Gripping device

Abstract

The purpose of the present disclosure is to provide a gripping device that can detect gripping force accurately with high sensitivity and has a finger part with a tip portion miniaturized to be insertable into a narrow environment.　This gripping device comprises: a body part; a plurality of finger parts provided in the body part; a pressure-sensitive sensor that is provided on a gripping surface of the finger parts and detects force applied to the gripping surface; a force sensor that is provided at a root portion of the finger parts and detects force applied to the finger parts; a drive device that drives the plurality of finger parts to approach and separate from each other; and a control device that calculates a load that the finger parts receive from an object being gripped, on the basis of detection values of the pressure-sensitive sensor and the force sensor, and controls the drive device on the basis of the load.

Description

gripping device

[0001] The present disclosure relates to a gripping device that is attached to the tip of a robot arm or the like.

[0002] A gripping device that grips an object to be gripped with multiple fingers that can approach and separate from each other is provided at the tip of a robot arm, etc., and is used in various fields such as manufacturing sites. It is known that the gripping device is provided with a force sensor to grip the object to be gripped with an appropriate force, and the drive of the fingers is controlled based on the detected value.

[0003] 9 shows an example of a conventional gripping device having a force sensor (Patent Document 1). The gripping device 100 has a main body 101 attached to the tip of a robot arm or the like, and a pair of fingers 102 provided on the main body 101.

[0004] The finger portion 102 has a fingertip portion 103 whose gripping surface 104 comes into contact with the object to be gripped, a finger base portion 105 that supports the fingertip portion 103, a force sensor 106 provided between the finger base portion 105 and a slide portion 107, and the slide portion 107 that is movable in the left-right direction in the figure by a linear slider (not shown) provided on the main body portion 101 and is driven by a drive device (not shown) built into the main body portion 101.

[0005] The driving device drives the sliding portion 107 to close the pair of finger portions 102, thereby enabling the object to be grasped to be grasped by the grasping surface 104 of the fingertip portion 103. At this time, a load (gripping force) from the object to be grasped is applied to the fingertip portion 103, and the magnitude of the load is detected by the force sensor 106. Then, the driving device is controlled based on the detected load, thereby grasping the object to be grasped with a predetermined force.

[0006] 10 shows an example of another conventional gripping device having a force sensor (Patent Document 2). The gripping device 110 has a main body 111 attached to the tip of a robot arm or the like, and a pair of fingers 112 provided on the main body 111.

[0007] In this example, the force sensor 116 is provided between the fingertip 113 and the base 115. The base 115 is attached to a slide 117, which is driven by a drive unit (not shown) built into the main body 111.

[0008] The drive device drives the slide portion 117 to close the pair of fingers 112, allowing the object to be grasped to be grasped by the grasping surface 114 of the fingertip portion 113. At this time, a load (gripping force) from the object to be grasped is applied to the fingertip portion 113, and the magnitude of the load is detected by the force sensor 116. Then, the drive device is controlled based on the detected load to grasp the object to be grasped with a predetermined force.

[0009] International Publication No. 2023 / 145675 Japanese Patent Application Laid-Open No. 2023-151157

[0010] In the gripping device 100 of FIG. 9 , the load from the object to be gripped is transmitted to the force sensor 106 via the fingertip 103 and the base 105, and therefore the detection sensitivity of the force sensor 106 may be reduced due to the influence of the mass and deformation of the fingertip 103 and the base 105.

[0011] In addition, in the gripping device 110 of FIG. 10, the force sensor 116 is provided on the back of the fingertip portion 113, and therefore the detection sensitivity of the force sensor 116 is better than in the example of the gripping device 100 of FIG. 9, but the tip portion of the finger portion 112 becomes larger, making it difficult to insert the finger portion 112 into a narrow environment.

[0012] An object of the present disclosure is to provide a gripping device that can detect gripping force accurately with high sensitivity and has miniaturized finger tip portions that can be inserted into narrow environments.

