JP4888375B2 - Robot hand - Google Patents

Description

  The present invention relates to a robot hand, and more particularly to a multi-finger hand that holds an object.

In order to grip and lift an object with a robot hand, a gripping force is required, but a gripping force corresponding to the weight of the object to be gripped is required. If an object is gripped with a gripping force more than necessary, the object may be destroyed or deformed. Therefore, it is desired to determine a gripping force suitable for the object to be gripped.
Patent Document 1 discloses a method of calculating the weight of an object from the drive current of the servo motor by moving the arm with a servo motor while the object is attached to the tip of the arm of the articulated robot.

JP 2004-25387 A

However, although the robot of Patent Document 1 can detect the weight of an object, there is a problem that an appropriate gripping force cannot be determined for each object having various weights.
The present invention has been made to solve such problems, and an object thereof is to provide a robot hand capable of determining a gripping force suitable for an object to be gripped.

The robot hand according to the present invention includes at least two gripping members, an actuator for moving each gripping member, a load detection means for detecting a load acting on at least one gripping member, and at least two gripping by driving the actuator. Grip the side of the object with a member, drive the actuator, grasp the object with at least two gripping members and lift it, gradually reduce the gripping force to pinch the object with these gripping members, and detect the load And a control unit that determines a gripping force when a load acting in a direction along the surface of the object detected by the means falls as a gripping force necessary for lifting the object.

The actuator is composed of an ultrasonic actuator that uses a piezoelectric element as a vibrating body, and the load detection means is formed by the piezoelectric element of the ultrasonic actuator, and is configured to detect a load using the inverse piezoelectric effect generated in the piezoelectric element. can do.
Further, the control unit detects the weight of the object based on the gripping force of the object by the at least two gripping members and the load acting in the direction along the surface of the object detected by the load detection unit, It is also possible to detect a coefficient of friction between at least two gripping members that grip the object and the surface of the object.
As the actuator, a multi-degree-of-freedom actuator having two or more degrees of freedom that can move in at least two directions, that is, a direction in which the gripping member grips the object and a direction in which the gripping member slides on the object can be used.
The gripping member may be composed of a finger part, and may be provided with at least two actuators arranged corresponding to each finger part and moving the corresponding finger parts.

  According to this invention, the state is changed between a state in which the gripping member slides with respect to the surface of the object and a state in which the gripping member moves the object while changing the gripping force of the object by the at least two gripping members. Thus, it is possible to determine a gripping force suitable for the object to be gripped.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1
FIG. 1 shows the configuration of a robot hand according to Embodiment 1 of the present invention. Each robot hand has at least two finger parts A driven by an ultrasonic actuator, and the control unit 1 is connected to the ultrasonic actuator of each finger part A.
As shown in FIG. 2, each finger A of the robot hand has a first node C1, a second node C2, and a third node C3 that are sequentially connected to each other. The first node C1 has a vibrating body 2 and a rotor 3 that constitute a first ultrasonic actuator U1 for moving the second node C2 relative to the first node C1. The second node C2 is fixed. Similarly, the second node C2 includes a vibrating body 4 and a rotor 5 that constitute a second ultrasonic actuator U2 for moving the third node C3 relative to the second node C2, and the rotation The third node C3 is fixed to the child 5.
The vibrator 2 of the first ultrasonic actuator U1 and the vibrator 4 of the second ultrasonic actuator U2 are connected to the control unit 1 respectively.

Here, FIG. 3 shows the structure of the first ultrasonic actuator U1. The vibrating body 2 is sandwiched between the base portion 11 and the stator 12, and the base portion 11 and the stator 12 are connected to each other via a connecting bolt 13 passed through the vibrating body 2. A concave portion 14 is formed on the stator 12 on the side opposite to the surface in contact with the vibrating body 2, and the lower portion of the substantially spherical rotor 3 is accommodated in the concave portion 14.
For convenience of explanation, the Z axis extends from the base 11 toward the rotor 3, the X axis extends in a direction perpendicular to the Z axis, and the Y axis extends in a direction perpendicular to the Z axis and the X axis. And

  An annular step 15 located on the XY plane is formed in the recess 14 of the stator 12, and the rotor 3 is rotatably supported in contact with the step 15 of the recess 14. The second node C2 is fixed to the rotor 3, and the rotor 3 is pressed against the step 15 of the stator 12 by the holding member 16 that connects the outer periphery of the second node C2 and the stator 12. Yes.

  The vibrating body 2 includes flat plate-like first to third piezoelectric element portions 21 to 23 that are positioned on the XY plane and overlapped with each other, and the first to third piezoelectric element portions 21 to 21 are overlapped with each other. 23 is electrically connected to the control unit 1.

