WO2019065427A1

WO2019065427A1 - Method for controlling robot hand system and robot hand system

Info

Publication number: WO2019065427A1
Application number: PCT/JP2018/034708
Authority: WO
Inventors: 佐藤　寛之
Original assignee: 倉敷紡績株式会社
Priority date: 2017-09-26
Filing date: 2018-09-20
Publication date: 2019-04-04
Also published as: JPWO2019065427A1

Abstract

[Problem] To provide a method for controlling a robot hand system and a robot hand system, whereby a target object which is difficult for a visual sensor to recognize and has a shape or size that is not fixed can be gripped. [Solution] This method for controlling a robot hand system 10 comprises: a step for detecting the position of a target object by making planar sensors 30, 50 approach toward the target object or pressing the planar sensors 30, 50; and a step for gripping the target object on the basis of positional information about the detected target object by narrowing the gap between a pair of gripping surfaces 27, 47 while maintaining the pair of gripping surfaces approximately parallel to each other.

Description

Robot hand system control method and robot hand system

The present invention relates to a robot hand attached to and used at the tip of a robot arm.

In order to expand the application range of industrial robots, development of robot hands capable of holding objects of various shapes or sizes is in progress.

For example, Patent Document 1 includes a pair of slide portions sliding along a linear axis, and a grip portion fixed to each of the slide portions and having a gripping claw at a tip end portion, and the grip portion is the linear axis A hand is described that includes an articulation that rotates about an axis of rotation that is orthogonal to a plane that includes the tip of the gripping claw and the tip of the gripping claw. Then, it is described that workpieces of different sizes and shapes can be reliably gripped by gripping workpieces by bringing gripping claws facing substantially in parallel to approach each other.

JP 2012-176461 A Japanese Patent Application Laid-Open No. 05-337864

By the way, when the robot handles an object whose position and shape are not constant, generally, the object is recognized by a visual sensor such as a stereo camera, and the arm / hand is operated based on the position information and the like. According to the robot hand described in Patent Document 1, it is possible to grip an object whose shape or size is not constant, but even in that case, it is necessary to obtain in advance the approximate position of the object to be gripped.

However, depending on the type of object, it may be difficult to obtain position information by the visual sensor. For example, in order to obtain position information with a stereo camera, it is necessary to find corresponding points on each image, but it is difficult to extract feature points to be corresponding points for an object with complicated shape and monotonous color . Examples of such objects are foods such as hamburger and fried chicken. In addition, when such objects are piled up, recognition by the visual sensor becomes more difficult.

As an example of recognizing an object using a sensor other than a visual sensor, Patent Document 2 discloses that the work object is provided by a force sensor provided at the tip of the hand while the hand moves along the surface of the work object. A method is described for detecting the position of a hole in a surface. Thus, it is possible to detect the position of the hole of the work object even when the relative position and the relative posture between the robot and the work object are incorrect.

However, in Patent Document 2, although the relative position of the work object is unknown, the shape of the work object and the arrangement of the holes are known. The method described in Patent Document 2 can not be applied to an object whose shape or size is not constant.

The present invention has been made in consideration of the above, and it is an object of the present invention to provide a robot hand system and a robot hand system control method capable of gripping an object whose shape or size is not constant without relying on a visual sensor. I assume.

In the robot hand system control method of the present invention, a pair of sensors is detected based on the step of detecting the position of the target by bringing a planar sensor close to or against the target and detecting the position information of the target detected. And holding the object while narrowing the distance between the pair of holding surfaces while keeping the holding surface at a predetermined angle.

According to this method, the approximate position of the object is detected by the search unit, and the distance between the two is kept narrow while keeping the first grip surface and the second grip surface substantially parallel. And / or can hold an object whose size is not constant.

