JPS6056893A - Active follow-up type joint device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active tracking joint device having two plates mechanically connected by a K-like structure having six links, wherein said links are each connected to the plate at its ends by a U-joint.

The invention is suitable for use in a robotic arm providing a fine adjustment wrist section movable in five or six degrees of freedom. The invention is still suitable for use in platforms that can be moved linearly and angularly into predetermined assist positions in assembly processes that do not require a complete robot.

With the advent of automated production, complex tasks have to be performed by robots, especially in the case of insertion and assembly, where joints located between the end element (typically a gripper) and the manipulator base are used. The device must be capable of elastic deformation so that small positioning errors do not induce levels of stress that can damage the system. Furthermore, the final positioning of the end element must be very precise and the magnitude of the applied force must be monitored.

Tracking devices such as those described above are known to those skilled in the art and are described, for example, in The Industry, June 1979.
H, McCa 11 to ial Robot.
A follow-up device for inserting a peg into a hole by n et al.
ca 1 antdevice for insert
fng a peg in a hole)” and U.S. Patent No. 4.2 to Brendanour.
83.153. McCalli
The device described by on is a passive tracking device in which each link consists of two parts connected by an elastic coupler and connected to the plate by a pole-soft type joint. There is.

The elasticity of such a system is sufficient to accommodate alignment errors. On the other hand, the passive nature of the structure does not provide the positioning accuracy needed in some applications, nor does it provide monitoring and control of trench forces.

Although several active joint devices for use as robot wrists are known to those skilled in the art, none of these devices satisfactorily meet the requirements described above.

In principle, a high degree of accuracy is usually achieved only under the disadvantage of severely limiting the load that can be carried. This high degree of accuracy further requires sophisticated actuators and detectors. The cost of the manipulator is therefore very high.

However, the high degree of accuracy achieved by complex configurations such as those described above is not required except at the final stage of the process.

Moreover, most of the joint devices designed to date do not have sufficient degrees of freedom (eg French Patent Publication No. 2,462,607). Such a device cannot be used in a robot unless the arm of the robot already has some degree of freedom that allows positioning of the end grits 9. In such cases, the tracking device may be designed to have only the degrees of freedom necessary to angularly position the gripper.

Prior art active devices typically use hydraulic or electric linear actuators. Monitoring and controlling the force of such actuators is somewhat difficult. First, hydraulic actuators are usually velocity controlled rather than position controlled, ie, the flow into or out of the actuator is controlled by a servo valve. Electric actuators typically use a transmission that includes a worm screw. Such transmissions are irreversible and do not allow for force monitoring (Assembl., February 1983).
y Automation, page 21:)). Hydraulic actuators are also used to adjust the position of the simulator's motion platform with six degrees of freedom (Kail
No. 3,577,659).

It may be noted that in this case too, said system does not provide compliance as well as force control, and compliance is more of a drawback than an advantage in such systems.

Finally, if the device does not present all the degrees of freedom necessary for insertion and assembly, force monitoring requires a significant 1k. For example, it would be very difficult to monitor forces when translational motion is transmitted through a robot arm, especially due to the inertia of the parts and the reduction ratios to be included in the linkage.

The present invention seeks to provide an improved active tracking joint device. The invention particularly aims at providing a device which allows the displacement of a load in six degrees of freedom without any transmission of motion from external elements, whereby the inertia of the moving parts is reduced and the detection is made easier. It becomes easier. The invention further aims to provide an active device in which force can be sensed and which can be controlled by processed signals received from a displacement sensor.

The present invention provides a device having an independent linear actuator for each link and a sensor arranged parallel to the actuator to detect linear movement of the parallel actuator.

The actuator is pneumatically operated (thereby providing compliance), double-acting and associated with a control system that regulates the gas pressure in both chambers of the actuator 9. It is reversible, has inherent flexibility based on the compressibility of the gas, and allows for control of the applied force, which controls the flow into or out of the chamber of the actuator. This can be accomplished by controlling on-off, off-valves controlled by current pulses with variable duty cycles.The inherent flexibility of pneumatic actuators allows for passive compliance in the event of accidental contact. This followability can be adjusted by adjusting the stiffness of the servo loop.

