JPH01103277A - Method of controlling position of origin of robot arm - Google Patents

Abstract

PURPOSE: To prevent a runaway of an arm and damage and the like in a workpiece by automatically measuring a pulse number of a pulse generating means arranged in a motor from just after the actuation of an origin limit switch installed to the robot arm until just before generation of zero-pulse of a servomotor, comparing the pulse number with a set value, and returning the arm to the origin position. CONSTITUTION: In detection of an origin position of a robot arm 10 by means of an origin limit switch 14, a zero-pulse generating means and a continuous pulse generating means 30 are arranged in a servomotor 22 driving the robot arm. From just after the actuation of the origin limit switch 14 until an appearance of the next zero-pulse Po , a number of pulses obtained from the continuous pulse generating means 30 is counted. Then, the counted pulse number is compared with a reference pulse number showing that the robot arm is in the accurate origin position, so that it is determined whether the robot arm 10 is in the accurate origin position or not. If the robot arm 10 is not placed in the accurate origin position, the robot arm 10 is returned to the origin position, and a runaway of the robot arm 10 can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling the origin position of a robot arm.
- Layer In detail, when detecting the origin position of the robot arm (the position related to the robot's starting point of operation) using a limit switch, etc., a rotary encoder is provided on the servo motor that substantially drives the robot arm, The number of pulses is counted during the period from immediately after the limit switch is activated until the next output pulse of the rotary encoder appears, and the number of pulses is compared with the number of pulses indicating a predetermined origin position. The present invention relates to a method for controlling the origin position of a robot arm, which makes it possible to control the position of the robot arm by determining whether or not the robot arm is at the correct origin position.

[Background of the Invention] A conventional method for controlling the origin position of a robot arm is to arrange a rotary encoder coaxially with a servo motor that essentially drives the robot arm, and to use a rack function as the drive shaft of the robot arm. A limit switch is provided to be engaged with the rack having a rack, and the position where a zero pulse is first generated after the limit switch is closed is determined as the control origin position. When the robot is used, the moving distance of the robot arm is controlled by counting the number of consecutive pulses after the zero pulse is generated, thereby controlling the position of the robot arm as a whole.

However, in the conventional method for controlling the origin position of the robot arm described above, the period from when the origin limit switch closes until the arrival of the first zero point pulse is not monitored. If there is a positional deviation of the origin limit switch drive mechanism, the origin position of the robot arm will not match the correct control origin. As a result, for example, there is a risk that an error may occur in the transport position of the workpiece, resulting in damage to the workpiece or an unexpected runaway accident due to positional deviation of the robot arm.

On the other hand, when performing such a return-to-origin operation, if the robot uses an incremental type detector,
It is necessary to ensure the home position by returning to the home position when the power is turned on. In this case, a method is adopted in which all the drive axes of the robot are returned to the origin at the same time, or each drive axle is returned to the origin in a specified order.

However, according to this method, since the robot returns to its origin no matter what operating range it is in, interference with peripheral devices may occur.

[Object of the Invention] The present invention has been made in order to overcome the above-mentioned disadvantages, and when detecting the origin position of the robot arm using a limit switch etc. attached to the robot arm, the robot arm is A rotary encoder is arranged on the servo motor that drives the limit switch, and all the origin limit switches are set to 0 by the mechanism that drives the limit switch.
The origin position of the robot arm is detected by counting the number of pulses output during the period from immediately after operation in the N state until the next output pulse of the rotary encoder is generated, and the origin position is determined relative to the robot arm. Automatically determines whether or not it is at the correct predetermined origin position,
As a result, it is an object of the present invention to provide a method for controlling the origin position of a robot arm, which makes it possible to avoid runaway of the robot arm and also prevent damage to the workpiece.

[Means for Achieving the Object] In order to achieve the above object, the present invention comprises a robot arm operated by a plurality of drive axes, a drive source, and an incremental encoder disposed corresponding to the drive source. When performing control using an output signal, the origin positions of the plurality of drive axes are detected using an origin limit switch, and the robot arm is controlled to return to the origin position when each origin limit switch is in an ON state. shall be.

Furthermore, when the present invention detects the origin position of the robot arm using an origin limit switch or the like, the servo motor that substantially drives the robot arm is provided with zero pulse generation means and continuous pulse generation means, and the origin limit The number of pulses obtained from the continuous pulse generation means is counted during the period from immediately after the switch operates until the next zero pulse appears, and then the number of pulses is compared with the reference number of pulses that indicates that the home position is correct. By doing so, it is determined whether or not the robot arm is at the correct origin position.