[0013] The gripping device of the present disclosure includes a main body, a plurality of finger portions provided on the main body, a pressure sensor provided on the gripping surface of the finger portions and detecting the force applied to the gripping surface, a force sensor provided at the base of the finger portions and detecting the force applied to the finger portions, a drive unit that drives the plurality of finger portions to move toward and away from each other, and a control unit that determines the load that the finger portions receive from the object to be gripped based on the detection values ​​of the pressure sensor and the force sensor, and controls the drive unit based on the load.

[0014] The gripping device of the present disclosure has both a pressure sensor on the gripping surface and a force sensor at the base of the fingers, allowing it to detect gripping force accurately and with high sensitivity regardless of the magnitude of the gripping force. In addition, the miniaturization of the tip of the finger allows it to be inserted into narrow spaces, improving workability.

[0015] FIG. 1 is a diagram showing an outline of a gripping device; FIG. 2 is a diagram showing the characteristics of a pressure sensor; FIG. 3 is a diagram showing the characteristics of a force sensor; FIG. 4 is a diagram showing the characteristics of a pressure sensor and a force sensor; FIG. 5 is a diagram showing a flowchart of a control device; FIG. 6 is a diagram showing the hysteresis characteristics of a force sensor and a pressure sensor; FIG. 7 is a diagram showing the characteristics in a state where a low-pass filter is used for a sensor signal; FIG. 8 is a cross-sectional view showing a modified example of the mounting state of a pressure sensor; FIG. 9 is a diagram showing a conventional technique; FIG. 10 is a diagram showing a conventional technique.

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the components, the arrangement positions and connection forms of the components, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0017] Furthermore, each drawing is a schematic diagram and is not necessarily an exact illustration. In each drawing, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

[0018] 1 is a diagram showing an outline of a gripping device 1 according to the present disclosure. The gripping device 1 has a main body 2 attached to the tip of a robot arm or the like, and a pair of fingers 3 provided on the main body 2.

[0019] The finger portion 3 has a fingertip portion 4 for gripping an object to be gripped, and a base portion 6 for supporting the fingertip portion 4. A sheet-like pressure sensor 7 is attached to the entire gripping surface 5 of the fingertip portion 4, and detects the load received from the object to be gripped when the fingertip portion 4 comes into contact with the object. The base portion 6 is attached to a slide portion 9 via a force sensor 8. The force sensor 8 is provided midway along the force transmission path that transmits the load received by the fingertip portion 4 to the main body portion 2 that supports the finger portion 3.

[0020] The slide portion 9 is provided so as to be slidable in the left-right direction in the figure along a linear slider (not shown) provided on the main body portion 2. A drive device (not shown) is provided on the main body portion 2, and the slide portion 9 is moved in the left-right direction by the drive device. The operation of the drive device is controlled by a control device (not shown).

[0021] The pressure sensor 7 is a sheet-like sensor that detects the pressure received from the object to be grasped when it comes into contact with the object, and can be, for example, a sheet-like pressure sensor whose electrical resistance changes when pressure is applied. Then, by determining in advance the relationship between the load applied to the pressure sensor and the change in electrical resistance, the load can be determined from the amount of change in electrical resistance.

[0022] Generally, sheet-type pressure sensors have the property that they are sensitive to low loads (low pressures) and become less sensitive as the load increases. Figure 2 is a graph showing the relationship between the load applied to the pressure sensor 7 (true load) and the load detected by the pressure sensor 7 (measured load).

[0023] In graph 10, when the true load is between 0 and f1, the true load and the measured load are proportional to each other and have the same value (first straight line portion 11). When the true load is greater than f1, the measured load does not increase as much as the true load (curved line portion 12). When the true load is greater than f2, the measured load hardly increases even when the true load increases (second straight line portion 13). First straight line portion 11 and curved line portion 12 are connected at first connection point 14, and curved line portion 12 and second straight line portion 13 are connected at second connection point 15. Here, the values ​​of f1 and f2 generally differ depending on the type and size of the pressure sensor.

