction of the actuator is measured by a change in the resistance value of the conductive rubber (Non-Patent Document 1).

Further, a configuration is known in which a linear encoder is wound around an actuator to measure the circumferential displacement of the actuator (Non-patent Document 6).
JP 2000-258112 A (published on September 22, 2000) Yamamoto, Y .; Kure, K .; Iwai, T .; Kanda, T .; Suzumori, K., "Flexible displacement sensor using piezoelectric polymer for intelligent FMA," Intelligent Robots and Systems, 2007. IROS 2007. IEEE / RSJ International Conference on, vol., No., Pp.765-770, Oct. 29 2007-Nov. 2 2007 Wakimoto, Shuichi Suzumori, Koichi Kanda, Takefumi Development of Intelligent McKibben Type Actuator: 1st Report, Realization of Position Servo System with Built-in Flexible Displacement Sensor (Mechanical Systems, Measurement, Automatic Control) 03875024 The Japan Society of Mechanical Engineers 20050925 71 709 2754-2760 http://ci.nii.ac.jp/naid/110006264860/ Jun Ueda, Masayuki Matsugashita, Reishi Oya, and Tsukasa Ogasawara, "Control of Muscle Force During Exercise Using a Musculoskeletal-Exoskeletal Integrated Human Model," Experimental Robotics, The 10th International Symposium on Experimental Robotics, Springer Tracts in Advanced Robotics, ISBN: 978 -3-540-77456-3, pp. 143--152, Volume 39, 2008 Ming Ding, Jun Ueda, Tsukasa Ogasawara, "Development of MAS-a system for pin-pointed muscle force control using a power-assisting device", Proceddings of the 2007 IEEE International Conference on Robotics and Biomimetics (Robio2007), December 15-18 , Sanya, China, 2007 Daisuke Nakamura, Atsushi Ueda, Tsukasa Ogasawara: "Posture estimation of power assist orthosis by measuring the tension of pneumatic rubber artificial muscles", Proceedings of Welfare Engineering Symposium 2007, pp.142-145, 2007.10.1-3 Shujiro Doda, “Development of small control valve for power assist and sensor integrated with artificial muscle”

  However, in the configuration of the prior art shown in FIG. 7, the direct acting potentiometer 91 does not have flexibility, so that the flexibility inherent in the direct acting telescopic actuator 92 is significantly impaired. Further, since the direct acting potentiometer 91 is large in shape, there is a problem that the efficiency in space is also deteriorated.

  In the configuration of the prior art shown in FIG. 8, the conductive rubber is generally stretchable, and it is necessary to apply a pretension in the pulling direction to the conductive rubber in advance in order to attach it to the actuator having contractibility. become. As a result, the measurement accuracy deteriorates due to the difficulty of attaching the conductive rubber to the actuator, and it is necessary to maintain the tension, and the life of the sensor (conductive rubber) is kept constant to maintain the tension. There is a problem that there is a possibility that it may deteriorate significantly. In addition, since the resistance value of the conductive rubber is generally very high, there is a problem that a good signal-to-noise ratio (S / N ratio) cannot be obtained. If the resistance value is decreased by increasing the thickness of the conductive rubber in order to improve the signal-to-noise ratio, there is a problem that the rigidity of the conductive rubber is increased and the attachment becomes more difficult.

Further, the configuration disclosed in Non-Patent Document 6 measures the displacement in the circumferential direction of the actuator, and suggests a configuration for measuring strain along the long axis direction of the actuator as in the present invention. It is not a thing. Further, the linear encoder disclosed in Non-Patent Document 6 does not measure distortion, and does not suggest the present invention in which distortion is measured by a strain sensor.
The present invention has been made in view of the above problems, and an object of the present invention is to realize a linear motion expansion / contraction actuator in which a strain sensor can be easily attached and a signal-to-noise ratio is improved.

  A linear motion expansion / contraction actuator according to the present invention includes an expansion / contraction member that can expand / contract in a long axis direction, and an elastic body that covers an outer peripheral surface of the expansion / contraction member along the circumferential direction in order to detect a circumferential expansion / contraction strain of the expansion / contraction member. And a strain sensor.

  Due to this feature, the elastic body that covers the outer circumferential surface of the elastic member along the circumferential direction detects the elastic strain in the circumferential direction of the elastic member, so that the strain sensor can be easily attached and the linear motion with improved signal to noise ratio A telescopic actuator can be realized.