[Embodiments] Next, the method for controlling the origin position of a robot arm according to the present invention will be described in detail below with reference to the attached drawings, citing preferred embodiments in relation to a device for implementing the method. .

FIG. 1 schematically shows the configuration of an apparatus for carrying out the present invention, in which reference numeral 10 indicates a robot arm. A robot manipulator (not shown) is attached to the tip of the robot arm IO. Further, an origin limit switch driving member 1 is provided near the end of the robot arm 10.
2 is attached. In this case, the origin limit switch 14 is configured to operate when the origin limit switch driving member 12 moves to a predetermined position together with the robot arm 10. The output signal of the origin limit switch 14 is sent to an input/output interface (Ilo IF) in the robot control circuit 16, the details of which will be described later.
)1B.

Meanwhile, a rack mechanism 20 is attached to the robot arm 10. That is, a reducer 24 is engaged with the servo motor 22 that drives the robot arm 10, and a pinion mechanism 26 fitted into the rotating shaft 25 of the reducer 24 and the rack mechanism 20 mesh with each other.

A rotary encoder 30 is disposed on the servo motor 22 , and the zero pulse output of the rotary encoder 30 is introduced into the input/output interface 18 in the control circuit 16 . Further, the servo motor 22 is driven by a servo motor drive circuit 28 disposed within the control circuit 16. A rotary encoder 30 is attached to the rotating shaft 25 of the servo motor 22, and the output pulse signal of the rotary encoder 30 is transmitted to the control circuit 1.
input/output interface 18 in 6.

Note that the control circuit 16d includes a CPU 32, a ROM 34,
RAM 36, counter 38, input/output interface 18
are connected to each other by a pass line, and the servo motor drive circuit 28 described above is provided, and the servo motor drive circuit 28 is drive-controlled by the CPU 32 via the input/output interface 18.

The device for carrying out the method for controlling the origin position of a robot arm according to this embodiment is basically configured as described above, and its operation and effects will be explained next.

FIG. 2 is a part of a flowchart of a program stored in the ROM 34 incorporated in the control circuit 16 to implement the present invention.

Therefore, now that the assembly of the robot is completed, first, the initial origin of the robot arm 10 is set (STPI).

In this case, the origin limit switch driving member 12 is attached to the robot arm 10 so that the manipulator (not shown) attached to the tip of the robot arm 10 is in an appropriate position relative to the workpiece (not shown). . At this time, when the robot arm 10 moves in the direction A in FIG. 1 and reaches point B in the figure, the origin limit switch drive member 12 contacts the origin limit switch 14, causing the contact of the origin limit switch 14 to is closed, and the origin limit switch operation signal shown in FIG.
is introduced into the CPU 32 through the CPU 32.

By the origin limit switch operation signal, the CPU 32
The counter 38 connected to is reset and its count number is set to zero. Then, when the robot arm IO is further conveyed in the direction A, the pulse signal shown in FIG.
2 is input to the CPU 32 via the input/output interface 18. The number of pulses is counted by the counter 38. Then, when the robot arm 10 further advances in the direction A and reaches a predetermined position, a zero pulse P0 shown in FIG.

When the zero pulse is introduced into the CPU 32 through the input/output interface 18, the CPU 32 brakes the servo motor through the input/output interface 18 and the servo motor drive circuit 28, and stops the counter 38 from counting pulses. Then, the number of pulses N (in this case, N=5) in the t interval (see FIG. 3) counted by the twenty counter 38 is stored in the RAM 36.

Through the above operations, the initial origin of the robot is set.

Then, the robot arm 10 is moved in a direction opposite to the direction A in FIG. 1 in order to perform a predetermined machining operation on the workpiece. When the predetermined work is completed, the robot arm 10 is moved at high speed in the A direction to return to the original position (SrF2).

Then, during this operation, the origin limit switch 1
4 is closed (SrF3).

In this judgment, if the origin limit switch 14
If it is not closed, the process returns to step 2 again and the robot is moved at high speed in the A direction to return to the origin. If the origin limit switch 14 closes and goes out, the number of output pulses of the rotary encoder 30 (the number of pulses after point B in FIG. 3a)
Start counting (SrF2).