  Specifically, as shown in FIG. 4, the first piezoelectric element portion 21 includes an electrode plate 21a, a piezoelectric element plate 21b, an electrode plate 21c, a piezoelectric element plate 21d, and an electrode plate 21e each having a disk shape. It has a structure that is sequentially stacked. Similarly, the second piezoelectric element portion 22 has a structure in which an electrode plate 22a, a piezoelectric element plate 22b, an electrode plate 22c, a piezoelectric element plate 22d, and an electrode plate 22e each having a disk shape are sequentially stacked. 3 has a structure in which an electrode plate 23a, a piezoelectric element plate 23b, an electrode plate 23c, a piezoelectric element plate 23d, and an electrode plate 23e each having a disk shape are sequentially stacked. These piezoelectric element portions 21 to 23 are arranged in a state of being insulated from the stator 12 and the base portion 11 through insulating sheets 24 to 27 and from each other.

As shown in FIG. 5, the pair of piezoelectric element plates 21 b and 21 d of the first piezoelectric element portion 21 has portions that are divided into two in the Y-axis direction and have opposite polarities, and each has a Z-axis direction (thickness direction ), The piezoelectric element plate 21b and the piezoelectric element plate 21d are arranged inside out.
The pair of piezoelectric element plates 22b and 22d of the second piezoelectric element portion 22 is polarized so as to be expanded or contracted in the Z-axis direction (thickness direction) as a whole without being divided into two. The element plate 22b and the piezoelectric element plate 22d are arranged inside out.
In the pair of piezoelectric element plates 23b and 23d of the third piezoelectric element portion 23, the portions divided into two in the X-axis direction have opposite polarities and are opposite to expansion and contraction in the Z-axis direction (thickness direction), respectively. The piezoelectric element plate 23b and the piezoelectric element plate 23d are disposed so as to be reversed with respect to each other.

  An electrode plate 21a and an electrode plate 21e disposed on both surface portions of the first piezoelectric element portion 21, an electrode plate 22a and an electrode plate 22e disposed on both surface portions of the second piezoelectric element portion 22, and a third The electrode plate 23a and the electrode plate 23e disposed on both surface portions of the piezoelectric element portion 23 are electrically grounded. Further, the electrode plate 21 c disposed between the pair of piezoelectric element plates 21 b and 21 d of the first piezoelectric element portion 21 and the pair of piezoelectric element plates 22 b and 22 d of the second piezoelectric element portion 22 are disposed. The electrode plate 23c disposed between the pair of piezoelectric element plates 23b and 23d of the third piezoelectric element portion 23 is electrically connected to the control portion 1 respectively.

  By applying an AC voltage having a frequency close to the natural frequency of the ultrasonic actuator U1 from the control unit 1 to at least two of the piezoelectric element units 21 to 23, the ultrasonic vibration is applied to the step 15 of the stator 12. Is generated, and the rotor 3 can be rotated in an arbitrary direction via the frictional force. As the rotor 3 rotates, the second node C2 moves.

  Further, when a stress is applied to the piezoelectric element portions 21 to 23 of the vibrating body 2 due to an external force applied to the second node C2, at least one of the piezoelectric element portions 21 to 23 according to the direction of the stress. A voltage is generated by a reverse piezoelectric effect between a pair of piezoelectric element plates constituting the. For this reason, the stress which acts on the vibrating body 2 is detectable by measuring the voltage which generate | occur | produces between a pair of piezoelectric element board of each piezoelectric element part 21-23.

The second ultrasonic actuator U2 has the same configuration as that of the first ultrasonic actuator U1, and includes a control unit in at least two piezoelectric element units among the first to third piezoelectric element units forming the vibrating body 4. By applying an AC voltage having a frequency close to the natural frequency of 1 to the ultrasonic actuator U2, the rotor 5 can be rotated in an arbitrary direction. With the rotation of the rotor 5, the third node C3 moves.
Further, by measuring the voltage generated between the pair of piezoelectric element plates of the first to third piezoelectric element portions forming the vibrating body 4, the stress acting on the vibrating body 4 can be detected.

Next, the operation of the robot hand according to the first embodiment will be described.
As shown in FIG. 1, the control unit 1 is placed on the placement surface T by moving the two finger parts A by driving the ultrasonic actuators U1 and U2 of each finger part A. The object S is held by the third node C3 of both finger parts A. However, at this time, the gripping force G is made small so that the third node C3 is in light contact with the object S.
At this time, as shown in FIG. 6, the object S receives the vertical drag N0 having the same magnitude as the gravity W from the mounting surface T, and the gravity W and the vertical drag N0 are in a balanced state. .