Preferably, the links are arranged to form three equilateral triangles evenly distributed around the axis of the device. Such a configuration simplifies the mathematical matrix that defines the correspondence between the forces exerted by the actuators and the small-scale translational and rotational movements of the actuator triplet in question. The sensors associated with each actuator typically consist of potentiometers or encoders that emit electrical signals that can be processed directly by a control computer often associated with the robot.

The invention will be explained in more detail below on the basis of specific embodiments by way of example.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS The articulating device described below is suitable for making a manipulator executable. This device can be placed between the manipulator arm and an end tool such as a Glitz-q. This device and the associated manipulator elements fulfill different functions fc. The above device achieves extremely precise positioning as well as control of the force exerted through the tool, while the manipulator provides approximate positioning during the approach. The assembly operation can therefore be carried out in two stages. First, the approximate relative positioning of the two parts to be assembled is made. The active articulation device then makes small movements for precise positioning.

In Figures 1-3 a device with %2 plays) 10 and 12 is shown. For convenience, the plates are referred to as an upper plate and a lower plate. For simplicity, it is assumed that the upper plate is connected to the arm of the manipulator and the lower plate receives the tool. The two plates are
cage-like structure] 4. To achieve the six degrees of freedom required for assembly, the cage has six links, each of which is adjustable in length. The car has a rotational symmetry of order 3 about the axis of the differential chair.

The link may be designed to define three adjacent equilateral triangles when at its installed or intermediate length. Thereby, a matrix is simplified that provides a correspondence between link lengths and translational and rotational movements.

Each link is constituted by an actuator 13 connected to an upper plate 10 and a lower plate 12 to enable the length of the link to be reduced. The actuator may be an air jack having a body or cylinder within which a piston coupled to a rod reciprocates. The body of each actuator has gimbal joint 1
It is connected to the plate 10 by a U-joint consisting of 5. The actuator rod is connected to the lower plate by a second gimbal joint 16 and ball bearings in a direct IJK arrangement (FIG. 4). The connection between the joint or the bearing and the plate can be realized by any conventional means, for example by screws and nuts.

Each actuator 13 is equipped with a displacement sensor 17 including a linear potentiometer. As shown in Figure 5,
The housing of the potentiometer can be connected to the body of the actuator 13 by means of a sleeve 18 and a collar 20. The slider of the potentiometer can be moved by the rod P of the actuator 13. The connection between the slider and the rond can be realized through a play 119 through which the rond ends are connected.

The independent movement of the six actuators 13 provides six degrees of freedom (translational and rotational movement).

The magnitude of movement is limited only by the operating range of the actuator. Since the actuator is located very close to the tool, the nature of the moving elements for fine adjustment is reduced to a minimum. By the use of pneumatic actuators), the tool can also be used to adjust its displacement and to reduce the force and torque exerted by the tool. It can also be controlled for adjustment. The force exerted by each actuator rod 12 can be controlled by chopping the excitation current that is connected to the chamber of each actuator via an air line and sent to the valve antagonist 1126. It has been found empirically that, at least when the system is close to equilibrium, the pressure change in the chamber of the actuator is substantially proportional to the duration of the electrical pulse sent to the corresponding solenoid valve to open the valve. . The degree of followability can be increased by changing the "stiffness" of the servo loop's response, as will be explained below.

A working force sensor may be located between each cardan or gimbal joint 16 and its associated plate 19. The output signal of the sensor may be applied to a servo loop that regulates the force exerted by the actuator and maintains the force at a predetermined magnitude. Said loop, fed with a signal, controls a solenoid valve 26. The degree of compliance can be adjusted by simultaneously increasing or decreasing the pressure in both channels of the actuator.

- The described device is associated with a gas source under pressure maintained at a constant value by a control system that may include a digital computer (not shown). A flowchart of the system is shown in FIG.

In FIG. 6, the input signals M and T represent the linear and angular position to be achieved in the relevant actuator triplet fixed with respect to the manipulator arm. The input signal is provided to a computer 23, which is programmed to simulate the inverse of the Denoys geometric model. The output of 23 representing the length to be given to the actuator 13 is:
- set of subtraction circuits 24, said subtraction circuits 24 also receiving a negative feedback signal from the detector 17.