  In the linear motion extendable actuator according to the present invention, it is preferable that the elastic body is made of rubber.

  According to the above configuration, an elongation strain of about 20% can be allowed and can be measured electrically relatively easily.

  In the linear motion extendable actuator according to the present invention, the elastic body is preferably made of a conductive material.

  According to the above configuration, an elongation strain of about 20% can be allowed and can be measured electrically relatively easily.

  In the linear motion expansion / contraction actuator according to the present invention, the expansion / contraction member is preferably a tube.

  According to the above configuration, the direct acting telescopic actuator can be driven by air pressure.

  In the linear motion expansion / contraction actuator according to the present invention, it is preferable that the tube expands and contracts in a major axis direction by inflow and outflow of a compressed fluid.

  According to the said structure, it can apply to a McKibben type pneumatic actuator.

  In the linear motion expansion / contraction actuator according to the present invention, it is preferable that the tube is enlarged by inflow of a medium.

  According to the said structure, the distortion of the circumferential direction of a tube becomes larger than the distortion of an axial direction, and the S / N ratio of this invention which detects the distortion of the circumferential direction improves.

  In the linear motion expansion / contraction actuator according to the present invention, the elastic body is preferably formed in an annular cross section.

  According to the said structure, an elastic body can be stably attached so that it may fit in an expansion-contraction member.

  In the linear motion expansion / contraction actuator according to the present invention, it is preferable that the strain sensor further includes a conductive wire connected to the elastic body in order to transmit a signal representing expansion / contraction strain in the circumferential direction of the expansion / contraction member.

  According to the said structure, the signal showing the expansion-contraction strain of the circumferential direction of an expansion-contraction member can be transmitted to the estimation means which estimates the expansion-contraction distortion of the major axis direction of an expansion-contraction member based on the expansion-contraction strain of the circumferential direction.

  In the linear motion expansion / contraction actuator according to the present invention, it is preferable that the linear motion expansion / contraction actuator further includes an estimation unit that estimates the expansion / contraction strain in the major axis direction of the expansion / contraction member based on the expansion / contraction strain in the circumferential direction of the expansion / contraction member detected by the strain sensor. .

  According to the said structure, the linear motion expansion-contraction actuator which can detect the expansion-contraction distortion of the longitudinal direction of an expansion-contraction member can be obtained by detecting the expansion-contraction distortion of the circumferential direction of an expansion-contraction member with a strain sensor.

  In the linear motion expansion / contraction actuator according to the present invention, the strain sensor is provided with an elastic body that covers the outer peripheral surface of the expansion / contraction member along the circumferential direction in order to detect the expansion / contraction strain in the circumferential direction of the expansion / contraction member. It is easy to realize a linear motion extendable actuator having an improved signal to noise ratio.

  An embodiment of the present invention will be described with reference to FIGS. 1 to 14B. FIG. 1 is a diagram illustrating an appearance of a linear motion extendable actuator 1 according to an embodiment. FIG. 2 is a view showing the appearance of the tube 2 provided in the linear motion extendable actuator 1. FIG. 3 is a view showing the strain sensor 3 provided in the tube 2. 4A is a front view schematically showing the strain sensor 3 provided in the tube 2, and FIG. 4B is a cross-sectional view thereof.

The present embodiment relates to a detection mechanism that performs high-precision measurement of the amount of axial displacement of a McKibben actuator driven by air pressure. In this embodiment, a sensor for measuring the displacement of a McKibben type pneumatic actuator is proposed. The McKibben type pneumatic actuator has a mechanism that contracts in the long axis direction by inflow of compressed air. Measuring the displacement of the actuator is important for precise control of the driven object. However, since the actuator has flexibility, it is not easy to measure the displacement. In the present embodiment, the strain in the circumferential direction of the McKibben actuator is measured using a flexible strain sensor, and the axial strain is estimated. Since the circumferential extension strain is larger than the axial shrinkage strain, a signal-to-noise ratio superior to that obtained by directly measuring the axial displacement is obtained.
The linear motion expansion / contraction actuator 1 includes a plurality of tubes 2 that can expand and contract in the long axis direction. The tube 2 can be a McKibben type rubber artificial muscle that expands and contracts in the longitudinal direction by inflow and outflow of a compressed fluid.