[0024] When the true load is smaller than f1, the pressure sensor is sensitive enough to accurately detect the true load (first straight section 11), but when the true load is larger than f1, the pressure sensor becomes less sensitive and detects a value smaller than the true load as the measured load (curved section 12, second straight section 13).

[0025] The force sensor 8 is a sensor that is provided in the force transmission path between the fingertip portion 4 and the slide portion 9 and detects the external force acting on the fingertip portion 4. A load cell provided on the surface of a member that constitutes the finger portion 3, or a displacement sensor that measures the displacement when a part of the finger portion 3 is deformed by an external force, can be used.

[0026] Generally, a force sensor has a property that its sensitivity is poor when the load is low and that its sensitivity increases as the load increases. Figure 3 is a graph showing the relationship between the load applied to the force sensor 8 (true load) and the load detected by the force sensor 8 (measured load).

[0027] In graph 20, the measured load is almost zero when the true load is between 0 and f3 (third linear section 21). Then, at third connection point 22, the increase in the true load and the increase in the measured load become proportional (fourth linear section 23).

[0028] When the true load is smaller than f3, the force sensor 8 detects a small value relative to the true load as the measured load value (third linear section 21), but when the true load is larger than f3, the force sensor 8 can accurately detect the true load (fourth linear section 23).Incidentally, since the magnitude of f3 is generally negligible, the value output by the force sensor 8 may be used as the load value as is.

[0029] Based on the above characteristics of the pressure sensor 7 and the force sensor 8, in the gripping device 1 of the present disclosure, when the true load is small, the measurement value from the pressure sensor 7 is adopted as the value of the load from the object to be gripped, and when the true load is large, the measurement value from the force sensor 8 is adopted as the value of the load to control the drive device.

[0030] 4 is a diagram in which a graph 10 of the pressure sensor 7 and a graph 20 of the force sensor 8 are superimposed. If the value of the true load at the first connection point 14 where the first straight portion 11 and the curved portion 12 connect is F1max, and the value of the true load at the third connection point 22 where the third straight portion 21 and the fourth straight portion 23 connect is F2min, the true load can be accurately measured by the pressure sensor 7 up to the true load F1max, and the true load can be accurately measured by the force sensor 8 when the true load is F2min or greater.

[0031] In the gripping device 1 of the present disclosure, thresholds F1 and F2 are set so that F1max≧F1, F2min≦F2 and F1>F2, and the measurement value of either the pressure sensor 7 or the force sensor 8 is adopted as the load value based on this threshold, as shown below.

[0032] 5 shows the operation flow of the control device when gripping an object to be gripped with the gripping device 1. First, the force detection mode is set to "pressure sensitive" (step S1). Here, the force detection mode indicates whether the measurement value of the pressure sensor 7 or the force sensor 8 is to be used; in "pressure sensitive," the measurement value of the pressure sensor 7 is used, and in "force," the measurement value of the force sensor 8 is used.

[0033] When the control device controls the drive device to start the gripping operation, the control device acquires the detection value Fa from the pressure sensor 7 (step S2) and also acquires the detection value Fb from the force sensor 8 (step S3).

[0034] If the detection mode is "pressure sensitive" (step S4: yes), the control device compares the magnitude of the detected value Fa with a predetermined threshold value F1, and if the detected value Fa is smaller than the threshold value F1 (step S5: yes), the detected value Fa is set as the value of the load F from the object to be grasped (step S6). On the other hand, if the detected value Fa is equal to or greater than the threshold value F1 (step S5: no), the detection mode is changed to "force" (step S7), and the detected value Fb is set as the value of the load F (step S8).

[0035] If step S4 is no (detection mode is "force"), the control device compares the magnitude of the detected value Fb with a predetermined threshold value F2, and if the detected value Fb is greater than the threshold value F2 (step S9 is yes), the detected value Fb is set as the value of the load F from the object to be grasped (step S10). On the other hand, if the detected value Fb is equal to or less than the threshold value F2 (step S9 is no), the detection mode is changed to "pressure-sensitive" (step S11), and the detected value Fa is set as the value of the load F (step S12).

