JP2020093335A - Sensor mechanism for robot hand - Google Patents

Abstract

To provide a sensor mechanism for a robot hand that can detect states of contact of finger tips with both of an environment face and an object to be gripped.SOLUTION: The sensor mechanism for a robot hand according to the embodiment comprises: finger tip parts; first tactile sensors, arranged on surfaces at back sides of the finger tip parts, which detect contact force against an environment face on which an object to be gripped is placed; and second tactile sensors, arranged on surfaces at belly sides of the finger tip parts, which detect contact force against the object to be gripped.SELECTED DRAWING: Figure 6

Description

The present invention relates to a sensor mechanism for a robot hand.

Conventionally, in a factory where mass production has been mainstream, automation has advanced due to the spread of robot hands that repeat simple operations, that is, operations that are suitable for one object. As a result, human beings can contribute to the lack of manpower without doing dangerous work. However, in recent years, high-mix low-volume production has become mainstream, and there is a demand for a robot hand capable of performing a plurality of operations such as gripping, carrying, and assembling various objects in a limited space. For example, a problem in the gripping work of the robot hand is that it is difficult to grip a soft object or a small object whose shape changes. Here, the "soft material" includes a material that returns to its original shape when the external force is removed and a material that does not return (elastic and plastic material) when the external force is applied and deformed. It is very easy for us humans to grasp soft objects (it is unconsciously done), but it is difficult for robot hands to grasp soft objects without damaging them. Prior art documents of robot hands include, for example, the following patent documents 1 to 3 and non-patent documents 1 and 2.

International Publication No. 2009/144767 JP, 2006-297542, A JP, 2005-349492, A

M. Shimojo, T.; Araki, S.; Teshigawara, A.; Ming and M. Ishikawa, "A net-structure tactile sensor covering free-form surface and enquiring high-speed response," Proc. 2007 IEEE/RSJ Int. conf. on Intelligent Robots and Systems, pp. 670-675, 2007. Y. Suzuki, "Multilayered Center-of-Pressure Sensor for Robot Fingers and Adaptable Feedback Control," IEEE Robotics and Automation. 2, Issue 4, pp. 2180-2187, 2017.

The applicant of the present application is effective in detecting the contact state of both the environmental surface and the grasped object with respect to the fingertip when grasping a grasped object such as a soft object or a small object with high accuracy by a robot hand. I got the knowledge.

The present invention has been made in view of the above, and an object of the present invention is to provide a sensor mechanism for a robot hand capable of detecting the contact state of both the environmental surface and the grasped object with respect to the fingertip.

In order to solve the above-mentioned problems and to achieve the object, the present invention is a sensor mechanism for a robot hand, which is arranged on a fingertip portion and a surface on the back side of the fingertip portion, and an object to be grasped is placed. A first tactile sensor for detecting a contact force with respect to an environment surface; and a second tactile sensor arranged on the ventral surface of the fingertip portion for detecting a contact force with respect to the grasped object. May be.

Further, according to a preferred aspect of the present invention, the fingertip may have a step formed between the back side and the abdomen side, and the back side may be formed higher than the abdomen side.

Further, according to a preferred aspect of the present invention, the step of the fingertip portion may be formed in a bifurcated shape.

Further, according to a preferred aspect of the present invention, the fingertip portion may have a curved shape in a side view.

Further, according to a preferred aspect of the present invention, in the first and second tactile sensors, the pressure sensitive portion may be formed in a sheet shape.

According to a preferred aspect of the present invention, the first and second tactile sensors are resistance type, piezoelectric type, magnetic type, capacitance type, strain gauge type, ultrasonic type, atmospheric pressure type, hydraulic type, It may be a charge type, a crystal oscillator type, or an optical type.

According to the present invention, it is possible to detect the contact state of both the environmental surface and the grasped object for the fingertip.

FIG. 1 is a schematic diagram for explaining an approach operation of the robot hand according to the present invention to approach the environment. FIG. 2 is a schematic diagram for explaining an environmental tracing operation of the robot hand according to the present invention. FIG. 3 is a diagram showing an outline of the configuration of the robot hand according to the present embodiment. FIG. 4 is an enlarged view of the hand unit of FIG. FIG. 5 is a block diagram showing the control system of the robot hand according to the present embodiment. FIG. 6 is a schematic perspective view of the fingertip portion. FIG. 7 is a schematic side view of the fingertip portion. FIG. 8 is a schematic side view showing a state in which the fingertip of the fingertip portion is in contact with the environment surface and the grasped object. FIG. 9 is a schematic diagram for explaining the joint angles of the first joint portion and the second joint portion of the finger. FIG. 10 is a diagram for explaining the outline of the control of the overall operation of the control unit when the robot hand grips the grip target. FIG. 11 is a flow chart for explaining the detailed contents of the operation for approaching the environment side of FIG. FIG. 12 is a flowchart for explaining the detailed content of the operation of approaching the gripping target object of FIG. 10. FIG. 13-A is a diagram for explaining an example of a gripping target object according to the present embodiment. FIG. 13-B is a diagram for explaining an example of the grasped object of the present embodiment.

