JPH03196983A - Control method for human type robot finger mechanism - Google Patents

Abstract

PURPOSE:To enable it to assign a human type robot fingertip to the extent of human 4-degree-of-freedom by making a first joint, or a joint at the most fingertip side in human type robot fingers, control a joint rigidity or inner force sense-contact force sense, while making the rest joints perform position control where a virtual fingertip is set up. CONSTITUTION:A first joint 1 in human fingers is much in case of interlocking with a second joint, and such a requirement that a first joint angle theta4 of a robot finger is strictly specified is considered as not so much necessary even in consideration of the highly functional working property of the human finger. Accordingly, positioning of this first joint 1 is not performed, and only rigidity of the joint doing in consideration of force control of the fingertip based on force information being secured from an inner force or contact force sensor attached to the fingertip, or 'surface hardness' in a holding object is controlled, so that each fingertip position is determined from remaining joints 2-4, namely, respective angles theta1-theta3 of these residual joints 2-4 are determined from the fingertip part overrode the rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for controlling a humanoid robot finger mechanism, and is devised to facilitate positioning control by introducing the concept of virtual fingertips.

<Prior Art> The technology of robot finger mechanisms has not yet gone beyond grippers (about one degree of freedom), and there are few robot finger mechanisms that have a human finger structure. High-performance robot finger mechanisms include the University of Utah hand in the United States, the JPL/Stanford hand, and in Japan, the Institute of Electronics and Technology (3-finger hand), the Institute of Mechanical Technology (5-finger hand), and the Institute of Mechanical Engineering (5-finger hand). These include the Waseda University (E-Usician robot, five-fingered hand) and the Mitsubishi Heavy Industries extreme work robot hand (four-fingered).

The structure of the robot hand is such that the actuator is an electric motor or a hydraulic or pneumatic cylinder, the fingers are driven by a wire pulley system, and the degree of freedom configuration is almost the same as that of a human finger.

<Problem that the invention seeks to solve> Force sense in the robot finger mechanism as mentioned above.

Few machines are equipped with pressure sensors or other sensors, and their control is centered on position and speed control.

In addition, the research target of conventional robot finger mechanisms is how to access the object to be grasped using three, four, or five fingers, that is, how to coordinate and control each finger. Rather, it is often discussed as a method of controlling the arm.

More specifically, a robot finger that imitates the human finger structure has a joint structure with four degrees of freedom, as shown in FIG. Therefore, in a three-dimensional space, if we ignore the posture caused by the rotation of the fingertips and try to determine the angle of each joint simply from the fingertip positions (P, , P, , P), Si==om6 i Ci =cmθIC1j=ca
o(θ1+θJ), etc. In this case, the relationship between the fingertip position and each joint angle is as shown in equation (1). That is, P, =...P-, P=...
From the three equations, each joint angle θ1. θ2. θ2. θ
4 and four variables must be determined, making it impossible to arbitrarily determine the joint angles θ, ˜θ4. Therefore,
It is necessary to specify the finger in addition to the fingertip position (P, , P, , P, ) to find each joint angle θ, ~θ4.

In other words, it becomes necessary to perform more complex calculations, and
Taking into account the orientation due to rotation significantly impairs intuitiveness in fingertip designation (teaching, work planning).

Therefore, as the number of fingers increases from three to four,
In order to position the entire finger, a rotational posture is required, and the position specification becomes increasingly complicated and unintuitive.

Therefore, if the complexity caused by rotational posture is resolved without losing the functionality of robot fingers, the position of each fingertip can be determined by simply specifying (xp ys z), and positioning control can be performed. can be simplified.

Furthermore, as shown in FIG.
If you try to rotate it by holding it with 21, 22, or 23, it is necessary to set the fingertip position taking into consideration the "hardness" and surface friction of the cylinder (object) 25, and it is impossible to specify the exact position. .

In view of the above-mentioned prior art, the present invention aims to provide a method for controlling the humanoid robot finger 8ji#i4, which allows easy control.

