JPH04300179A - Wire interference drive system for robot arm - Google Patents

Abstract

PURPOSE:To provide a highly controllable wire drive system having a simple structure, for driving a robot arm. CONSTITUTION:A number (n) of link members are coupled together by the number (n) of joints, two wires being set to n-th joint, fours to (n-1)-th joint, four wires to (n-2)-th joint, a minimum even number of wires which exceeds (1+1), to (n-1)-th joint, and a minimum even number of wires which exceeds (n), to 1-th joint, and the tensions of these wires are controlled to generate a predetermined torque from a desired joint. Therefore, a group of desired torques at joints are at first determined, and a group of tensions of wires which may satisfy the desired torque group and with which the axial force of the final base end joint becomes zero is obtained, the value which is (n) times large as a minimum tension of wires in the group is used as a set value to the axial force of the final base end joint, thereby a group of tensions of wires which satisfy the group of the desired torques and the set value to the axial force of the final base end joint are obtained. Further, a torque servo using feed-back signals from sensors of a joint tension differential type is carried out to eliminate affection by a frictional loss in a pulley section.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire interference drive system for driving a robot arm.

0002

2. Description of the Related Art A robot arm has a plurality of links and a plurality of joints connecting the links. The robot arm has multiple links, from the link at the proximal end closest to the drive system side to the link at the tip where work is performed, and adjacent links are connected by joints, and each link is generated The force exerted is determined by the torque of each joint. Each joint is driven by an actuator.

However, since the actuators that drive the joints are heavy, attaching the actuators directly to the joints is disadvantageous in terms of output weight ratio, and it is especially advisable to attach the actuators to the joints near the tips of the robot arms. Instead, it is necessary to attach the actuator at a position closer to the drive system than the target joint, and to transmit the driving force from the actuator to the target joint by some means.

[0004] Such a wire pulley drive system is used, for example, in the Stanford/JPL hand (Robot
Hands and the Mechani
cs of Manipulation by M
．． T. Mason and K. J.
Salisbury- The M.I.T.P.
ress) and CT arm (Hirose, Ma, “Development of a wire-interference-driven multi-joint manipulator,” Proceedings of the Society of Instrument and Control Engineers, Vol. 26, No. 11,).

[0005]

However, in these conventional techniques, for example, in the Stanford/JPL Hand method, the tension of each wire is measured at one location, and the influence of friction loss at the pulley cannot be ignored. Also, the CT arm method is 2 for a robot arm with n joints.
n wires are required, which increases the number of required wires and complicates the structure of the drive system. For these reasons, it is desired to develop a wire interference drive system for a robot arm that is lighter, requires fewer wires, is slimmer, has better controllability, and can be manufactured at a lower cost.

[0006] This invention was made in view of the above circumstances, and is lightweight and requires a small number of wires.
It is slimmer and cheaper to manufacture, more wires can be hung on the joints closer to the base, and even with a uniform wire drive system, the joints closer to the base can generate more torque. , it is possible to standardize the equipment parts of the wire drive system, and it is also possible to directly measure the torque of each joint with a tension-activated torque sensor placed near each joint axis. The object of the present invention is to provide a wire interference drive system for a robot arm that can eliminate the influence of friction loss in a pulley by feeding back joint torque to a control system.

[0007]

[Means for Solving the Problems] Corresponding to this object, the wire interference drive system of the robot arm of the present invention provides n
This is a wire interference drive system that drives a robot arm with joints, in which the same number of pulleys as the number of wires hanging on each joint are installed so that they can rotate independently of each other, and the minimum even number of pulleys exceeding n Prepare a wire, and the wire that hangs on each joint axis wraps around the pulley for more than one turn, passes through that joint axis, and then the wire that hangs on that joint axis.
When the number of wires hanging on the joint axis next to the proximal end is the same as the number of wires hanging on the joint axis next to the proximal end, two wires among the wires hanging on the joint axis will be attached to the link member on the most distal side of the joint axis. It is fixed, and two wires are attached to the joint at the tip.
The most proximal joint has the smallest even number of wires exceeding n.
is applied, and the (n-i)th joint from the most proximal end is (i
The minimum even number of wires that exceed +1) should be applied, and the even number of wires that are applied to each joint axis should be the total number of the same number of forward rotation wires and reverse rotation wires, and the tension of each wire should be It is characterized by controlling to achieve a predetermined torque of the target joint.