  Each tube 2 is provided with a strain sensor 3 for detecting the stretching strain in the major axis direction of the tube 2. The strain sensor 3 has an annular cross-section elastic body 4 that covers the outer peripheral surface of the tube 2 along the circumferential direction in order to detect the expansion and contraction strain in the circumferential direction of the tube 2. The elastic body 4 is made of conductive rubber. The strain sensor 3 is provided with a conducting wire 5 connected to the elastic body 4 in order to transmit a signal representing the stretching strain in the circumferential direction of the tube 2. The conducting wire 5 is connected to an estimator (not shown) that estimates the stretching strain in the long axis direction of the tube 2 based on the stretching strain in the circumferential direction of the tube 2 detected by the elastic body 4 of the strain sensor 3.

  Since the direct acting telescopic actuator 1 is flexible and lightweight, it can be used as a wearable power assist device. Further, the direct acting telescopic actuator 1 can be used for hoists, nursing beds, playground equipment, and the like. In order to improve the performance of the linear motion extendable actuator 1, highly accurate displacement measurement is essential. The strain sensor 3 is a sensor that measures the displacement of the tube 2 (actuator), and corresponds to an optical encoder in an electromagnetic motor. Since the tube 2 operating as an actuator has flexibility and has a length of several tens of centimeters along the long axis direction, there has been no suitable sensor conventionally.

FIG. 5 is a view for explaining expansion and contraction of the tube 2. FIG. 6 is a graph showing the relationship between the major axis direction shrinkage rate and the circumferential direction shrinkage rate of the tube 2. When the tube 2 contracts in the major axis direction, the tube 2 extends in the circumferential direction (diameter direction). In the graph of FIG. 6, the horizontal axis indicates the contraction rate in the long axis direction of the tube 2, and the vertical axis indicates the expansion rate in the circumferential direction of the tube 2. From FIG. 6, it can be seen that the tube 2 of the linear motion expansion / contraction actuator 1 has a larger circumferential expansion rate than the major axis direction contraction rate. For example, when the contraction rate in the long axis direction is 80.5%, the contraction rate in the circumferential direction is 149.5%.
The effective strain is ((149.5-100) / (100-80.5))
= (49.5 / 19.5)
= 2.5
Thus, the effective strain of the tube 2 according to the present embodiment is about 2.5.

  Thus, the linear motion telescopic actuator 1 according to the present embodiment includes a conductive rubber-like elastic body for estimating the strain along the axial direction of the tube 2 by detecting the circumferential strain of the tube 2. 4 is provided. When the conductive rubber elastic body 4 is attached to the tube 2, it is not necessary to apply pretension as in the configuration of the prior art. This is because the tube 2 of the linear motion expansion / contraction actuator 1 expands in the circumferential direction when contracted in the axial direction at the time of driving, but the conductive rubber-like elastic body 4 similarly extends in the circumferential direction. Accordingly, handling of the strain sensor becomes easier than in the prior art, and the life of the strain sensor is improved. In addition, the McKinben type actuator has a larger circumferential expansion rate than the long-axis direction contraction rate, and the linear motion expansion / contraction actuator 1 of the present embodiment detects not the long-axis direction contraction rate but the circumferential direction expansion rate. Therefore, the S / N ratio is improved as compared with the configuration of the prior art that detects the contraction rate in the long axis direction.

FIG. 9 is a graph showing the measurement result of the expansion / contraction strain of the tube 2, and FIG. 10 is a graph showing the measurement result of the expansion / contraction strain of the tube 2 after passing through the low-pass filter. 9 and 10, the horizontal axis indicates time, and the vertical axis indicates measurement voltage.
9 shows the voltage waveform C3 measured by the elastic body 4 of the present embodiment, the voltage waveform C2 measured by the long-axis direction direct measurement using the conductive rubber shown in FIG. 8, and the linear motion shown in FIG. A voltage waveform C4 measured by a type potentiometer is shown. The S / N ratio by the voltage waveform C3 is 14.4 (dB), the S / N ratio by the voltage waveform C2 is 3.1 (dB), and the S / N ratio by the voltage waveform C4 (reference) is , 43.8 (dB). Thus, the S / N ratio of 14.4 dB by the conductive rubber elastic body 4 that detects the strain in the circumferential direction of the tube is S / N by the conventional conductive rubber elastic body that detects the strain in the axial direction. It can be seen that the ratio was improved from 3.1 dB.