[0036] Once the value of the load F is determined, the control device controls the drive device based on the value of the load F to grip the object to be gripped with the desired gripping force (step S13).

[0037] The control device determines whether the gripping operation has ended (step S14), and if not (no in step S14), returns to step S2 to repeat the above operation to continue the gripping operation. On the other hand, if the gripping operation has ended (yes in step S14), the operation ends.

[0038] FIG. 6 is a diagram illustrating the load F acquired by the control device when the gripping device 1 grips an object to be gripped based on the operational flow of FIG. 5 . When nothing is being gripped, operation begins with the force detection mode set to "pressure-sensitive." As the fingers 3 close and the gripping surfaces 5 of the fingertips 4 come into contact with the object to be gripped, the fingertips 4 receive a load from the object to be gripped. When the load is less than F2 min, the pressure sensor 7 detects the load along the first linear portion 11, while the force sensor 8 detects almost no load along the third linear portion 21. Therefore, the control device uses the detected value Fa from the pressure sensor 7 as the value of the load F. Until the true load reaches a predetermined threshold value F1, the detected value Fa from the pressure sensor 7 along the first linear portion 11, as indicated by arrow 25, is used as the value of the load F.

[0039] When the distance between the fingertips 4 narrows and the true load exceeds F1, the control device changes the detection mode to "force," and as shown by arrow 26, the control device adopts the detection value Fb from the force sensor 8 as the value of the load F instead of the detection value Fa from the pressure sensor 7.

[0040] When the distance between the fingertips 4 becomes narrower and the true load becomes larger, the control device adopts the detection value Fb from the force sensor 8 along the fourth straight portion 23 as the value of the load F, as shown by the arrow 27 .

[0041] On the other hand, when the fingers 3 are opened to release the grasped object, the true load gradually decreases as the fingers 3 are opened. When the true load is large, the detection value Fb of the force sensor 8 along the fourth linear portion 23, as shown by the arrow 28, is adopted as the value of the load F.

[0042] When the distance between the fingertips 4 increases and the true load falls below F2, the control device changes the detection mode to "pressure-sensitive," and as shown by arrow 29, the control device adopts the detection value Fa from the pressure sensor 7 as the value of the load F instead of the detection value Fb from the force sensor 8.

[0043] When the distance between the fingertips 4 increases further and the true load decreases further, the control device adopts the detection value Fa from the pressure sensor 7 along the first straight portion 11 as the value of the load F, as shown by the arrow 30.

[0044] The values ​​of F1 and F2 relative to F1max and F2min are determined, for example, as follows: F1=F2min+(F1max-F2min)*0.75 F2=F2min+(F1max-F2min)*0.25

[0045] In this way, a hysteresis characteristic is provided for selecting which measurement value from the pressure sensor 7 or the force sensor 8 to use when the grip force changes, so that frequent switching between the pressure sensor 7 and the force sensor 8 does not occur when the grip force increases or decreases slightly, thereby stabilizing the measurement and control of the finger portion 3.

[0046] When switching between the signals of the pressure sensor 7 and the force sensor 8, the measured loads determined by each sensor are different, which can cause large discontinuous changes in the value and lead to unstable gripping by the gripping device 1. Therefore, a low-pass filter is applied to the detection signal to suppress the high-frequency components of the signal change and smooth the change in the measured load. To achieve both stable gripping and high responsiveness, the cutoff frequency is selected to be as high as possible without causing unstable gripping, for example, 10 Hz.

[0047] 7 is a graph showing an example of how the detection signal changes when switching from the pressure sensor 7 to the force sensor 8 as the measurement load increases. When the load is below threshold F1, the pressure sensor 7 detects values ​​along the first linear portion 11 of graph 10 (arrow 33). When the load exceeds F1, the detection mode is changed to "force," and the detected value smoothly transitions along curve 34 to graph 20 of the force sensor 8 (arrow 34). As the load increases further, the load is detected along the fourth linear portion 23 of graph 20 (arrow 35).