The output signal of the subtraction circuit is given to the solenoid valve 25.

A-D if the sensor associated with the actuator to emit a signal indicative of extension is of the analog type.
A transducer (not shown) must be staged.

As shown in FIG. 7, the body and rod of each actuator are secured by pins or thin rods that provide sufficient rigidity while easily engaging during compression (10 and 12).
can be combined with Such forgings are particularly suitable for use in the micromechanical field.

Compared to gimbal joints and ball bearings, the range of relative motion of the pin is narrow. However, this is not a problem if the required movement is a small change. On the other hand, such a connection does not cause any movement.

The denomination chair according to the invention may be used as the wrist of a Grino/Q placed in a stationary position to receive parts inserted into the pond by a movable gripper supported by a robot. Followability is determined by manipulator grits q
The advantage is rather provided by the support of stationary parts.

[Brief explanation of drawings]

1 is a schematic isometric view of the device according to the invention showing the plate and the relative positioning of three of the six actuators of the device; FIG. 2 is a schematic isometric view of the device according to the invention showing only two actuators; Bottom view, Figure 3 is line 1 in Figure 2.
FIG. 4 is an enlarged detailed view showing the connection between a pair of actuators and one plate of the device of the invention, and FIG. 5 is a detailed view showing the connection between a detector and one of the actuators. , FIG. 6 is a schematic explanatory diagram showing a possible configuration of the control system and servo loop of the device of the present invention,
FIG. 7 is an explanatory diagram showing a modified example of the configuration in which the actuator is coupled to the end plate. 10.12... Plate, 13... Actuator, 14... Cage-like structure, 15.16... Gimbal joint, 17... Displacement sensor, 18... Sleeve,
19...plate, 2o...narato, 23...
Computer, 24... Subtraction circuit, 25, 26...
solenoid valve. Continuing from page 1 @ Inventor Claude Loubret = 7 Reims, 31300 Castanet-Trosens, Labège / Humain Cantreux (no street address)

Claims (1)

Claims: (11) An active tracking articulation device having two plates connected by a cage-like structure, wherein each cage-like structure is connected to two plates by a U-joint. each link includes an independently controlled reciprocating actuator and a sensor connected to provide a signal indicative of the amount of extension of the actuator, said actuator being controlled by gas pressure. and the actuators are associated with a control system that controls the air pressure in the two chambers of each actuator to modulate the force exerted by the actuator as well as the length of the actuator. Claim 1, characterized in that it comprises a set of two @magnetic valves associated with one of the chambers and means for controlling said solenoid valves to independently regulate the pressure in both chambers of the actuator. The device of claim 1. (3) The solenoid valve control means is configured to generate an electrical pulse having an adjustable duty cycle. (4) The device according to claim 1, characterized in that the links are arranged in such a manner as to define a plurality of equilateral triangles when at their installed length. 5) A device according to claim 1, characterized in that the sensor is a potentiometer. (6) Each actuator has two parts, one a body and the other a rod, One of these parts is connected to one of the two plates by a gimbal joint, and the other part is connected to the other plate by a gimbal joint and a bearing. A device according to paragraph 1. (7) Each actuator has two parts, one a body and the other a rod, the rod and the body being connected to each one of the two plates and subject to bending stress. The device according to claim 1, characterized in that the device is connected by a flexible rod configured to curve while resisting an axial force when subjected to an axial force. (8) 6 freedom an active compliant articulation device having an upper plate, a lower plate substantially parallel to the upper plate along an axis, and a rotationally symmetrical joint with respect to the axis, the upper plate and the lower plate having rotational symmetry about the axis; a cage-like structure mechanically coupled to the plate, said structure including six links each extending diagonally between an upper plate and a lower plate, each link having a A double-acting actuator having two relatively movable parts each connected to one of the upper and lower plates by a U-joint, wherein an increase in gas pressure within either one causes extension of the actuator, and a double-acting actuator having two chambers configured such that an increase in gas pressure inside the other causes retraction of the actuator; the actuator exerts its effect by independently controlling the gas pressure in the two chambers of each actuator; A control system that adjusts force and actuator length to provide followability;
and a sensor for emitting a signal to the control system representative of the amount of extension of the actuator.