  FIG. 10 shows the voltage waveform C6 after passing through the low-pass filter measured by the elastic body 4 of the present embodiment and the voltage after passing through the low-pass filter measured by long-axis direction direct measurement using the conductive rubber shown in FIG. A waveform C5 and a voltage waveform C7 measured by the direct acting potentiometer shown in FIG. 7 are shown. The S / N ratio by the voltage waveform C6 is 28.0 (dB), the S / N ratio by the voltage waveform C5 is 17.1 (dB), and the S / N ratio by the voltage waveform C7 (reference) is 51.3 (dB). Thus, the S / N ratio of 28.0 dB by the conductive rubber elastic body 4 that detects the strain in the circumferential direction of the tube is S / N by the conventional conductive rubber elastic body that detects the strain in the axial direction. It can be seen that the ratio is improved from 17.1 dB.

  11 (a), 12 (a) and 13 (a) are front views showing a method of manufacturing the strain sensor 3, respectively. FIG. 11 (b), FIG. 12 (b) and FIG. 13 (b). Is a plan view thereof. 14A is a cross-sectional view showing the configuration of the strain sensor 3, and FIG. 14B is a perspective view showing the conductive flexible material 8a (8b) provided in the strain sensor 3. FIG.

  First, as shown in FIGS. 11 (a) and 11 (b), the tips of the two conducting wires 5 are placed on the surface of the flat strip-like conductive flexible material 8a. One of the two conducting wires 5 is placed at a distance of about one third of the laterally long length of the conductive flexible material 8a from one end of the conductive flexible material 8a. The other one of the two conducting wires 5 is placed at a distance of about one third of the laterally long length of the conductive flexible material 8a from the other end of the conductive flexible material 8a.

  Then, as shown in FIGS. 12A and 12B, the conductive adhesive 7 is applied so as to cover one tip of the two conductive wires 5 on the conductive flexible material 8a. Next, the conductive adhesive 7 is applied so as to cover the other tip of the conductive wire 5.

  Thereafter, as shown in FIGS. 13A and 13B, the conductive flexible material 8b is sandwiched between the two conductive wires 5 coated with the conductive adhesive 7 on the conductive flexible material 8a. Put it on. Then, as shown in FIG. 14A, one end and the other end of the conductive flexible materials 8a and 8b are bonded to complete a strain sensor having an elastic body 4 and a conducting wire 5 having an annular cross section.

  According to the present embodiment, the extensible conductive rubber is used for the circumferential displacement measurement of the McKibben actuator that also has the extensibility, and pre-tension is not required. As a result, the mounting becomes easy and the lifetime is improved. In addition, by utilizing the fact that the circumferential extension strain of the McKibben actuator is larger than the contraction strain in the axial direction, a signal-to-noise ratio superior to direct measurement of the axial method displacement is obtained. In addition, when the closed cross section is formed of conductive rubber so as to cover the circumferential direction of the actuator, it becomes easy to withstand the extension strain, and at the same time, the resistance value is halved and the signal-to-noise ratio is improved.

  In order to measure the axial displacement of the McKibben actuator, it is more advantageous in terms of the signal-to-noise ratio to measure the circumferential displacement with greater distortion. A displacement measuring sensor using conductive rubber is more advantageous in terms of handling if it is used for measuring a circumferential displacement having extensibility. If the closed cross section is made of conductive rubber for measuring the circumferential displacement, the resistance value can be halved and further improvement in the signal-to-noise ratio can be expected. Furthermore, the construction of the closed cross section improves robustness against elongation strain.

  In the present embodiment, an example in which the elastic body 4 is made of conductive rubber has been shown, but the present invention is not limited to this. A conductive rubber is preferable in that it can allow an elongation strain of about 20% and can be measured electrically relatively easily. However, the material is not limited to conductive rubber as long as it is a material that converts strain into an electrical signal and can measure the circumferential extension strain. For example, the elastic body 4 may be configured by a piezo element.

  Moreover, in this Embodiment, although the elastic body 4 showed the example whose cross section is cyclic | annular, this invention is not limited to this. The cross section of the elastic body 4 may not be annular.