Embodiments of a sensor mechanism for a robot hand according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to this embodiment.

(1. Principle of the present invention)
First, the principle of the robot hand according to the present invention will be described with reference to FIGS. 1 and 2.

[1-1. background]
In developing a robot hand for the purpose of grasping and transporting an object, what becomes a problem when developing is a method of approaching and grasping various types of grasping objects in consideration of the surrounding environment. There are two factors that make this problem very difficult to solve.

The first is the environment that allows the robot to approach, transport, and move the robot to its initial position so that it does not collide with the surrounding environment of the robot, and that enables stable grasping of the grasped object using the environment. It is an operation according to the environment of. The second is to determine an appropriate force and holding method according to the size, shape, and softness of the grasped object. It is very easy for us humans to perform these actions (unconsciously), but it is difficult for the robot to judge how to approach various gripping objects.

The present invention uses a three-fingered robot hand as an example, and grasps an environment surface and a grasped object at the same time based on information obtained from tactile sensors provided on the ventral and dorsal sides of each fingertip. The purpose is to do. Here, the environment surface includes a stationary surface and a moving surface such as a work table, a table table, and a belt conveyor. Tactile sensors are provided on the ventral and dorsal sides of each fingertip, the backside mainly detects contact with the environment surface, and the ventral side mainly detects the grasped object, thereby detecting the environment surface and the grasped object. It enables simultaneous detection.

Accordingly, in the present invention, the finger can be moved while being in contact with the environment surface, and at the same time, a stable gripping target object can be gripped. The present invention proposes a newly developed structure of a tactile sensor for a fingertip of a robot hand and a grip control method for a grip target on an environmental surface using the structure.

[1-2. Fingertip tactile sensor]
The structure of the tactile sensor of the fingertip used in the robot hand system of the present invention will be described. The main feature of this tactile sensor is that the surface of the fingertip is divided into the ventral side and the dorsal side and two sheet-shaped tactile sensors are mounted. Each tactile sensor employs a CoP (Center of Pressure) method (see Non-Patent Documents 1 and 2) that calculates and outputs the position of the center of gravity of the load distribution acting on the planar pressure-sensitive portion.

The size of the fingertip of the robot hand can be determined according to the size of the robot hand. The shape seen from the side was constructed by combining arcs. This is to ensure that the fingertips make smooth contact with the environment such as a table. Since the shape is extruded linearly in the width direction, the surface of the fingertip can be developed into a rectangle. Thereby, the tactile sensor formed on the flexible substrate can be mounted without distortion.

Two sheet-shaped tactile sensors mounted on the fingertip detect the contact state between the environmental surface and the object to be grasped on the environmental surface. The two tactile sensors have pressure-sensitive portions at two positions from inside the groove to the base of the fingertip portion on the ventral side and on the back side to a position beyond the most swollen portion. By appropriately controlling the posture of the fingertip with respect to the environment, it becomes possible to individually sense the environment surface and the grasped object.

[1-3. Control algorithm]
When a multi-fingered robot hand grasps an object to be grasped on an environment surface, a state where a fingertip simultaneously contacts both of them may occur. In particular, when the object to be grasped is small or when an operation such as scooping is required, or when a plurality of objects to be grasped are collected and simultaneously grasped, it is difficult to avoid contact with the environment in which they are placed. Therefore, in the present invention, by utilizing the output of the tactile sensor on the back side of the fingertip for the purpose of detecting contact with the environmental surface, avoidance of contact with excessive force with the environmental surface and tracing operation of the fingertip with respect to the environmental surface. I implemented a method to do.

[1-3-1. Environmental approach operation]
FIG. 1 is a schematic diagram for explaining an approach operation (a feedback operation based on the output of a tactile sensor on the back side) to the environmental surface of a robot hand according to the present invention. (A) is a case where the environment surface (for example, a workbench) is horizontal, and (B) is a case where the environment surface is inclined.

In FIG. 1, the posture angle of the fingertip portion 2 is adjusted so that the lowest point of the fingertip portion 2 of the robot hand 1 is included in the area covered by the tactile sensor on the back side in the initial posture. When it is detected that the output of the dorsal tactile sensor exceeds the threshold value after the approach operation starts, the second flexion joint (finger base side) is expanded outward and the first flexion joint (finger tip side) has the same displacement angle. Just try to close it inwards.

As a result, as shown in FIG. 1B, even if an approach is made in an inclined posture with respect to the environment surface 3, the posture of the fingertip portion 2 is kept constant and the environment of the fingertip portion 2 of each finger is kept constant. The contact force can be maintained below the threshold value, and the approach operation can be stopped when all the fingertips come into contact with each other.

[1-3-2. Environmental tracing operation]
FIG. 2 is a schematic diagram for explaining the tracing operation on the environment of the robot hand according to the present invention (feedback operation based on the output of the tactile sensor on the back side).