[0008]

[Operation] n link members are connected by n joints, 2 for the nth joint from the base end, 4 for the (n-1)th joint, and 4 for the (n-2)th joint. There are four joints,..., (n-i
)th joint has the smallest even number exceeding (i+1),
..., the smallest even number of wires exceeding n are hung on the first joint, and the tension of each wire is controlled to generate a predetermined torque at the target joint. To do this, first determine the target torque set for each joint, find the wire-tension set that satisfies the target torque set and makes the axial force of the proximal joint zero, and then find the minimum wire tension set in that set. A wire that satisfies the target torque set and the set value of the axial force of the joint at the most proximal end, with n times the tension of the wire as the set value for the axial force at the joint at the most proximal end.
Find the set of tensions. In addition, torque servo is performed using feedback signals from each joint tension differential type sensor to eliminate the effects of friction loss in the pulley section.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to the drawings showing the embodiments. FIG. 1 shows a robot arm 1 with seven joints. The robot arm 1 includes link members L1 to L7 extending from the base end on the drive system side to the tip end on the hand side, and each link member L1 to L7 is connected to an adjacent link member at joints J1 to J7. Joint J1
-J7 joint axis Z1 -Z7 has the same number of pulleys P (P11-P72 as the number of wires W passing through it).
) are installed so that they can be rotated independently.

The connection state of each part is as follows. i-th
The pulley P is rotatably coupled to the shaft, except in the following cases. Link Li and link Li-1 are Zi
They are rotatably connected via a shaft. Idle pulley a
i rotates the direction of motion of the cable by 90 degrees. That is, the joint axis Z1 of the joint J1 has a pulley P.
11-P18 are installed to be able to rotate independently.

A pulley P is attached to the joint axis Z2 of the joint J2.
21-P28 are installed to be able to rotate independently. The joint axis Z3 of the joint J3 includes pulleys P31-P36.
are installed so that they can be rotated independently. The joint axis Z4 of the joint J4 has pulleys P41-P46.
are installed so that they can be rotated independently. The joint axis Z5 of the joint J5 has pulleys P51-P54.
are installed so that they can be rotated independently. The joint axis Z6 of the joint J6 has pulleys P61-P64.
are installed so that they can be rotated independently. Pulleys P71-P72 are installed on the joint axis Z7 of the joint J7 so as to be able to rotate independently.

[0012] The smallest even number of wires W1 exceeding the number of joints n - n+1 or n+2 (in the case of this embodiment)
8) and connect the pulleys P1 -P as described below.
Wrap it around 72. The even number of wires hung on each joint axis is the total number of the same number of forward rotation wires and reverse rotation wires. Idle pulleys a11-a71 are used to change the direction of the wire by 90 degrees.

Each wire-drive path is as follows. (Wire-1) Wire-1 From the drive system, wrap around pulley P11 once, pass through idle pulley a11, wrap around pulley P21 once, pass through idle pulley a12, wrap around pulley P31 for 1.25 times, idle pulley a13 , a14, wraps around pulley P41 once, passes idle pulley a15, and wraps around pulley P51.
It wraps around 25 times, passes through idle pulley a16, wraps around pulley P61 once, wraps around pulley P71 once, and is fixed to link member L7.

(Wire-2) From the wire-2 drive system, wrap it around the pulley P12 once and connect it to the idle pulleys a21 and a.
22, wraps around pulley P22 once, passes through idle pulleys a23 and a24, wraps around pulley P32 once, passes idle pulley a25, and wraps around pulley P42.
, passes through idle pulleys a26 and a27, wraps around pulley P52 for 1.5 turns, passes through idle pulley a28, wraps around pulley P62 once, wraps around pulley P71 once, and is fixed to link member L7.

(Wire-3) From the wire-3 drive system, wrap it around the pulley P13 once and connect it to the idle pulley a31, a.
32, wraps around pulley P23 once, passes idle pulley a33, wraps around pulley P33 for 1.25 times, passes idle pulley a34, wraps around pulley P43 once, passes idle pulleys a35 and a36, then pulley Wrap around P53 for 1.5 turns, idle pulley a
37, wraps around pulley P63 once, and is fixed to link member L6.

(Wire-4) From the wire-4 drive system, wrap it around the pulley P14 once and connect it to the idle pulleys a41 and a.
42, wraps around pulley P24 once, passes idle pulley a43, wraps around pulley P34 for 1.25 times, passes idle pulley a44, wraps around pulley P44 once, passes idle pulley a45, and wraps around pulley P54. It wraps around 1.25 times, passes through idle pulley a46, wraps around pulley P64 once, and links member L6.
Fixed.

(Wire-5) From the wire-5 drive system, wrap it around the pulley P15 once and connect it to the idle pulleys a51 and a.
52, wraps around pulley P25 once, passes through idle pulley a53, wraps around pulley P35 for 1.5 times, passes through idle pulley a54, wraps around pulley P45 once, and is fixed to link member L4.

(Wire-6) From the wire-6 drive system, wrap it around the pulley P16 once and connect it to the idle pulleys a61 and a.
62, wraps around pulley P26 once, passes through idle pulley a63, wraps around pulley P36 once,
It passes through idle pulley a64, wraps around pulley P46, and is fixed to link member L4.