Means for Solving the Problems> The structure of the present invention that achieves the above object is based on the following knowledge.

In other words, the first joint (corresponding to θ4) in a human finger often moves in conjunction with the second joints (six), and it is difficult to precisely specify the first joint angle (θ4) of a robot finger.
Considering the highly functional workability of human fingers, this seems not to be very necessary.

Therefore, in the present invention, the positioning of this first joint (θ4) is not performed, and the force control of the fingertips is performed based on force information obtained from the force sense or pressure sensor attached to the fingertips. The stiffness of the joints is only controlled by considering the stiffness (rigidity), and θ4. θ2. Determine the fingertip position from θ3, that is, the fingertip position ignoring rotation (xp
yp z), determine θ, ~θ, and (Xy y#Z
) Achieving a solution to the roughness of the rotational posture of fingers on a plane.

Therefore, the configuration of the present invention is a method for controlling a humanoid robot finger 81 structure that is driven by an actuator capable of force control and has a maximum of four degrees of freedom. The special effects feature is that one joint controls joint stiffness, force sense, and pressure sense, and the remaining joints perform position control by setting virtual fingertips.

According to the present invention having the above configuration, the unknowns are the maximum of three joint angles θ, ~θ3, so the fingertip positions (P, , P, ,
By specifying P, ), the position of the fingertip is controlled.

Example of implementation Hereinafter, embodiments of the present invention will be described in detail based on the number of times.

In this embodiment, as shown in FIG.
This is applied to a robot finger with 4 degrees of freedom that has 4 degrees of freedom.For this robot finger, the fingertip position (PX,
By specifying P,, P□), each joint angle θ, ~
This is to determine θ3.

By the way, the virtual fingertip position is 1”=l+a-1...(4) 0<a<1 Determine as.

Here, -2 is simply the combined height of the finger links 13 and 14, but it is given by the above equation (4) using a weighting coefficient α. The value of a is weighted according to the type of work and is determined in advance, for example, as shown in the table below, and the value is determined for each type of work.

Work Motion and Weighting Coefficient α In other words, it is assumed that the value of a specifies the virtual contact point of the fingertip to the grasped object. At this time, the first joint is
It is sufficient to control information regarding force (rigidity is also possible), such as a constant force when pressing the object against the object.

The working motions of the robot fingers are shown in FIGS. 2 to 5 in correspondence with the tasks in the relationship table a.

(Al Nigiri (Figure 2; Thumb 202, index finger 21,
Middle finger 22. When gripping the cylinder 25 with the ring finger 23) It is considered that the link (vi of the finger) of the second joint is often in contact with the cylinder 25. Figure 2 (aL (bl
As shown in the figure below, you can specify the point where the object will ignite when it comes into contact with it.

For example, if the first joint is always pressed with a constant force (fco, t), the contact with the cylinder 25 will always be maintained.

(b) Pinch (Fig. 3; When rotating the cylinder 25 by pinching it with the thumb 20, big finger 21, middle finger 22, and ring finger 23) The link of the first joint (the pad of the finger) is in contact with the cylinder 25. There is. The position specification follows the above-mentioned rule. For example, if you try to rotate the cylinder 25 as shown in Figure 3(a), Tbl, simply Pi (i=o, 1, 2,
If 3) is designated as a position rotated around 0 for Pi', movement can be realized while always maintaining contact with the cylinder 25 without considering twisting of the finger. Pull (4th)
The same concept can be used for pressing and rubbing (Fig. 5).

Taking as an example a case where a triangular prism is rotated by a humanoid robot finger mechanism (a case involving a pinching operation), this example is shown in Fig. 6 (
A more detailed explanation will be given based on al, (b).

In this example, in order to simplify the explanation, the triangular prism 24 is rotated around two axes within the x and y planes. In this case, the fingertips in the XpY plane (thumb 20 degrees, index finger 21, middle finger 22, ring finger 2
The position of 3) is Pi (xi, yi) → P'i (x'i, y'i) → P
'i (x'i, y'i).