  In this state, the control unit 1 moves the ultrasonic actuator U1 of both fingers A so that the second node C2 moves in the horizontal direction H and inward with respect to the first node C1 of each finger A. By driving, a gradually increasing gripping force G is applied to the object S from the third node C3 of each finger A, and the ultrasonic actuator U2 of both fingers A is driven, as shown in FIG. The third node C3 is raised in the vertical direction V with respect to the second node C2 of each finger A.

When the gripping force G acting on the object S from the third node C3 of each finger A is small, the object S does not lift up, and the third node C3 of both fingers A slides on the side surface of the object S upward. It becomes. At this time, as shown in FIG. 8, a dynamic friction force is generated at the contact portion between the object S and the third node C3, and the dynamic friction force facing the upper side of the size μG with the dynamic friction coefficient being μ is represented by each finger portion A. It acts on the object S from the third section C3. For this reason, the dynamic frictional force of 2 μG is applied to the object S by both fingers A, and the sum of the dynamic frictional force 2 μG and the vertical drag N received by the object S from the placement surface T is balanced with the gravity W acting on the object S. And
N + 2 μG = W (1)
The relationship holds.
On the other hand, a load F directed downward from the object S acts on the third node C3 of each finger portion A that slides upward on the side surface of the object S. This load F has a magnitude equal to the dynamic frictional force μG acting on the object S from the third node C3 of each finger A. That is,
F = μG (2)
It becomes.

  The gripping force G can be grasped based on the drive voltage supplied from the control unit 1 to the vibrating body 2 of the first ultrasonic actuator U1 of each finger portion A. Further, the load F is obtained by measuring a voltage generated between the pair of piezoelectric element plates of the first to third piezoelectric element portions that form the vibrating body 4 of the second ultrasonic actuator U2 of each finger portion A. Can be detected.

Therefore, when the relationship between the gripping force G by the third node C3 of each finger A, the load F acting on the third node C3 of each finger A and the normal force N that the object S receives from the placement surface T is shown in a graph. As shown in FIG. When the gripping force G is gradually increased from time T0, the load F is increased in proportion thereto, and the normal drag N that the object S receives from the placement surface T gradually decreases from the initial value N0.
And the gripping force G is μG = W / 2 (3)
When the time T1 increases to a value G1 that satisfies the condition, the normal drag N received by the object S from the placement surface T becomes 0, and the slip between the third joint C3 of each finger A and the side surface of the object S is completed. Then, as shown in FIGS. 10 and 11, the object S is lifted away from the placement surface T. At this time, the load F1 acting on the third node C3 of each finger A is:
F1 = W / 2 (4)
It becomes.

Once the object S is lifted in this way, even if the gripping force G is further increased, the frictional force that acts on the object S from the third section C3 of each finger portion A remains W / 2 and does not change. The load F acting on the third node C3 of the part A is also constant with F1 = W / 2.
Therefore, the control unit 1 uses the gripping force G1 when the load F detected by the vibrating body 4 of the second ultrasonic actuator U2 of each finger A becomes a constant value F1 = W / 2, and the object S It can be determined as a gripping force required for lifting.
If the gripping force necessary for lifting the object S is determined in this way, it is possible to avoid applying an excessive gripping force to the object S and to prevent the object S from being destroyed or deformed. It becomes.

  Further, the gravity W acting on the object S, that is, the weight of the object S can be detected from the value of the load F1 by the above formula (4), and the gripping force G and the load F can be detected by the above formula (2). The dynamic friction coefficient μ between the object S and the third node C3 can be detected from the value of. For this reason, the object S can be grasped and moved by the third section C3 of the finger part A, and torque control, speed control, etc. when operating the object S can be performed with higher accuracy.

In the first embodiment, the first ultrasonic actuator U1 of each finger A is driven uniaxially in the horizontal direction H to generate the gripping force G in the third node C3 and the second ultrasonic actuator U2 is Although one axis is driven in the vertical direction V to raise the third node C3 and the load F is detected by the vibrating body 4 of the second ultrasonic actuator U2, the present invention is not limited to this.
For example, as shown in FIG. 12, the first ultrasonic actuator U1 of each finger A is driven in two axes to move the second node C2 in the horizontal direction H with respect to the first node C1, and in the vertical direction V. The third node C3 is raised while generating the gripping force G in the third node C3, and the vibrating body 4 of the second ultrasonic actuator U2 can be used exclusively for detecting the load F. .