As shown in FIG. 2, in the present invention, as a basic operation, trajectory control is performed in which the contact point of the fingertip 2 moves horizontally at a constant speed, and in the course of that trajectory is controlled according to the output value of the tactile sensor on the back side. Correct the vertical component of so that the contact force falls within a certain range. By using this operation, the distance between the fingertips of the fingers facing each other is narrowed to grip the gripping target on the environmental surface. At this time, the posture of the fingertip portion 2 changes in the direction of bending inward, but since the tactile sensor is mounted so as to cover a wide area on the back side of the fingertip, as long as the fingertip is in contact with the environment surface 3, The tactile sensor was made to respond.

Hereinafter, an embodiment to which the robot hand according to the present invention is applied will be described. Although the components of the present invention are generally shown in the drawings herein, it will be readily understood that a wide variety of arrangements and designs may be made in various configurations. Accordingly, the following more detailed description of embodiments of the apparatus, systems and methods of the present invention is not intended to limit the scope of the invention as set forth in the claims, merely an example of selected embodiments of the invention. FIG. 4 is merely a representation of selected embodiments of devices, systems and methods consistent with the invention as claimed in this specification. Those skilled in the art will understand that the invention may be practiced without one or more of the specific details or with other methods, components, materials.

(2. Embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. In order to facilitate understanding of the description, the same reference numerals are given to the same constituent elements in each drawing as much as possible, and redundant description will be omitted.

[2-1. Robot hand configuration]
FIG. 3 is a diagram showing an outline of the configuration of the robot hand according to the present embodiment. FIG. 4 is an enlarged view of the hand portion of the robot hand. FIG. 5 is a block diagram showing the control system of the robot hand according to the present embodiment.

As shown in FIG. 3, the robot hand 10 according to the present embodiment roughly includes an arm unit 20, a hand unit 30, a base unit 40, and a control unit 50. The base portion 40 is a portion to which the arm portion 20 is attached, and can be configured by, for example, a base stand. The base portion 40 is not limited to this, and may have any configuration as long as the arm portion 20 can be attached to the base portion 40. For example, the base portion 40 may be formed of another portion such as a torso portion of a humanoid robot.

The arm unit 20 can be composed of, for example, a single-arm robot arm, and has multiple degrees of freedom (in the example shown in FIG. 3, all six degrees of freedom) with respect to the base unit 40. The arm portion 20 has, for example, six joint portions 21 to 26 that can be swung in the direction of the arrow, and servo motors 21M to 26M (see FIG. 5) are built in each joint portion 21 to 26.

The hand unit 30 is attached to the arm unit 20 and has multiple degrees of freedom with respect to the arm unit 20 (in the example shown in FIGS. 3 and 4, all eight degrees of freedom). As shown in FIGS. 3 and 4, the hand unit 30 includes a single finger 60, two fingers 70, 80, and fingers 60, 70, 70, 80, which face each other in a direction of gripping a grip target on an environmental surface. And a hand body 31 to which 80 is attached.

Each finger 60, 70, 80 has a fingertip portion 61, 71, 81, an intermediate portion 62, 72, 82, a root portion 63, 73, 83, a fingertip portion 61, 71, 81 and an intermediate portion 62, 72,. The first joint portions 64, 74, 84 provided between 82 and the second joint portions 65, 75, 85 provided between the intermediate portions 62, 72, 82 and the root portions 63, 73, 83. I have it. Servo motors 64M, 74M, 84M are built in the first joint portions 64, 74, 84 (see FIG. 5). Further, servo motors 65M, 75M, 85M are built in the second joint portions 65, 75, 85 (see FIG. 5).

Further, third joints 76, 86 are provided between the bases 73, 83 of the fingers 70, 80 on the two-finger side and the hand body 31. Servo motors 76M and 86M are built in the third joint portions 76 and 86 (see FIG. 5). For example, when the object to be grasped is a spherical object or a large object, it can be suitably grasped by turning the third joint portions 76 and 86.

The fingertip portions 61, 71, 81 of the fingers 60, 70, 80 are respectively provided with first tactile sensors 61A, 71A, 81A on the back side and second tactile sensors 61B, 71B, 81B on the ventral side. Are arranged. The first tactile sensors 61A, 71A, 81A are for detecting the contact force of the fingertips 61, 71, 81 with respect to the environment surface on which the object to be grasped is placed. The second tactile sensors 61B, 71B, 81B are for detecting the contact force of the fingertips 61, 71, 81 with respect to the grasped object on the environment surface.

As shown in FIG. 5, the control system of the robot hand 10 includes a control unit 50 that controls the overall operation of the robot hand 10 and a motor driver that drives the servo motors 21M to 26M of the joints 21 to 26 of the arm unit 20. 51, the servo motors 64M, 74M, 84M of the first joint portions 64, 74, 84 of the hand portion 30, the servo motors 65M, 75M, 85M of the second joint portions 65, 75, 85, and the third joints. The motor driver 52 that drives the servo motors 76M and 86M of the units 76 and 86, and the first tactile sensors 61A, 71A, and 81A that output the current value Iall to the control unit 50 as a sensor output according to the contact force (pressure), respectively. And second tactile sensors 61B, 71B, 81B and the like.