The robot hand system according to the present invention has a first finger, a second finger, and a searching unit, and the first finger is a first joint and a second joint that perform rotational motion, and the first finger. And a second gripping portion provided at the distal end portion of the second finger portion, and the second finger portion is provided at the distal end portion of the second finger portion with a third joint and a fourth joint performing rotational motion. And a gripping surface. The rotation axes of the first to fourth joints are parallel to each other, and the first gripping surface and the second gripping surface are disposed so as to be directly opposite each other by the rotational motion of the first to fourth joints, The spacing can be increased or decreased while maintaining the angle of. The search unit is formed of a planar tactile sensor or a proximity sensor, and detects the position of the object to be grasped.

With this configuration, the approximate position of the object is detected by the search unit, and the distance between the two is kept narrow while keeping the first grip surface and the second grip surface substantially parallel. And / or can hold an object whose size is not constant.

Preferably, maintaining the first gripping surface and the second gripping surface at the predetermined angle maintains the first gripping surface and the second gripping surface substantially in parallel. The angle formed by the first gripping surface and the second gripping surface can be determined according to the shape of the object, but by keeping the first gripping surface and the second gripping surface substantially parallel, it is possible to select objects of various shapes. It becomes easy to grip the object.

Preferably, the first gripping surface and the second gripping surface are flat. Thereby, even when the shapes of the individual objects differ significantly, the object can be stably gripped. The gripping surface may not be a completely flat surface. For example, the surface may be provided with an uneven surface with non-slip, etc., and a flat surface may be formed as an overall shape.

Preferably, the search unit is configured of a first tactile sensor provided on the first holding surface and a second tactile sensor provided on the second holding surface. As described above, when the search unit is incorporated into part of the robot hand, the configuration of the entire system can be simplified, and there is an advantage that the movement amount of the robot hand when searching for and gripping an object decreases.

Alternatively, the search unit may be provided separately from the robot hand main body including the first finger and the second finger.

Preferably, the first joint is torque-controlled, and at least the second joint follows the movement of the first joint to maintain the first gripping surface and the second gripping surface at the predetermined angle. Position control. As a result, since the first joint maintains a constant torque after gripping the object, the gripping state of the object is maintained. At this time, since the gripping force is determined by the torque of the first joint, by setting an appropriate torque according to the object to the first joint, the object is broken even if the object which is flexible and easily deformed is gripped I have not. As described above, by combining the torque control and the position control to control each joint in an interlocked manner, it is possible to stably grip the flexible flexible material.

According to the robot hand system control method or robot hand system of the present invention, even if the object is difficult to be recognized by the visual sensor, the approximate position can be detected by the search unit, and the first grip surface and the second grip surface are approximately Since holding is performed in close proximity while keeping parallel, it is possible to hold an object whose shape and / or size is not constant. As described above, the robot hand system control method and robot hand system according to the present invention are suitable for grasping an object whose shape and size are not constant and which are difficult to be recognized by a visual sensor.

It is a figure showing the structure of the robot hand system of one embodiment of the present invention. It is a figure explaining the holding | grip operation | movement of the robot hand system of one Embodiment of this invention. It is a figure explaining the operation at the time of grasping a plurality of subjects. It is a tactile image which a tactile sensor acquires in the state of FIG. 3A. It is a figure which shows the structure of the robot hand system of other embodiment of this invention. It is a figure explaining the number of joints, and the relation of grasping position.

A first embodiment of a robot hand according to the present invention will be described based on FIGS. 1 to 4.

In FIG. 1, a robot hand system 10 according to this embodiment includes a robot hand 11, and a search unit 15 is incorporated in the robot hand 11. The robot hand 11 has a base 12, a first finger 21, and a second finger 41. The robot hand 11 is used by attaching the base 12 to the tip of the robot arm 90.

The first finger 21 has a proximal end side of the link 22 fixed to the base 12 (fixed end 28), and a first joint 23 connecting the link 22 and the link 24, and a second joint 25 connecting the link 24 and the link 26. The first holding surface 27 is provided at the tip end portion 29.

The first joint 23 rotationally moves about an axis of rotation perpendicular to the connecting

links

22 and 24 so as to increase or decrease the link angle θ 1 between the

links

22 and 24. Similarly, the second joint 25 rotationally moves about an axis of rotation perpendicular to the linking

links

24 and 26 so as to increase or decrease the link angle θ 2 between the

links

24 and 26.