Therefore, at the same time as starting to count the number of pulses after point B, the robot arm IO is moved at low speed in the incoming direction (Sr
F2). This low-speed movement is a measure to ensure that the counter 38 performs its operation, that is, to eliminate counting errors and to reduce positional deviation due to inertial force during braking of the servo motor 22 and reducer 24. It is. Therefore, if there are no problems with these two points, there is no need to operate at a particularly low speed.

Even during this low-speed operation, the rotary encoder 3
The number of zero pulses is counted and a detection judgment is made as to whether or not a zero pulse has occurred (SrF2).

If a zero pulse is not generated, the process returns to step 5 and the robot arm 10 continues to move at low speed. If a zero pulse is generated, proceed to the next step 7.

In step 7, when the CPU 32 detects and determines a zero pulse, the CPU 32 immediately sends a servo motor braking signal to the servo motor 22 via the servo motor drive circuit 28 to stop the servo motor 22 by braking. As a result, the robot arm stops (SrF2).

The CPU 32 generates the servo motor drive signal and at the same time obtains the result of counting the number of pulses from the rotary encoder 30 from the counter 38. At this time,
Stop counting the pulses of the counter 38 (SrF2)
.

Here, the CPU 32 compares the pulse count value with the pulse count value N at the time of initial setting of the origin position obtained in step 1 (SrF9).

If the comparison result is not the same, the CPU 32 drives a buzzer and/or lamp (not shown) to notify the operator that an error has occurred. and,
When the operator receives the alarm from the buzzer and/or lamp, the operator shall stop the robot and perform error handling (STPIO).

If the numbers are the same, the CPU 32 determines that the return to origin is normal and ends the return to origin operation (E
N.D.).

[Effects of the Invention] As described above, according to the present invention, the pulse of the rotary encoder attached to the servo motor is controlled immediately after the origin limit switch attached to the robot arm is activated until immediately before the zero pulse of the servo motor is generated. By automatically measuring the number of pulses and comparing the number of pulses with a predetermined number of pulses, the correct origin position of the robot arm can be determined at all times, making it possible to prevent runaway of the robot arm and damage to the workpiece. The effect of this can be obtained.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
For example, in the present invention, the opening/closing state of the origin limit switch is configured to be memorized by the CPU.
- For robots with the above origin limit switches, i.e., multi-axis robots, the ROM is configured so that the robot returns to origin only when all origin limit switches of each axis are closed. The gist of the present invention is that the ROM program can be modified to start the return to origin only when the origin limit switch of only the selected axis is closed, if necessary. It goes without saying that improvements in the species and changes in design are possible within a range that does not deviate from the above.

[Brief Description of the Drawings] Fig. 1 is a block diagram of an apparatus for implementing the method of the present invention, Fig. 2 is a flowchart for implementing the method of the present invention, and Fig. 3 is a diagram of an apparatus for implementing the method of the present invention. FIG. 3 is a waveform diagram illustrating the operation. DESCRIPTION OF SYMBOLS 10... Robot arm 12... Origin limit switch drive member 14... Origin limit switch 16... Control circuit 20... Rack mechanism 22... Servo motor 26... Binion mechanism 28... Servo motor drive circuit 30...rotary encoder 32...CPU34...
...ROM 36...RAM38...
·counter

Claims (3)

[Claims] (1) When a robot arm operated by multiple drive axes is controlled by a drive source and the output signal of an incremental encoder installed corresponding to this drive source, the origin position of the multiple drive axes is set to the origin limit. A method for controlling the origin position of a robot arm, comprising detecting the origin using a switch, and controlling the robot arm to return to the origin position when each origin limit switch is in an ON state. (2) When detecting the origin position of the robot arm using an origin limit switch or the like, the servo motor that substantially drives the robot arm is provided with zero pulse generation means and continuous pulse generation means, and the origin limit switch is activated. Count the number of pulses obtained from the continuous pulse generation means during the period from immediately after that until the next zero pulse appears,
Control of the origin position of a robot arm, characterized in that it is determined whether or not the robot arm is at the correct origin position by comparing the number of pulses with a reference pulse number indicating that the robot arm is at the correct origin position. Method. (3) A method for controlling the origin position of a robot arm according to claim 2, wherein the zero pulse generating means and the continuous pulse generating means are comprised of rotary encoders.