  In the present embodiment, an example of a McKibben actuator driven by air pressure is shown, but the actuator of the present invention is not limited to air pressure. For example, the present invention can also be applied to a linear motion extendable actuator driven by liquid pressure. Further, it may be an actuator that contracts or extends by a piezoelectric actuator, a conductive polymer material, an elastomer, or a shape memory alloy. However, the advantage of the present invention appears more clearly in the pneumatic direct acting telescopic actuator.

In this embodiment,
The sensitivity (S / N ratio) is increased by utilizing the fact that the strain in the axial direction is smaller than the strain in the circumferential direction. As described above, the strain in the circumferential direction is larger than the strain in the axial direction. Only when the volume of the tube increases due to inflow.

Because if the volume of the tube does not change before and after driving,
(1- (axial strain)) × (1- (circumferential strain)) ² = 1 (Expression 1)
Must be established,
This is because the circumferential strain is smaller than the axial strain. When the above (Equation 1) holds, the circumferential strain becomes the square root of the axial strain. That is, only when the tube expands due to the inflow of the medium, the advantage of “axial strain <circumferential strain” occurs.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can be applied to a linear motion expansion / contraction actuator that expands and contracts in the major axis direction, and can also be applied to active links, welfare medical equipment, and sports training equipment. Further, the present invention can be applied to a selective training device for a muscle damage part for elderly people, an exercise equipment for elderly people, a shoe-type orthosis for ankle joint fixation for hemiplegic patients, and a motion assist device for a caregiver.

It is a figure which shows the external appearance of the linear motion expansion-contraction actuator which concerns on embodiment. It is a figure which shows the external appearance of the tube provided in the said linear motion expansion-contraction actuator. It is a figure which shows the distortion sensor provided in the said tube. (A) is a front view which shows typically the strain sensor provided in the said tube, (b) is the sectional drawing. It is a figure for demonstrating the expansion-contraction of the said tube. It is a graph which shows the relationship between the major axis direction shrinkage rate of the said tube, and the circumferential direction shrinkage rate. It is a figure for demonstrating the method to measure the distortion | strain of a linear motion expansion-contraction actuator with a linear motion type potentiometer. It is a figure for demonstrating the method to measure the distortion | strain of a linear motion expansion-contraction actuator by the long-axis direction direct measurement using conductive rubber. It is a graph which shows the measurement result of the expansion-contraction distortion of the said tube. It is a graph which shows the measurement result after the low-pass filter of the expansion-contraction distortion of the said tube. (A) is a front view which shows the manufacturing method of the said strain sensor, (b) is the top view. (A) is a front view which shows the manufacturing method of the said strain sensor, (b) is the top view. (A) is a front view which shows the manufacturing method of the said strain sensor, (b) is the top view. (A) is sectional drawing which shows the structure of the said strain sensor, (b) is a perspective view which shows the conductive flexible material provided in the said strain sensor.

Explanation of symbols

1 Direct-motion telescopic actuator 2 Tube (expandable member)
DESCRIPTION OF SYMBOLS 3 Strain sensor 4 Elastic body 5 Conductor 7 Conductive adhesive 8a, 8b Conductive flexible material

Claims (9)

A telescopic member capable of stretching in the long axis direction;
A linear motion expansion / contraction actuator, comprising: a strain sensor having an elastic body that covers an outer peripheral surface of the expansion / contraction member along the circumferential direction in order to detect expansion / contraction strain in the circumferential direction of the expansion / contraction member.   The linear motion extendable actuator according to claim 1, wherein the elastic body is made of rubber.   The linear motion telescopic actuator according to claim 1, wherein the elastic body is made of a conductive material.   The direct acting telescopic actuator according to claim 1, wherein the telescopic member is a tube.   The linear motion expansion / contraction actuator according to claim 4, wherein the tube expands and contracts in a major axis direction by inflow and outflow of a compressed fluid.   The linear motion telescopic actuator according to claim 4, wherein the tube expands by inflow of a medium.   The linear motion telescopic actuator according to claim 1, wherein the elastic body is formed in an annular cross section.   The linear motion expansion / contraction actuator according to claim 1, wherein the strain sensor further includes a conductive wire connected to the elastic body to transmit a signal representing expansion / contraction strain in a circumferential direction of the expansion / contraction member.   The linear motion expansion / contraction actuator according to claim 1, further comprising an estimation unit that estimates expansion / contraction strain in the major axis direction of the expansion / contraction member based on expansion / contraction strain in the circumferential direction of the expansion / contraction member detected by the strain sensor.