On the other hand, the second ultrasonic actuator U2 is driven in two axes to move the third node C3 in the horizontal direction H and the vertical direction V relative to the second node C2, thereby holding the third node C3. The third node C3 may be raised while generating the force G, and the vibrator 2 of the first ultrasonic actuator U1 may be used exclusively for detecting the load F.
In addition, as shown in FIG. 13, the first joint C1 is omitted, and the finger part of one joint of only the second joint C2 and the third joint C3 is used, and the second ultrasonic actuator U2 is driven biaxially to By moving the third node C3 in the horizontal direction H and moving in the vertical direction V with respect to the second node C2, the third node C3 is raised while generating a gripping force G in the third node C3. The load F can also be detected by the vibrating body 4 of the second ultrasonic actuator U2.

Embodiment 2
FIG. 14 is a graph showing the relationship between the gripping force G by the third node C3 of each finger part A and the load F acting on the third node C3 of each finger part A in the robot hand according to the second embodiment. The robot hand according to the second embodiment has the same configuration as the robot hand according to the first embodiment, but determines an appropriate gripping force for the object S that is already gripped and lifted. It is something to try.

The control unit 1 moves the two finger parts A by driving the ultrasonic actuators U1 and U2 of each finger part A, and grips the object S with the third joint C3 of both finger parts A at time T0. lift. Note that the gripping force G0 acting on the object S from the third node C3 of each finger A is an appropriate value. At this time, since the object S has already been lifted, the load F0 acting on the third node C3 of each finger A is:
F0 = W / 2 (5)
It is.

Here, the control unit 1 drives the ultrasonic actuator U1 of both finger parts A so as to move the second node C2 outward in the horizontal direction H with respect to the first node C1 of each finger part A. Thus, the gripping force G acting on the object S from the third node C3 of each finger A is gradually reduced. However, as long as the object S is supported by the third node C3 of both finger parts A and is stationary, the load F0 acting on the third node C3 of each finger part A remains W / 2. .
As the gripping force G decreases, the coefficient of static friction between the object S and the third node C3 is set to μ ₀ and acts between the object S and the third node C3 of each finger portion A at time T2. When the maximum frictional force μ ₀ G falls below the half value W / 2 of the gravity W acting on the object S, the object S starts to slide down between the third nodes C3 of both finger portions A. The gripping force G2 at this time T2 is
μ ₀ G2 = W / 2 (6)
It is represented by

When the object S starts to slide in this manner, a dynamic friction force μG smaller than the maximum friction force μ ₀ G acts between the object S and the third node C3, and thus acts on the third node C3 of each finger A. The load F to be abruptly falls from W / 2 to F2. The load F2 at this time is
F2 = μG2 (7)
It is represented by

Therefore, the control unit 1 uses the gripping force G2 when the load F detected by the vibrating body 4 of the second ultrasonic actuator U2 of each finger A falls to the gripping force necessary for lifting the object S. Can be determined as
Thereafter, as the gripping force G is further reduced, the load F also decreases. Therefore, the gripping force G is increased again to prevent the object S from falling, and the gripping force is slightly larger than G2 or G2. It can be a value.
By determining the gripping force necessary for lifting the object S in this manner, it is possible to avoid applying an excessive gripping force to the object S and destroying or deforming the object S, as in the first embodiment. It is possible to prevent the risk of doing so.

Further, the gravity W acting on the object S, that is, the weight of the object S can be detected from the value of the load F0 by the above formula (5), and the gripping force G and the load F can be detected by the above formula (6). The coefficient of static friction μ ₀ between the object S and the third node C 3 can be detected from the value of. For this reason, the object S can be grasped and moved by the third section C3 of the finger part A, and torque control, speed control, etc. when operating the object S can be performed with higher accuracy.

  In the second embodiment, the gripping force necessary for lifting the object S can be determined simply by changing the gripping force G monotonously. Therefore, one joint as shown in FIG. The present invention can be applied to a robot hand having a uniaxially driven finger that can move only in the horizontal direction H.

Other Embodiments In the first and second embodiments described above, the object S is gripped by the two fingers A. Similarly, a multi-finger hand having three or more fingers is configured, A gripping force may be generated from each of the fingers by holding the object S with the above fingers. In this case, the resultant force of the frictional force acting between each finger part and the side surface of the object S is compared with the gravity acting on the object S.
In the first and second embodiments, the vibrating bodies 2 and 4 of the ultrasonic actuators U1 and U2 for driving each finger A are configured as load detection means for detecting the load acting on each finger A. Although the piezoelectric element plate is used, the present invention is not limited to this. A dedicated force sensor is attached to each finger A separately from the actuator that drives the finger A, and the load is detected by the force sensor. Good. However, as in the first and second embodiments, if the load is detected using the vibrators 2 and 4 of the ultrasonic actuators U1 and U2 for driving each finger A, a smaller and simpler configuration is possible. Robot hands can be realized.
The robot hands of Embodiments 1 and 2 described above can be used by being mounted on a self-propelled robot.