The first joint 23 and the second joint 25 are preferably driven by independent actuators (not shown). The actuator is a rotary actuator, preferably a servomotor. This is because position control and torque control to be described later can be easily realized. Also, the servomotor is preferably provided in the vicinity of the driven first joint or second joint. This is because the transfer mechanism can be omitted and the structure of the robot hand 11 can be simplified.

Preferably, the first joint 23 is position controllable and torque controllable, and the second joint 25 is position controllable. The torque control is control for rotating a joint or maintaining a constant torque for rotating the joint. Specifically, since the torque of the motor is correlated with the current, the current supplied to the motor is controlled to be constant. Position control is control to make the rotational position (angle) of a joint constant, and after the joint reaches a target position, the position is maintained. When using a servomotor, a mechanism for normal position control is incorporated as a function of the motor.

A first tactile sensor 30 is provided on the surface of the first grip surface 27. The first tactile sensor is a planar sensor in which elements for acquiring pressure and displacement are arranged in a matrix. The first tactile sensor detects the pressure acting on the first grip surface when the robot hand 11 grips the object, and acquires the distribution as a tactile image. The type of the first tactile sensor is not particularly limited, and various known sensors such as a conductive rubber type, a conductive paint type, and an optical waveguide type can be used. The first tactile sensor is preferably provided on the entire surface of the first gripping surface.

The second finger 41 has the same structure as the first finger 21. The second finger 41 has a proximal end side of the link 42 fixed to the base 12 (fixed end 48), a third joint 43 connecting the link 42 and the link 44, and a fourth joint 45 connecting the link 44 and the link 46 The second grip surface 47 is provided at the tip end portion 49. The third joint and the fourth joint rotate to increase or decrease the angles θ3 and θ4 between the adjacent links. The third joint and the fourth joint are each driven by an independent actuator (not shown), and the actuator is a rotary actuator, preferably a servomotor. The third joint and the fourth joint are position controllable. A second tactile sensor 50 is provided on the surface of the second grip surface 47. The second tactile sensor is preferably provided on the entire surface of the second gripping surface.

The first gripping surface 27 and the second gripping surface 47 grip the object by sandwiching the object therebetween. The first and second gripping surfaces are preferably planar. This is because it is easy to hold an object of various shapes. Further, the first grip surface and the second grip surface are provided so as to be able to face each other by the pivoting motion of the first to fourth joints. In the present embodiment, the first gripping surface is achieved because the first finger 21 and the second finger 41 are on the same plane, and the rotation axes of the first to fourth joints are perpendicular to the plane and all are parallel. And the second gripping surface can be made to face each other. In addition, by appropriately operating the first to fourth joints, the distance between the first gripping surface and the second gripping surface is changed, for example, while facing each other substantially in parallel while facing each other at a predetermined angle. It is possible.

The search unit 15 of the present embodiment is constituted by the first tactile sensor 30 and the second tactile sensor 50, and searches for the position of the object using these sensors. Preferably, the first gripping surface 27 and the second gripping surface 47 open at 180 degrees to constitute one plane (see FIG. 2A described later). The search unit 15 may be configured of only one of the first tactile sensor and the second tactile sensor. Moreover, the sensor which comprises a search part is not restricted to a tactile sense sensor, You may be planar proximity sensors, such as an electrostatic capacitance type.

Next, the operation of the robot hand 11 of this embodiment will be described. Here, a method will be described in which the first joint is subjected to torque control, and the second to fourth joints are controlled in position following the movement of the first joint to pick up an object from the piled state.

Referring to FIG. 2A, first, the first tactile sensor 30 and the second tactile sensor 50 are opened at 180 degrees, and the search unit 15 formed of the first and second tactile sensors is pressed against the mountain of the object and held. Get the approximate position of the target object. At this time, it is preferable to feed back the pressure of the sensor so that the search unit is not pressed against the object too much. Also, preferably, the sensor surface of the search unit is leveled and pressed from above. This is to detect the object more reliably. The search operation may be performed multiple times while shifting the position of the robot hand 11 little by little.

