JPH08241107A - Software safety joint for robot - Google Patents

Abstract

PURPOSE: To provide the software safety joint consisting of a force sensor and a simple software processing means in combination. CONSTITUTION: The force sensor 3 is fitted between the wrist tip part of the robot 1 and a tool and while data on detected six axial forces are written in a buffer in a robot controller 2 in short period, a next process is executed repeatedly in short period. Namely, the latest data f1, f2...f6 showing the six axial forces are read out of the buffer, an evaluation function g(f1, f2...f6)=a1|f1|+a2|f2|+...+a6|f6| is calculated, and the result is compared with a previously set allowance limit G0. When the allowance limit GO is exceeded, a robot stop signal is outputted immediately. If interference is caused during the operation of the robot 1, the robot 1 is stopped before a force which is large enough to break a robot mechanism part, the tool, etc., is applied, so that an increase in external force exceeding it is evaded. Any optional allowance reference for making a safety/danger decision is usable on condition that the magnitude of a vector <f>=(f1, f2...f6) can roughly be evaluated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique of a joint equipped on an industrial robot (hereinafter, simply referred to as "robot"), and more specifically, a mechanical portion of the robot and a tip portion of a wrist of the robot. A safety joint that can protect the tool attached to the machine from mechanical shock when it interferes.

[0002]

2. Description of the Related Art A tool (hand,
If visual sensors are used, they are included. The same applies below. ) Is attached to the robot to operate, the tool may collide with the work or other peripheral equipment and cause an interference accident. In the event of an interference accident, the robot's mechanical parts or tools may be damaged by the mechanical impact of the collision. As a means for avoiding such a situation, a method using a safety joint has been conventionally known.

[0003] One type of conventional safety joint has a mechanism including a relatively fragile member (for example, a casting having a predetermined brittleness) between the wrist end of the robot and the tool. Another type of conventional safety joint is one in which a mechanism using a spring is provided between the tip of the wrist of the robot and the tool to release the impact force acting on the tool from a predetermined direction at the time of collision.

In the former case, if a strong impact acts on the tool, the safety joint itself will be destroyed and must be replaced. The inability to reuse the safety joint is economically disadvantageous and the replacement work is complicated. Also, unless sufficient spares are always prepared, robot work cannot continue. Furthermore, there is a problem that the strength of the joint (the critical point at which it breaks) cannot be adjusted.

In the latter case, there is a problem that only the impact force from a limited direction can be released. Strength adjustment (adjustment of spring strength) is also difficult in practice.

[0006]

Therefore, the object of the present invention is to overcome the above-mentioned problems of the prior art, to prevent the joint itself from being destroyed, and to effectively function against impact forces from multiple directions. To provide a joint. Another object of the present invention is to provide a safety joint whose strength can be easily adjusted. Furthermore, the present invention intends to improve the safety, efficiency and economical efficiency of the work using the robot through these things.

[0007]

In order to achieve the above object, the present invention provides a force sensor mounted between a tip of a wrist of a robot and a tool, a software processing means, and the force applied to the software processing means. This is a software safety joint provided with software means for executing software processing related to the output signal of the sensor.

The software process includes a process for determining the relationship between the 6-axis force detected by the force sensor and a preset acceptance standard, and a process for controlling the robot according to the determination result. Is included. A robot controller is usually used as the software processing means.

Further, a typical process according to the determination result is a process of outputting a stop signal of the robot.
Here, the 6-axis force detected by the force sensor is the X, Y, and Z components of the force in the sensor coordinate system and the torque around each component (around each of the X, Y, and Z axes). These six components are represented by f1, f2 ... F6.

The allowable standard for the 6-axis force detected by the force sensor is a vector <f> = (f1, f2 ... f6) having the 6-axis force detected by the force sensor as a component.
Is set to roughly evaluate the size of. Examples of preferred acceptance criteria are:

[Acceptance Criteria 1] Magnitude of each component of 6-axis force detected by the force sensor | f1 |, | f2 | ... |
f6 | For allowable limits F1, F2 ... F6 (both are positive values). [Acceptance criterion 2] Evaluation function g (f1) having 6-axis force components f1, f2, ..., F6 detected by the force sensor as variables
, F2 ・ ・ ・ f6) = a1 │f1 │ + a2 │f2 │ +
... + a6 | f6 | (However, a1, a2 ... a6
Defines the allowable limit G0 of the constant of the same sign). [Acceptance criteria 3] Evaluation function h (f1) having 6-axis force components f1, f2, ..., F6 detected by the force sensor as variables
, F2 ... f6) = b1 f1 ² + b2 f2 ² + ...
+ B6 f6 ² (where b1, b2 ... b6 are constants with the same sign) defines the allowable limit H0.