(Wire-7) Wire-7 starts from the drive system, wraps around the pulley P17 once, passes through the idle pulley a71, wraps around the pulley P27 once, and connects to the link member L2.
Fixed.

(Wire-8) Wire-8 starts from the drive system, wraps around the pulley P18 once, passes through the idle pulley a81, wraps around the pulley P28 once, and connects to the link member L2.
Fixed.

[0021] The torque of each joint J1 to J7 is detected by a tension differential type torque sensor. As such a tension differential type sensor, Patent Application No. 2899 filed in 1988 is known.
No. 98 can be used. In the wire interference drive mechanism of the robot arm having such a configuration, the torque of the target joint is achieved by controlling the tension of each wire.

The tension of each wire is controlled and the torque of the target joint is determined as follows. First, the relationship between wire tension, pulley diameter, joint torque, and axial force of joint J1 is as shown in Equation 1 below.

[0023]

[Equation 1] Here, fi: Tension of wire i (fi ≧0) τi: Torque of joint Ji P1: Axial force of joint J1 (sum of all wire tensions) A
;8x8 transformation matrix determined by pulley diameter and wire placement method

Each wire - method for determining tension 1. Determine target joint torque τri (i=1 to 7). The DCC method, use of JT, and other methods can be used to determine the target joint torque.

2. Calculate Equation 2.

[Math 2]

3. Find the minimum fi. min(fi) (i=1~8)

[0027]
4. A target value Pr1 of the axial force of the pulley 1 is determined using Equation 3.

[Math 3]

5. Calculate Equation 4 again and get the target tension fri
Find (i=1 to 8).

[Equation 4] *However, as a simple method, there is also a method of setting Pr1 to a sufficiently large positive value.

6. According to Equation 5, a torque servo is performed using the feedback signal τsi (i = 1 to 8) from each joint tension actuated sensor, and the tension f to be applied to each wire is
ai (i=1 to 8) is determined and added by each wire drive system.

[Equation 5] *However, PID{・} is the joint torque deviation (τri−τ
si) (i=1 to 8).

[0030]

Effects of the Invention In the wire interference drive system of the robot arm of the present invention, the number of required wires is as small as ``the minimum even number exceeding n''. This makes it possible to produce a lightweight, slim, and inexpensive robot arm. Also, the closer the joint is to the base, the more wires are attached to it. As a result, even if a uniform wire drive system is used, larger torque can be generated at the joints closer to the base. Also, the wire drive system can be made into a common component. Furthermore, each joint torque can be directly measured using a tension-activated torque sensor placed near each joint, and by feeding back the measured joint torque to the control system, friction loss at the pulley can be reduced. can remove the influence of Therefore, according to the present invention, it is possible to obtain a wire interference drive system for a robot arm with good controllability.

[Brief explanation of drawings]

FIG. 1 is an explanatory front view showing the configuration of a robot arm.

FIG. 2 is a perspective explanatory view of a tension-activated torque sensor.

FIG. 3 is a perspective explanatory diagram showing the routes of all wires.

FIG. 4 is a perspective explanatory view showing the route of the wire 1.

FIG. 5 is a perspective explanatory view showing the route of the wire 2. FIG.

FIG. 6 is a perspective explanatory view showing the route of the wire 3. FIG.

FIG. 7 is a perspective explanatory view showing the route of the wire 4. FIG.

FIG. 8 is a perspective explanatory view showing the route of the wire 5. FIG.

FIG. 9 is a perspective explanatory view showing the route of the wire 6. FIG.

FIG. 10 is a perspective explanatory view showing the route of the wire 7. FIG.

FIG. 11 is a perspective explanatory view showing the route of the wire 8. FIG.

[Explanation of symbols]

1 Robot arm 11 Torque detection sensor W Wire L Link member J joint a Idol pulley P Pulley A Wire drive system

Claims (1)

[Claims] Claim 1: A wire interference drive system for driving a robot arm having n joints, in which pulleys of the same number as the number of wires hanging on each joint are installed so that they can rotate independently of each other, and the robot arm has n joints. Prepare the minimum even number of wires that exceed If the number of wires hanging on the joint axis next to the joint axis is the same as the number of wires hanging on the joint axis, two of the wires hanging on that joint axis are fixed to the link member on the most distal side of the joint axis. Two wires are connected to the joint at the most proximal end, and the smallest even number of wires exceeding n are connected to the joint at the most proximal end, and from the most proximal end (n-i)
The minimum even number of wires that exceed (i+1) is hung on the joint, and the even number of wires that are hung on each joint axis is the total number of the same number of forward rotation wires and reverse rotation wires. , a wire interference drive system for a robot arm that is characterized by controlling the tension of each wire to achieve a predetermined torque at a target joint.