Referring to FIG. 2B, the first gripping surface 27 and the second gripping surface 47 are opened approximately a little wider than the width of the object while keeping substantially parallel. The robot arm 90 is operated to move the robot hand 11 close to the object, and the robot hand is advanced so that the object W enters between the first gripping surface 27 and the second gripping surface 37. During this time, the required angles of the first joint 23, the second joint 25, the third joint 43 and the fourth joint 45 are calculated by the control unit (not shown), and the first joint 23, the second joint 25, the third joint 43 and the third The four joints 45 are all position controlled by the control unit to take a required angle.

Referring to FIG. 2C, the first joint 23 is approached while maintaining the first gripping surface 27 and the second gripping surface 47 substantially parallel. Specifically, the first joint 23 is rotated by torque control in a direction in which the distance between both gripping surfaces is narrowed, the angle of the first joint is detected by an encoder or the like incorporated in the servomotor, and both gripping surfaces are The control unit calculates the target positions of the second joint 25, the third joint 43 and the fourth joint 45 for keeping parallel, and controls the positions of the second to fourth joints at the target positions.

Referring to FIG. 2D, when the object W is gripped by the first gripping surface 27 and the second gripping surface 47, the rotation of the first joint is stopped when the torque and the reaction force of the first joint 23 are balanced. , The second joint 25 following the first joint, the third joint 43 and the fourth joint 45 are also stopped. After that, since the first joint is subjected to torque control, the object is held at a constant torque. However, if the reaction force decreases for some reason, the first joint rotates further in the direction to narrow the distance between the two

gripping surfaces

27 and 47, and if the reaction force increases, the first joint receives both gripping

surfaces

27 and 47. Set back in the direction to widen the gap.

As described above, the robot hand system 10 according to the present embodiment includes the robot hand 11, and the approximate position of the object is detected by the search unit 15 incorporated in the robot hand 11, and the first gripping surface 27 and the second gripping surface While keeping 47 substantially parallel, the distance between the two gripping surfaces is narrowed to grip the object.

Also, by controlling the torque of the first joint 23 and causing the second joint 25, the third joint 43 and the fourth joint 45 to follow the movement of the first joint, the first joint becomes constant after gripping the object. The torque is maintained to hold the object. At this time, since the gripping force is determined by the torque of the first joint, setting the appropriate torque according to the object to the first joint will damage the object even if it is gripping a flexible and easily deformable object. I have not. The same effect can be obtained even if the third joint and the fourth joint are fixed by position control, the first joint is subjected to torque control, and only the second joint follows the movement of the first joint.

When the

tactile sensors

30 and 50 are provided on the first and second

gripping surfaces

27 and 47 as in the present embodiment, it is possible to cope with the case where a plurality of objects are gripped. It will be described below.

When the first gripping surface 27 and the second gripping surface 47 grip the object, a tactile image is obtained by the first tactile sensor 30 and the second tactile sensor 50 provided on the surfaces of both gripping surfaces. When a plurality of objects W1 and W2 are gripped as shown in FIG. 3A, the island appears to be split into a plurality on the tactile image. FIG. 4 shows an example of a tactile image by the first tactile sensor (left side in FIG. 4) and a tactile image by the second tactile sensor (right side in FIG. 4).

Next, the tactile image is read into a calculation unit (not shown), and the number of objects held is determined from the number and shape of islands of the tactile image. A well-known method can be used for the image analysis by a calculating part. For example, it is possible to binarize the tactile image as a gray-scale image while gradually increasing the threshold and count the number of islands that have appeared. Further, if the positions of the centers of gravity of the islands of the tactile image by the first tactile sensor and the tactile image from the second tactile sensor substantially correspond to each other, it can be determined that the islands are due to the same object.