[0012]

The signal representing the 6-axis force detected by the force sensor attached between the tip of the wrist of the robot and the tool is transmitted to the software processing means (usually the robot controller). The software processing means determines the relationship with the acceptance standard by software processing. In light of the acceptance criteria,
When it is determined that the detected force / moment deviates from the permissible range, processing for outputting a robot control signal for ensuring safety is performed.

The most common robot control signal for ensuring safety is a robot stop signal. In some cases, the position loop gain Kp and velocity loop gain Kv of each axis are switched to small values. It is also possible to output an alarm signal or a robot stop signal.

It can be considered that the mechanical parts of the robot, the tool, and the like are damaged when a very large force / moment is applied to the tool as compared with the normal time. And
In such a case, naturally, the magnitude of the vector <f> (norm of the vector) having the six-axis forces f1, f2, ... F6 detected by the force sensor as components is also very large.

Therefore, the vector <f> = (f1, f2 ... f) having the components of the six-axis force detected by the force sensor
6) The size of (at least) is roughly evaluated, and the size of the (at least) roughly evaluated vector <f> is an acceptance criterion that is properly determined in consideration of the strength and safety factor of the robot mechanism or tool. If the number exceeds the above, measures should be taken to ensure safety.

The above [acceptance criteria 1] to [acceptance criteria 3] are
It is an example of a preferable acceptance standard defined according to such a concept.

Allowable limits F1 and F in [tolerance standard 1]
2 ... F6 (both are positive values), F1 = F2 = ...
・ = F6 is the easiest to set, but the allowable limit may be set separately for the force component and moment component. In addition, if a direction that is particularly unfavorable when a force or moment is applied is predicted on the coordinate system of the force sensor,
The permissible limit for the component can be set small. For example, when the Z-axis direction of the sensor coordinate system is substantially coincident with the axial direction of the tool and the tool is weak in compression,
It is preferable to set a small allowable limit of the magnitude of force in the Z-axis direction of the sensor coordinate system.

Evaluation function g (f1
, F2 ・ ・ ・ f6) = a1 │f1 │ + a2 │f2 │ +
..... For the coefficients a1 to a6 of + a6 | f6 |
The simplest is to set a1 = a2 = ... = a6 (> 0), but it may be set separately for the force component and the moment component. Further, if there is a component evaluated particularly heavily, it is preferable to set the value of ai corresponding to the component relatively large.

Evaluation function h (f1 in [Criteria 3]]
, F2 ... f6) = b1 f1 ² + b2 f2 ² + ...
The same applies to the coefficients b1 to b6 of + b6 f6 ² . That is, it is easiest to set b1 = b2 = ... = b6 (> 0), but it may be set separately for the force component and the moment component. If there is a component that is evaluated particularly heavily, it is preferable to set the value of bi corresponding to the component to be relatively large.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an arrangement for using a robot equipped with a software safety joint according to the present invention by taking a fitting application as an example.

In FIG. 1, reference numeral 1 is a robot body,
It is connected to the robot controller 2 via a cable 11. The structure itself of the robot (main body) 1 is not particularly different from the conventional structure. In addition, the robot controller 2
As for the above, the same as those conventionally used may be used, except for software means for executing the processing described later.

At the tip of the wrist of the robot 1, there is attached a force sensor 3 for detecting a translational force in the X, Y, and Z axis directions (on the sensor coordinate system) and a six-axis force having a moment around these axes as components. ing. The force sensor 3 and the robot controller 2 are connected by a cable 31.

A set of works to be fitted is shown by reference numerals 4 and 5, and a work 4 having a projection 41 which functions as a guide pin at the time of fitting is provided to the robot 1 via the force sensor 3. It is installed. Further, the work 5 having the holes 51 is positioned on the work table 6.