The control unit 50 includes, for example, a CPU, a memory, a storage, an A/D converter, a D/A converter, a power supply circuit, and the like. The CPU controls the robot hand 10 as a whole by executing a control program stored in the storage. The control unit 50 also controls the power supply circuit to supply drive power to each unit of the robot hand 10. The memory is a writable memory including a cache memory and a RAM, and is used as a read area for the CPU execution program and a work area for writing the processing data of the execution program. The storage is, for example, SSD, HDD, ROM, etc., and has a function of storing a control program, data, and the like.

The control unit 50 controls the motor driver 51 to control the motions of the servomotors 21M to 26M of the arm unit 20 to control the motions of the joint units 21 to 26 and control the overall motion of the arm unit 20. To do.

The control unit 50 also controls the motor driver 52 to control the movements of the servo motors 64M, 74M, 84M, 65M, 75M, 85M, and 76M, 86M of the hand unit 30 to thereby control the first joint. It controls the operations of the parts 64, 74, 84, the second joint parts 65, 75, 85, and the third joint parts 76, 86, and controls the overall movement of the hand part 30.

Specifically, the control unit 50 controls each joint angle of the hand unit 30 and the arm unit 20 based on the current value Iall of the first tactile sensors 61A, 71A, 81A and the second tactile sensors 61B, 71B, 81B. , The optimum values of the angular velocity, the torque, the path, etc. are calculated in real time, and the servo motors 21M to 26M of the arm unit 20 and the servo motors 64M, 74M, 84M and 65M of the hand unit 30 are calculated via the motor drivers 51 and 52. , 75M, 85M, and 76M, 86M output command values.

In the following description, when the control of the control unit 50 is described, the description of the operation via the motor driver and the servo motor is omitted for simplification of the description.

In the control unit 50, in the initial posture of the robot hand 10, the lowest points of the fingertips 61, 71, 81 of the fingers 60, 70, 80 are included in the detectable areas of the first tactile sensors 61A, 71A, 81A. Thus, the posture angles of the fingertips 61, 71, 81 are adjusted. The control unit 50 lowers the robot hand 10 to approach the environment surface, based on the sensor outputs of the first tactile sensors 61A, 71A, 81A of the fingers 60, 70, 80, respectively. , 80 are controlled so that the contact force of the fingertip portions 61, 71, 81 with respect to the environment surface becomes a predetermined value. The control unit 50 moves at least one of the fingers 60, 70, and 80 on the environmental surface in a direction to reduce the distance between the facing fingers in the operation of approaching the grasped object, and at the time of movement, The contact force of the fingertip to be moved with respect to the environmental surface is controlled to be a predetermined value. When the output of the second tactile sensor of at least one of the fingers 60, 70, 80 is equal to or greater than the threshold value, the control unit 50 determines that the grip target is gripped, and determines the grip target. Control to move to the target position.

Further, the control unit 50 adjusts the joint angles of the first joint portions 64, 74, 84 and the second joint portions 65, 75, 85 of the fingers 60, 70, 80, and the fingertip portions 61, 71, The contact force of 81 with respect to the environment surface may be controlled to be a predetermined value.

[2-2. Sensor mechanism]
Next, the sensor mechanism (first tactile sensor and second tactile sensor) of the robot hand 10 will be described with reference to FIGS. 6 to 8. Since the sensor mechanisms of the fingertip portions 61, 71, 81 have the same configuration, the fingertip portion 61 will be described as a representative. FIG. 6 is a schematic perspective view of the fingertip portion, FIG. 7 is a schematic side view of the fingertip portion, and FIG. 8 is a schematic side view showing a state where the fingertip of the fingertip portion is in contact with the environment surface and the grasped object. It is a figure.

6 to 8, the sensor mechanism is disposed on the surface of the fingertip portion 61 and the back side (back portion of the finger) of the fingertip portion 61, and is used for detecting the contact force with respect to the environment surface on which the gripping target is placed. One tactile sensor 61A and a second tactile sensor 61B that is arranged on the surface of the fingertip portion 61 on the ventral side (abdomen of the finger) and that detects the contact force with respect to the object to be grasped are provided.

The fingertip portion 61 has a curved shape in a side view, and has a configuration in which arcs are combined on the ventral side and the dorsal side. This allows the fingertip to make smooth contact with the environment. Further, the tip of the fingertip portion 61 has a bifurcated shape 61c, and the bifurcated shape 61c forms a step between the back side and the abdominal side. Both ends of the bifurcated shape 61c extend linearly in the width direction. This step is formed so that the back side is higher than the abdominal side because the first tactile sensor 61A arranged on the back side detects the environment surface. This is because by adjusting the posture angle of the fingertip portion 61, only the tip on the back side contacts the environment surface and the tip on the ventral side does not contact the environment surface.

In the first tactile sensor 61A and the second tactile sensor 61B, the pressure-sensitive portion is formed in a sheet shape, and for example, resistance type, piezoelectric type, magnetic type, capacitance type, strain gauge type, ultrasonic type Various types such as a pressure type, a hydraulic type, a charge type, a crystal oscillator type, and an optical type can be used. The sheet-shaped pressure sensitive portions of the first tactile sensor 61A and the second tactile sensor 61B can be fixed to the fingertip portion 61 by, for example, pasting.