In Embodiments 1 and 2 described above, the gripping force G when the load acting on each finger part A becomes constant or falls is determined as the gripping force required when lifting the object S. However, the present invention is not limited to this. If a change in load that appears when the state of each finger A and the object S changes is detected, the gripping force at that time is determined as the gripping force required to lift the object S. Good. For example, in the first embodiment, when the load momentarily drops when the object S is lifted, the gripping force G at that time may be determined as a gripping force necessary for lifting the object S.
In the first and second embodiments, the load acting on the two finger portions A is detected. However, the same thing can be performed only by detecting the load acting on the one finger portion A. .
In the first and second embodiments, two actuators that are arranged corresponding to the respective finger portions and move the corresponding finger portions are provided. However, a single actuator that can move the two finger portions simultaneously is used. May be.
In the first and second embodiments, the gripping force necessary for lifting the placed object in the air is determined. Instead of lifting the object in the air, the gripping force required for moving the object so as to be dragged is obtained. You can also
In the first and second embodiments, the finger part A is used as the gripping member. However, the present invention is not limited to this. For example, the arm part of the robot hand can also be used as the gripping member.

It is a perspective view which shows the robot hand which concerns on Embodiment 1 of this invention. FIG. 3 is a side view showing the configuration of the finger part of the robot hand according to the first embodiment. 3 is a cross-sectional view showing a configuration of an ultrasonic actuator that drives a finger portion in Embodiment 1. FIG. 3 is a partial cross-sectional view illustrating a configuration of a vibrating body used in the ultrasonic actuator according to Embodiment 1. FIG. 3 is a perspective view showing polarization directions of three pairs of piezoelectric element plates of the vibrating body in the first embodiment. FIG. FIG. 3 is a front view showing a state where an object is gripped by two finger portions in the first embodiment. FIG. 3 is a side view showing a state where two fingers are slid with respect to the side surface of the object in the first embodiment. FIG. 3 is a front view showing a state where two finger parts are slid with respect to the side surface of the object in the first embodiment. 4 is a graph showing a relationship between gripping force by each finger portion, load acting on each finger portion, and normal force received by an object in the first embodiment. 6 is a front view showing a state in which an object is lifted by two finger portions in the first embodiment. FIG. 6 is a side view showing a state where an object is lifted by two finger portions in the first embodiment. FIG. 6 is a perspective view showing a robot hand according to a modification of the first embodiment. FIG. FIG. 10 is a perspective view showing a robot hand according to another modification of the first embodiment. 6 is a graph showing a relationship between a gripping force by each finger part and a load acting on each finger part in the second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Control part, 2, 4 Vibrating body, 3, 5 Rotor, 11 Base part, 12 Stator, 13 Connection bolt, 14 Recessed part, 15 Step, 16 Holding member, 21-23 Piezoelectric element part, A finger part, C1 Section 1, C2 Section 2, C3 Section 3, U1, U2 Ultrasonic actuator, S object, T placement surface, W gravity, G gripping force, F load, N normal force.

Claims (5)

At least two gripping members;
An actuator for moving each gripping member;
Load detecting means for detecting a load acting on at least one gripping member;
In the state where the actuator is driven and the side surface of the object is gripped and lifted by at least two gripping members, the gripping force for sandwiching the object by these gripping members is gradually reduced and detected by the load detecting means. A control unit that determines the gripping force when a load acting in a direction along the surface of the object falls as a gripping force necessary when lifting the object. . The actuator is composed of an ultrasonic actuator using a piezoelectric element as a vibrating body. The load detecting means is formed by a piezoelectric element of the ultrasonic actuator and detects a load using an inverse piezoelectric effect generated in the piezoelectric element. The robot hand according to claim 1.   The control unit detects the weight of the object based on a gripping force of the object by at least two gripping members and a load acting in a direction along the surface of the object detected by the load detection unit. The robot hand according to claim 1, wherein a friction coefficient between at least two gripping members that grip the object and a surface of the object is detected.   The actuator according to claim 1, wherein the actuator is a multi-degree-of-freedom actuator having two or more degrees of freedom, and the actuator is movable in at least two directions: a direction in which the gripping member is gripped and a direction in which the gripping member is slid with respect to the object. The robot hand according to any one of the above.   The robot hand according to any one of claims 1 to 4, wherein the gripping member includes finger parts, and includes at least two actuators arranged corresponding to the finger parts and moving the corresponding finger parts. .

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