When it is determined by the computing unit that a plurality of objects are gripped, the angle formed by the first gripping surface 27 and the second gripping surface 47 is changed from parallel with reference to FIG. 3B. In this embodiment, the angle is changed so that both gripping surfaces are in a wedge shape as viewed from the side (the front or the back of FIG. 3B). In order to change the angle formed by the two gripping surfaces, for example, in FIG. 3B, the first joint 23 is rotated by torque control in the direction in which the distance between the two gripping surfaces is narrowed, so that both gripping surfaces form a predetermined angle. The control unit may calculate the target positions of the 2-joint 25, the third joint 43 and the fourth joint 45, and control the positions of the second to fourth joints to the target position. As a result, it is possible to hold only one object W1 and release the extra object W2. If it is difficult to determine the number of objects held, the distance between the first and second holding surfaces can be increased to release all the objects.

As described above, in the robot hand 11 according to the present embodiment, when a plurality of objects are gripped, the angle formed by the two gripping surfaces is changed to release the extra objects.

The present invention is not limited to the embodiments described above, and modifications are possible within the scope of the technical idea thereof.

For example, the search unit may be provided separately from the robot hand main body. The robot system 60 shown in FIG. 5 includes a robot hand main body 19 and a search unit 17 provided separately. The search unit 17 is configured by a planar tactile sensor or proximity sensor, and is controlled by the link structure 16 separately from the robot hand body.

Also, for example, in each of the above-described embodiments, the number of joints possessed by each finger is two, but the first finger 21 and / or the second finger 41 may be moved to the first to fourth joints by position control. It may further have joints performing rotational movement about parallel rotation axes. Referring to FIG. 6A, when the number of joints in each finger is two, the first gripping surface 27 and the second gripping surface 47 can face each other at only one point. On the other hand, referring to FIG. 6B, when a joint 54 is added to one finger, both gripping surfaces can face and contact within a certain region extending in the substantially Y direction. Further, referring to FIG. 6C, adding

joints

34, 54 to both fingers allows both gripping surfaces to face and contact within a region extending in the X and Y directions.

10, 60

Robot Hand System

11, 19 Robot Hand (Robot Hand Body)
12 base 15 search unit 16 link structure 17 search unit 21

first finger

22, 24 and 26 link 23 first joint 25 second joint 27 first grasping surface 28 fixed end 29 tip 30 first tactile sensor 34 joint 41 first joint 2

fingers

42, 44, 46 link 43 third joint 45 fourth joint 47 second gripping surface 48 fixed end 49 tip 50 second tactile sensor 54 joint 90 robot arm W, W1, W2 target object θ1, θ2, θ3 , Θ4 link angle

Claims

Moving or pressing a planar sensor on an object to detect the position of the object;
Grasping the object by narrowing the distance between the pair of gripping surfaces while keeping the pair of gripping surfaces at a predetermined angle based on the detected position information of the object;
A robot hand system control method comprising:
It has a first finger, a second finger, and a search unit,
The first finger has a first joint and a second joint that perform rotational movement, and a first gripping surface provided at the tip of the first finger.
The second finger has a third joint and a fourth joint that perform rotational movement, and a second gripping surface provided at the tip of the second finger.
The rotation axes of the first to fourth joints are parallel to each other,
The first gripping surface and the second gripping surface are disposed to be able to face each other by rotational movement of the first to fourth joints, and can increase or decrease the spacing while maintaining a predetermined angle,
The search unit includes a planar tactile sensor or a proximity sensor, and detects the position of the object to be grasped.
Robot hand system.
Maintaining the first gripping surface and the second gripping surface at the predetermined angle is maintaining the first gripping surface and the second gripping surface substantially parallel.
The robot hand system according to claim 2.
The first gripping surface and the second gripping surface are planar,
The robot hand system according to claim 2 or 3.
The search unit includes a first tactile sensor provided on the first grip surface and a second tactile sensor provided on the second grip surface.
The robot hand system according to any one of claims 2 to 4.
The search unit is provided separately from the robot hand main body including the first finger and the second finger.
The robot hand system according to any one of claims 2 to 4.
Position control such that the first joint is torque-controlled, and at least the second joint follows the movement of the first joint to maintain the first gripping surface and the second gripping surface at the predetermined angle To be
A robot hand system according to any one of claims 2 to 6.