The sheet-shaped pressure-sensitive portion of the first tactile sensor 61A extends from the inside of the groove of the bifurcated shape 61c of the fingertip portion 61 to the most swollen portion on the back side so as to cover the tip portion on the back side. It extends planarly up to the position. As described above, the second tactile sensor 61B is mounted so as to cover a wide range, so that the contact force can be detected as long as the fingertip is in contact with the environment surface.

The pressure-sensitive portion formed in the sheet shape of the second tactile sensor 41B is planar from the inside of the groove of the bifurcated shape 61c of the fingertip portion 61 to the position of the root of the ventral side so as to cover the tip of the ventral side. It is growing.

The first tactile sensor 61A and the second tactile sensor 61B can employ a CoP (Center of Pressure) method that calculates and outputs the position of the center of gravity of the load distribution acting on the pressure-sensitive portion.

[2-3. Control algorithm]
Next, a control algorithm by the control unit 50 of the robot hand 10 will be described with reference to FIGS. 9 to 12. FIG. 9 is a schematic diagram for explaining the joint angles of the first joint portion and the second joint portion of the finger. FIG. 10 is a diagram for explaining the outline of control of the overall operation of the control unit 50 when the robot hand 10 grips the grip target.

In FIG. 9, the angle of the fingertip portions 61, 71, 81 in the closing direction (the rotation angle of the first joint portions 64, 74, 84 in the closing direction) with respect to the center line of the intermediate portions 62, 72, 82 is the joint angle θ1. Called. Further, the angle of the intermediate portions 62, 72, 82 in the opening direction (the rotation angle of the second joint portions 65, 75, 85 in the opening direction) with respect to the center line of the root portions 63, 73, 83 is referred to as a joint angle θ2. ..

With reference to FIG. 10, an outline of control of the overall operation of the control unit 50 when the robot hand 10 grips a gripping target will be described. In FIG. 10, first, the initial posture of the robot hand 10 is adjusted (step S1). In the adjustment of the initial posture, the lowest points (finger tips on the back side) of the finger tips 61, 71, 81 of the fingers 60, 70, 80 of the hand section 30 are the detectable areas of the first tactile sensors 61A, 71A, 81A. Adjust the posture angle to be included in. Specifically, as shown in FIG. 9, in the initial posture, the contact point of each finger 60, 70, 80 with the environment surface becomes the first tactile sensor at the tip of the fingertip portion, and the fingertip portion 61, The joint angles (θ1, θ2) are adjusted so that 71, 81 and the intermediate portions 62, 72, 82 bend outward.

Next, the operation of approaching the environment (robot hand lowering operation) is executed (step S2). Specifically, based on the sensor outputs of the first tactile sensors 61A, 71A, 81A of the respective fingers 60, 70, 80, the entire robot hand 10 has the fingertip portions 61, 71, 81 of the respective fingers 60, 70, 80. It is controlled so that the contact force with respect to the environment surface becomes a predetermined value.

Subsequently, the operation of approaching the grasped object is executed (step S3). Specifically, each of the fingers 60, 70, 80 is moved on the environment surface in a direction of reducing the distance between the facing fingers, and at the time of movement, the fingertip portions 61, 71 of the fingers 60, 70, 80 to be moved. Feedback control is performed so that the contact force of 81 with respect to the environment surface becomes a predetermined value, and output of the second tactile sensors 61B, 71B, 81B of the fingers 60, 70, 80 is controlled to be equal to or greater than a threshold value. When the outputs of the second tactile sensors 61B, 71B, 81B of the fingers 60, 70, 80 are equal to or more than the threshold value, it is determined that the grip target is gripped.

As described above, in the operation of approaching the environment surface and the operation of approaching the gripping target object, in order to avoid contact with the gripping target object with an excessive force, the contact force of the fingertip portions 61, 71, 81 with respect to the environment surface is set. In order to reduce the size, feedback control is performed so that the sensor output of the first tactile sensor 61A, 71A, 81A becomes a threshold value.

Finally, the entire robot hand 10 is controlled to move the grasped grasped object to the target position (step S4).

[2-3-1. Actions that approach the environment]
Referring to FIG. 11, the operation of approaching the environmental aspect of S2 of FIG. 10 will be described in detail. FIG. 11 is a flow chart for explaining the detailed contents of the operation for approaching the environment in S2 of FIG.

The action of approaching the environment avoids the fingertip from contacting the environment with excessive force. After the fingertips of the robot hand 1 are placed in the initial posture toward the environment surface, the entire robot hand 1 is lowered to bring the three fingers 60, 70, 80 into contact with the environment surface.

The environment surface may be a horizontal flat surface, an inclined surface, an uneven surface and a non-planar surface. In the present embodiment, the fingers 60, 70 at the time of contact are contacted so that the fingers 60, 70, 80 come into contact with each other with a predetermined contact force even when the environment surface is inclined or uneven and not flat. , 80 are adjusted individually so that the contact forces of 80 are uniform. That is, the contact force of each of the fingers 60, 70, 80 that come into contact with the environment surface during the approaching operation to the environment surface is controlled to be maintained at a constant value.