[0048] Although not shown, the detection signal resulting from switching from the force sensor 8 to the pressure sensor 7 as the measurement load decreases also changes smoothly by applying a low-pass filter. That is, when the load decreases along the fourth linear portion 23 and becomes smaller than the threshold value F2, the detected value smoothly shifts to the graph 10 of the pressure sensor 7, and as the load decreases further, the load is detected along the first linear portion 11 of the graph 10.

[0049] As a result, when the detection mode changes from "pressure sensitive" to "force" or from "force" to "pressure sensitive," the detected load value changes smoothly without abrupt changes. Therefore, the drive of the drive device by the control device does not change abruptly, and the grip of the object to be gripped is stable.

[0050] 8 is a diagram showing a modified structure for attaching the pressure sensor 7 to the fingertip 4. The pressure sensor 7 has a sheet-like sensor portion 41 and a support portion 42 that supports the sensor portion 41. A frame portion 43 is formed on the periphery of the support portion 42 so as to surround the sensor portion 41.

[0051] If a pressure sensor 7 having such a structure is attached to a flat gripping surface 5, when gripping an object that is larger than the width of the sensor portion 41, the object to be gripped may interfere with the frame portion 43, making it impossible to accurately measure the pressure. Therefore, as shown in Figure 8, the gripping surface 5 is formed to be curved in a convex shape, and the pressure sensor 7 is curved along the curved gripping surface 5 and attached.

[0052] With this structure, even when grasping an object that is wider than the sensor unit 41, the maximum stroke S can be measured up to the thickness of the sensor unit 41 as shown by the dotted line without interfering with the frame unit 43.

[0053] The gripping device of the present disclosure has been described above, but the present disclosure is not limited to the above embodiment. In the above example, the finger portion has a pair of fingertips, but the fingertip portion may be three or more. Furthermore, various drive devices can be used for opening and closing the finger portion. The pressure sensor is not limited to a specific type as long as it can measure the force (pressure) when the object to be gripped comes into contact with the sensor. Furthermore, the force sensor is not limited to a specific type as long as it can measure the force acting on the finger portion.

[0054] In addition, the specific configuration and shape of the gripping device can be combined and changed as appropriate.

[0055] The present invention can be suitably used as a gripping device to be attached to the tip of a robot hand, etc.

[0056] This application is based on Japanese Patent Application No. 2024-103951 filed on June 27, 2024, the entire contents of which are incorporated herein by reference.

[0057] DESCRIPTION OF SYMBOLS 1 Grip device 2 Main body 3 Finger 4 Fingertip 5 Grip surface 6 Finger base 7 Pressure sensor 8 Force sensor 9 Slider

Claims

1. A gripping device having a main body, a plurality of finger portions provided on the main body, a pressure sensor provided on the gripping surfaces of the finger portions and detecting the force applied to the gripping surfaces, a force sensor provided at the bases of the finger portions and detecting the force applied to the finger portions, a drive unit that drives the plurality of finger portions to move toward and away from each other, and a control unit that determines the load that the finger portions receive from a gripping object based on the detection values ​​of the pressure sensor and the force sensor, and controls the drive unit based on the load.

2. The gripping device according to claim 1, wherein the control device selects the detection value of either the pressure sensor or the force sensor based on the detection values ​​of the pressure sensor and the force sensor to determine the load.

3. The gripping device according to claim 2, wherein the control device changes the selection from one of the pressure sensor and the force sensor to the other so as to have a hysteresis characteristic.

4. A gripping device according to claim 2 or 3, wherein the control device uses a low-pass filter on the detected values ​​of the pressure sensor and the force sensor when changing the selection from one of the pressure sensor and the force sensor to the other.

5. A gripping device as described in claim 1, wherein the pressure sensor has a sheet-like sensor section and a support section having a frame section that supports the sensor section and surrounds the periphery of the sensor section, the gripping surface is formed to be convexly curved, and the pressure sensor is curved along the gripping surface.

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