FIG. 2 is a block diagram showing an outline of a system used in the above arrangement. Referring to FIG. 1, the entire system includes a robot controller 20, a robot (main body mechanism section) 1 controlled by the robot controller 20, a 6-axis force sensor 3 supported by an arm tip of a robot body, and a force The signal processing device 30 processes the detection signal of the sensor 3.

The robot controller 20 has a central processing unit (hereinafter referred to as CPU) 21. , The CP
The U21 has a memory 22 including a ROM, a memory 23 including a RAM, a non-volatile memory 24, and a teaching operation panel having a keyboard for inputting various commands or setting values for teaching of the robot and the operation of other system parts. 25, an input / output device 26 that performs an interface function with the signal processing device 30, and a robot axis control unit 27 that controls the operation of each axis of the robot body 1 via a servo circuit 28. It is connected.

As the force sensor 3 mounted on the tip of the arm of the robot body 1, for example, a well-known structure having a plurality of bridge circuits which are composed of strain gauges and are AC-driven by an oscillator can be used. The force sensor 3 outputs a detection signal representing the six-axis force components f1, f2 ... F6 to the signal processing device 30.

The outline of the signal processing in the signal processing device 30 is as follows. Each detection signal output from the force sensor 3 is amplified by a differential amplifier, synchronously rectified and converted into a DC signal, and then input to a multiplexer in the signal processing device. The multiplexer sequentially sends out the detection signals representing each component to the input / output device 26 via the sample hold circuit and the A / D converter in accordance with the control signal received from the CPU 21 of the robot controller 20 via the input / output device 26.

The CPU 21 sequentially stores this in a predetermined buffer set in the nonvolatile memory 24 or the RAM 23. The stored detection data of the force sensor 3 is used in software processing described later.

The ROM 22, the RAM 23 and the non-volatile memory 24, in addition to storing the detection data of the force sensor 3,
The program is used to store a program for controlling the operation of the robot control device 20 itself, a software process to be described later, a program for executing control of signal exchange with the signal processing device 20, and parameters related to each process.

The parameters to be set include the parameters related to the acceptance standard of the 6-axis force detected by the force sensor 3. Selection of acceptance criteria and parameters (a1, a2
.. a6, G0; b1, b2 ... b6, H0, etc.) is preferably set by screen input using an LCD attached to the teaching operation panel 25.

Based on the above matters, the outline of the software processing executed when the software safety joint is operated will be described with reference to the flowchart of FIG. This process is repeatedly executed in a short cycle when the robot operates. In addition to the process described in the flowchart of FIG. 3, a process of writing the data of the 6-axis force detected by the force sensor 3 in the buffer in a cycle that matches the above cycle (preferably the same cycle) is executed. Further, here, the above-mentioned [permissible standard 2] is adopted as the permissible standard of the 6-axis force detected by the force sensor 3, and the coefficients a1, a
2 ... The values of a6 and the allowable limit G0 have already been set.

First, in step S1, the latest data f1, f2, ... F6 representing the 6-axis force is read from the buffer, and in the subsequent step S2, the evaluation function g (f1,
f2 ... f6) = a1 | f1 | + a2 | f2 | + ...
-Calculate + a6 | f6 |.

Next, the calculated value of the evaluation function is compared with the permissible limit G0 in step S3. If the permissible limit G0 is exceeded, a robot stop signal is immediately output to stop the robot (step S4). ).

If such a process is repeatedly executed in a short cycle, when an interference occurs during execution of the jog feed or the regenerative operation for teaching using the arrangement shown in FIG. 1 (for example, the work 4). Even when the object collides with the work 5 or the table 6), the robot is stopped before a force sufficient to damage the robot mechanism or the works 4, 5 is applied, and further increase in external force is avoided. It

In order to make the response of the software safety joint at the time of interference as quick as possible, the response of the force sensor 3,
It is preferable that the processing time of the signal processing circuit 20, the writing cycle of the detection data into the buffer, and the processing cycle described in the flowchart of FIG. 3 are as short as possible. Force sensor 3
It is also advantageous from this point of view to determine whether it is safe or dangerous without converting the 6-axis force detected in step 6 into the 6-axis force acting on the tool.