At the time of approaching to the environment, the current value Iall flowing through the first tactile sensors 61A, 71A, 81A and the preset threshold value are always set for each finger 60, 70, 80 according to the force (contact force) applied to the fingertip. The difference Iall-Iref of the current value Iref is calculated.

The robot hand 10 is lowered in the initial posture so that the current value Iall of the first tactile sensors 61A, 71A, 81A becomes the threshold current value Iref, that is, the fingertip portions 61 of the fingers 60, 70, 80. , 71, 81 are feedback-controlled so that the contact force of each of the joint angles (θ1, θ2) becomes a predetermined value.

Specifically, the control unit 50 determines the target joint angles (θ1, θ2) based on the current value Iall of the first tactile sensors 61A, 71A, 81A, and the first joint units 64, 74, respectively. , 84 and the second joints 65, 75, 85, the angular velocity and torque are calculated in order to make the determined joint angles, and the command values are calculated by the servomotors 64M, 74M, 84M and 65M of the joints. , 75M, 85M to adjust the joint angle.

Here, when there is no error in the initial posture position or when the environment surface is a horizontal and flat surface, the fingertip portions 61, 71, 81 of all the fingers 60, 70, 80 contact the environment surface at substantially the same time. If there is an error in the initial posture position or if there is an inclination or unevenness on the environment surface, there may be a time difference without all fingers 60, 70, 80 contacting at the same time. If the finger that comes into contact first continues to descend, the contact force with the environmental surface becomes too large.

Therefore, in the present embodiment, while lowering the robot hand 10 until all the fingers come into contact with the environment surface, an operation of reducing the contact force of the finger that comes into contact first (joint angle θ1 is closed inside, The angle θ2 performs an operation of opening to the outside).

Specifically, for example, after the lowering operation of the robot hand 10, the current value Iall of the first tactile sensor becomes larger than the threshold current value Iref (Iall-Iref>0) (finger that comes into contact with the environment surface first). If there is, the correction amount Gang(Iall-Iref) (1) is added to the joint angles θ1 and θ2 of the finger. Here, Gang is a gain that is experimentally determined.

As a result, the joint angle θ1 is closed inward and the joint angle θ2 is opened outward, so that the contact force of the fingertip on the environmental surface is reduced. Since the same correction amount is applied in the opposite direction to each joint angle θ1 and θ2, the contact point between the finger and the environment surface does not change, that is, the posture of the fingertip can be maintained, and the contact force of the finger can be maintained. Can be maintained near a predetermined value.

When all the fingers 60, 70, 80 come into contact and the current value Iall of the first tactile sensors 61A, 71A, 81A becomes the threshold current value Iref, the operation of lowering the robot hand 10 is terminated.

Here, it is desirable that the current value Iall=threshold current value Iref, but the operation of lowering the robot hand 10 may be terminated when the current value Iall reaches the threshold value (predetermined range). For example, threshold value (predetermined range)=threshold current value Iref±A, and “0” is the most desirable and the smallest value of A is desirable.

Next, with reference to FIG. 11, an example of the operation of approaching the environmental aspect of S2 will be described. In FIG. 11, the operation of lowering the robot hand 10 is started. It is determined whether or not there is a finger whose current value of the first tactile sensor exceeds a threshold value (predetermined range) (step S11). When there is no finger whose current value of the first tactile sensor exceeds the threshold value (predetermined range) (“NO” in step S11), the process proceeds to step S13.

If there is a finger whose current value of the first tactile sensor exceeds the threshold value (predetermined range) (“Yes” in step S11), the current value of the first tactile sensor is determined to be the threshold value (predetermined range) for the finger. So as to reduce the contact force (adding the correction amount Gang(Iall-Iref) to the joint angles θ1 and θ2 to close the joint angle θ1 inside and open the joint angle θ2 outside) (step S12).

In step S13, it is determined whether or not the current values of the first tactile sensors 61A, 71A, 81A of all the fingers 60, 70, 80 have reached a threshold value (predetermined range) (step S13), and all the fingers 60, 70, When the current value of the first tactile sensors 61A, 71A, 81A of 80 reaches the threshold value (predetermined range) (“Yes” in step S13), the operation of lowering the robot hand 10 is ended.

On the other hand, when the current values of the first tactile sensors 61A, 71A, 81A of all the fingers 60, 70, 80 are not the threshold value (predetermined range) (“No” in step S13), the process returns to step S11 and all The same process is repeatedly executed until the current values of the first tactile sensors 61A, 71A, 81A of the fingers 60, 70, 80 reach the threshold value (predetermined range).

Thereby, when the environment surface is horizontal, inclined, or has unevenness, the contact force of the fingertips of all the fingers 60, 70, 80 on the environment surface can be made close to a predetermined value. ..