On the other hand, the contact between the fingertip and the triangular prism 24 is as shown in FIG. 7(a). In the figure, the joint angle θ41 of the first joint 1
153 It is not necessary to define it closely, and the pad of the finger should be a triangular prism 2.
All you have to do is touch 4 (To point). Also, Figure 7 (
bl is a length l, +al, and if the virtual fingertip located ahead of the second joint 2 is set to point T' (virtual contact point), the first joint 1
This is an explanatory diagram illustrating that if the force is controlled such that the contact point T is pressed with a constant force (fc. . . . ), the contact point T with the triangular prism 24 can always be achieved. Therefore, the same effect as in Figure 4) can be obtained, and the coordinates on the Z axis are also determined.

The position V in the X, y, Z space determined in this way
! From lPi (xi, yi, zi), equation (3)
Solve the simultaneous equations for each joint angle θ, ~θ.

is calculated and output to the actuator driving each joint.

Similarly, the To point in Figure 7(a) is also To (x, yp Z
), but as mentioned in the <Problem to be Solved by the Invention> section above, in the case of four joints, the formula (
According to 1), even if an attempt is made to find each joint angle 01 to θ4, a solution cannot be obtained because the three-dimensional system has four variables. Therefore, in the case of B, it is necessary to specify a method for specifying the attitude C mouth by rotation, pitch, yaw, Euler angle, etc. [Formula (2)].

Although this method is already established and can determine 10 points, it is necessary to take into account twisting of the fingers due to friction with the object, and the problem is that it becomes extremely complicated, especially when dealing with object manipulation. There is.

FIG. 8 is an explanatory diagram showing an example of a drive system of a robot finger mechanism to which this embodiment is applied. As shown in the figure, the drive system B uses an electric motor 10 as an inductor, and connects a finger link drive pulley 17 that constitutes a finger joint via a wire 12.
Moving gjA realizes the movement of the fingers. At this time, position control is performed using information such as the position sensor 11 that detects the rotation angle of the electric motor 10 or the position U sensor 15 that detects the rotation angle of the joint. in short,
Any method that allows the rotation angle of the finger joints to be controlled freely is fine. In addition, force control is performed by a force sensor 13 attached to the finger link 16 or a wire 12 connected to the finger link drive pulley 17.
This is done using information from the tension sensor 14 etc. installed in the This is also the same as in the case of position 1iIlfil, so long as the force can be freely manipulated. Joint stiffness control may be performed by varying the position feedback gain, the feedback gain, or the like. In short, both can be realized by using conventional control techniques.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, positioning in the three dimensions of x, y, and z is generally performed using the X#V#z position and the rotation around each axis. The rotation of i? must be specified using a total of six variables and each joint angle must be determined. With the three x, y, and z positions with good ffIQ characteristics, it is not only possible to specify the fingertips of the humanoid robot with up to 4 degrees of freedom, but it is also expected to have an effect equal to or greater than the effect that takes into account the rotational posture. can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a humanoid robot finger with four degrees of freedom to which an embodiment of the present invention is applied, FIGS. a) is an explanatory diagram showing how the triangular prism is held when the robot fingers rotate the triangular prism, FIG. 6 is a perspective view showing the triangular prism being gripped, and FIG. FIG. 8 is an explanatory diagram showing an example of a drive system of a robot finger mechanism to which an embodiment of the present invention is applied. In the drawings, 1 is a first joint; 2 is the second joint, 3 is the third joint, 4 is the fourth joint, θ1.θ2.θ5.θ4 are the joint angles. 1 (al Ib) Figure 6 (O<a<+)

Claims (1)

[Claims] Driven by a force-controllable actuator, up to 4
A method for controlling a humanoid robot finger mechanism with degrees of freedom, in which the first joint, which is the joint closest to the fingertip of the humanoid robot finger, controls the joint stiffness, force sense, and pressure sense, and the remaining joints control the virtual A method for controlling a humanoid robot finger mechanism, characterized in that position control is performed by setting fingertips.