The embodiment has been described above for the case where the acceptance criterion 2 is adopted for the robot used in the arrangement shown in FIG. 1, but the application to be applied is not particularly limited. For example, the software safety joint of the present invention can be effectively used as a means for avoiding a tool damage accident during deburring. As for the acceptance criteria for determining the safety / danger of the 6-axis force detected by the force sensor, other than the above-mentioned criteria are adopted as long as the magnitude of the 6-axis force detected can be roughly evaluated. It goes without saying that it does not matter.

It is rational to use a robot controller as a means for executing software processing for functioning the safety joint, as in this embodiment. It is also possible to share all or part of the required processing (for example, output of the maximum 6-axis force component, calculation of evaluation function, etc.).

[0038]

According to the present invention, by combining the force sensor and the simple software processing means, the joint itself is not destroyed and the safety joint effectively functions against impact force from multiple directions. Can be provided. Further, the software safety joint of the present invention has a characteristic that strength adjustment is easy. Therefore, by equipping the robot with the software safety joint of the present invention,
It is possible to improve the safety, efficiency and economical efficiency of work using a robot.

[Brief description of drawings]

FIG. 1 illustrates an arrangement for using a robot equipped with a software safety joint according to the present invention by taking a fitting application as an example.

2 is a block diagram showing an outline of a system used in the arrangement shown in FIG.

FIG. 3 is a flowchart outlining software processing executed when the software safety joint according to the embodiment is operated.

[Explanation of symbols]

 1 Robot Main Body 2 Robot Control Device 3 Force Sensor 4, 5 Work 11, 31 Cable 21 Central Processing Unit (CPU) 22 ROM 23 RAM 24 Nonvolatile Memory 25 Teaching Operation Panel 26 Input / Output Device 27 Robot Axis Control Unit 28 Servo Circuit 29 Bus 30 Signal Processing Device 41 Protrusion 51 Hole

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Claims (6)

[Claims] 1. A force sensor mounted between a tip of a wrist of a robot and a tool, software processing means, and software means for causing the software processing means to execute software processing related to an output signal of the force sensor. The software process includes a process for determining a relationship between the 6-axis force detected by the force sensor and a preset acceptance standard, and a process for ensuring safety according to the determination result. The processing includes the acceptance criterion, and the acceptance criterion is a vector <f> = (f1, f2 ... f having a component of the six-axis force detected by the force sensor.
6) Software safety fittings for robots that are set to roughly evaluate size. 2. A force sensor mounted between a tip of a wrist of a robot and a tool, and software processing means provided in a robot controller for controlling the robot,
The software processing means is provided with software means for executing software processing related to the output signal of the force sensor, and the software processing comprises the six-axis force detected by the force sensor and a preset acceptance criterion. The process includes a process for determining a relationship between the two and a process for ensuring safety according to the determination result, and the acceptance criterion is a vector having a component of the six-axis force detected by the force sensor. f> = (f1, f2 ... f
6) Software safety fittings for robots that are set to roughly evaluate size. 3. A force sensor mounted between the tip of the wrist of the robot and the tool, and software processing means provided in a robot controller for controlling the robot,
The software processing means is provided with software means for executing software processing related to the output signal of the force sensor, and the software processing comprises the six-axis force detected by the force sensor and a preset acceptance criterion. And a process for stopping the robot in accordance with the result of the determination, wherein the acceptance criterion is a vector having 6-axis force detected by the force sensor as a component. <F> = (f1, f2 ... f
6) Software safety fittings for robots that are set to roughly evaluate size. 4. The magnitude of each component of 6-axis force detected by the sensor is | f1 |, | f2 |.
.. The software safety joint of the robot according to claim 1, wherein allowable limits F1, F2, ... F6 for | f6 | are defined. 5. An evaluation function g (f1, f2 ... F6) = a1 | f in which the acceptance criterion has variables of respective components f1, f2 ... F6 of 6-axis force detected by the sensor as a variable.
1 │ + a2 │f2 │ + ・ ・ ・ ・ + a6 │f6 │ (however,
a1, a2 ... a6 are constants with the same sign)
The software safety joint of the robot according to any one of claims 1 to 3, wherein 6. An evaluation function h (f1, f2 ... F6) = b1 f1 ² whose variables are the respective components f1, f2, ... F6 of the six-axis force detected by the sensor.
+ B2 f2 ² + ... + b6 f6 ² (however, b1, b2 ...
The software safety joint of the robot according to any one of claims 1 to 3, wherein an allowable limit H0 of b6 is a constant having the same sign is predetermined.