[2-3-2. Action to approach the grasped object]
Referring to FIG. 12, the operation of approaching the grasped object on the environmental surface in S3 will be described in detail. FIG. 12 is a flowchart for explaining the detailed contents of the operation of approaching the grip target in S3.

The operation of approaching the grasped object on the environmental surface is performed by contacting the fingertips of all fingers 60, 70, 80 of the robot hand 10 with the one finger 60 and the two fingers 70, 80 facing each other after the fingertips of the robot hands 10 contact the environmental surface. The fingers 60, 70, 80 are moved at a constant speed in the horizontal direction so as to trace the environment surface (close the fingers) in the direction in which the inter-distance is reduced (the direction in which the object to be grasped is sandwiched). The movement here is an operation of moving the object to be grasped by closing each of the fingers 60, 70, 80 so that the contact force with the environment surface does not change.

By the operation of approaching the gripping target object, the gripping target object is moved to a position where it can be gripped, or a plurality of gripping target objects are gathered in a lump. Here, when the object to be grasped is a large object or a hard object, it can be grasped without contacting the finger with the environmental surface, but when the object to be grasped is small or soft, the finger is regarded as the environmental surface. It is difficult to perform the same operation without contact. On the other hand, when the fingertip and the environment surface are in strong contact with each other, a large reaction force or frictional force is generated, so that a smooth motion cannot be performed.

Therefore, in the present embodiment, when the fingers 60, 70, 80 are moved on the environment surface, the contact force on the environment surface is controlled to be a predetermined value. Similar to the approach operation on the environment, the current value Iall of the first tactile sensors 61A, 71A, 81A of the fingers 60, 70, 80 is constantly detected, and the difference Iall-Iref from the threshold current value Iref is detected. Each is calculated.

First, the initial posture in this operation is a state in which the fingertips of the fingers 60, 70, 80 are in contact with the environmental surface, and from this state, the initial trajectory of the horizontal movement of the fingertips of the fingers 60, 70, 80 is set. Start moving at a constant speed as the target trajectory. At this time, if the environment surface is uneven or if the operation of the robot hand 10 is misaligned, the contact force changes, so the vertical component of the target trajectory of each fingertip (vertical downward direction is normal). Is corrected by a correction amount Ghei (Iall-Iref) to change the vertical component, and the joint angles θ1 and θ2 are changed so as to satisfy this change.

Specifically, for each of the fingers 60, 70, 80, when the current value Iall of the first tactile sensor is larger than the threshold current value Iref (Iall-Iref>0), the vertical component of the target trajectory of the fingertip is corrected. The correction is made with the amount Ghei(Iall-Iref) to reduce the vertical component, and θ1 and θ2 are changed so as to satisfy this. This action weakens the contact force of the fingertip. On the other hand, when the current value Iall of the first tactile sensor is less than the threshold current value Iref (Iall-Iref<0), the vertical component of the target trajectory of the fingertip is corrected by the correction amount Ghei(Iall-Iref), The vertical component is increased, and the joint angles θ1 and θ2 are changed so as to satisfy this. This action increases the contact force of the fingertip.

As described above, while adjusting the contact force so as to be within a certain range, it is possible to scrape the gripping target object or narrow the distance between the fingertips of the opposing fingers to grip the gripping target object.

Next, with reference to FIG. 12, an example of the operation of approaching the grasped object in S3 will be described. In FIG. 12, the operation of approaching the grasped object is started. First, it is determined whether or not there is a finger having a current value of the first tactile sensor≠a threshold value (predetermined range) (step S21), and a finger having a current value of the first tactile sensor≠a threshold value (predetermined range) is determined. If not (“No” in step S21), the process proceeds to step S25.

When there is a finger with which the current value of the first tactile sensor is not equal to the threshold value (predetermined range) (“Yes” in step S21), the current value of the first tactile sensor is greater than the threshold value (predetermined range) for the finger. It is determined whether or not (step S22).

When the current value of the first tactile sensor>the threshold value (predetermined range) (“Yes” in step S22), the current value of the first tactile sensor=threshold value (predetermined range) for the finger. , An operation of reducing the contact force of the fingertip on the environmental surface is performed (step S23). Specifically, the vertical component of the target trajectory of the fingertip is corrected by the correction amount Ghei(Iall-Iref) to reduce the vertical component, and the joint angles θ1 and θ2 are changed so as to satisfy this.

When the current value of the first tactile sensor>the threshold value (predetermined range) is not satisfied (“No” in step S22), that is, when the current value of the first tactile sensor<threshold value (predetermined range), the environmental surface of the fingertip An operation of increasing the contact force with respect to is performed (step S24). Specifically, the vertical component of the target trajectory of the fingertip is corrected by the correction amount Ghei (Iall-Iref) to increase the vertical component, and the joint angles θ1 and θ2 are changed so as to satisfy this.

In step S25, it is determined whether or not the current value of the second tactile sensors 61B, 71B, 81B of all the fingers 60, 70, 80 is equal to or more than the threshold value, and the second tactile sensor 61B of all the fingers 60, 70, 80 is determined. , 71B, 81B when the current value≧the threshold value (“Yes” in step S25), it is determined that the gripping target object is gripped, and the operation of approaching the gripping target object ends.

On the other hand, if the current values of the second tactile sensors 61B, 71B, 81B of all the fingers 60, 70, 80 ≧threshold value (predetermined range) (“No” in step S25), the process returns to step S21 and the second The same processing (steps S21 to S25) is repeatedly executed until the current value of the tactile sensors 61B, 71B, 81B becomes equal to or more than the threshold value.

[2-3-3. Modification]
The above control algorithm is a basic control algorithm, and various modifications are possible.

For example, the robot hand 1 has three fingers, but the present invention is not limited to this, and at least two fingers that face each other may be used, and four or more fingers may be used.

In addition, in the operation of approaching the environment and the operation of approaching the grasped object, the first tactile sensor of each finger is basically used, but depending on the shape and size of the grasped object, the timing (time) may be changed. These operations may be performed only by the second tactile sensor at the break.

Further, in the operation of approaching the grasped object, the contact with the grasped object is detected at the moment when the output value of the second tactile sensor changes from 0 to 0 or more, or the second tactile sensor of each finger detects The degree of inclination of the object may be detected from the difference in the output value. Further, the joint angle of each finger is controlled so that the output value of the second tactile sensor of all fingers becomes equal to or more than the threshold value, and when the output value of the second tactile sensor of all fingers becomes equal to or more than the threshold value, grasping is performed. The object may be moved to the target position.

Further, in the operation of approaching the object to be grasped, the number of fingers to be moved may be at least one, and when the output value of the second tactile sensor of at least one finger is equal to or more than the threshold value, grasping is performed. You may decide to detect. For example, when gripping a stick wrapping product as a model, the stick wrapping product is scraped while the two-finger side is along the environmental surface first, and the opposite one-finger side is the last one without lining the environmental surface It is also possible to perform an operation such as sticking the stick packaged item on the belly on the two-finger side.

[2-4. Example of gripping target]
13-A and 13-B are diagrams for explaining an example of the grasped object of the present embodiment. By using the control algorithm of the present embodiment, it is possible to grip a single object or plural objects such as various small objects (including thin objects) and soft objects with one gripping operation. In the example shown in FIGS. 13-A and 13-B, the robot hand 10 according to the present embodiment uses the small bottle, the small bag, the plurality of small boxes, the plastic bottle, the triangular pack, the container, the PET bottle, and the food itself (fried chicken, It indicates that a fly etc.) can be gripped.

With the robot hand 10 of the present embodiment, when gripping a small object (including an object having a small thickness) or a soft object, the robot hand 10 can be gripped by the operation of approaching the environmental surface and the operation of approaching the object to be gripped. Is. Further, when gripping a large object (including a thick object), it is possible to grip the object to be grasped without performing a motion of tracing the environment surface with a fingertip (only the finger pad). Can be gripped with).

As described above, according to the sensor mechanism for the robot hand of the present embodiment, the contact force with respect to the fingertip 61 and the environment surface on which the object to be grasped is placed is arranged on the back surface of the fingertip 61. Since the first tactile sensor 61A for detecting and the second tactile sensor 61B for detecting the contact force with respect to the grasped object are provided on the ventral side surface of the fingertip portion, It is possible to detect the contact force between the environment surface and the grasped object.

DESCRIPTION OF SYMBOLS 1 Robot hand 2 Finger tip part 3 Environmental surface 10 Robot hand 20 Arm part 21-26 Joint part 21M-26M Servo motor 30 Hand part 40 Base part 50 Control part 51,52 Motor driver 60,70,80 Finger 61,71,81 Fingertip portion 61A, 71A, 81A First tactile sensor 61B, 71B, 81B Second tactile sensor 62, 72, 82 Intermediate portion 63, 73, 83 Root portion 64, 74, 84 First joint portion
64M, 74M, 84M servo motor
65,75,85 2nd joint part 65M, 75M, 85M servo motor

Claims (6)

A sensor mechanism for a robot hand,
Fingertips,
A first tactile sensor arranged on the back surface of the fingertip portion for detecting a contact force with respect to an environment surface on which a gripping target is placed;
A second tactile sensor arranged on the ventral surface of the fingertip portion for detecting a contact force with respect to the grasped object;
A sensor mechanism for a robot hand, comprising: The robot hand according to claim 1, wherein the fingertip has a step formed on the back side and the abdomen side, and the back side is formed higher than the abdomen side. Sensor mechanism. The sensor mechanism for a robot hand according to claim 2, wherein the step of the fingertip portion is formed in a bifurcated shape. The sensor mechanism for a robot hand according to any one of claims 1 to 3, wherein the fingertip portion has a curved shape in a side view. The sensor mechanism for a robot hand according to claim 1, wherein the first and second tactile sensors have a pressure-sensitive portion formed in a sheet shape. The first and second tactile sensors are resistance type, piezoelectric type, magnetic type, capacitance type, strain gauge type, ultrasonic type, atmospheric pressure type, hydraulic type, charge type, crystal oscillator type, or optical type. The sensor mechanism for a robot hand according to any one of claims 1 to 5, wherein: