JP4022843B2 - Robot control method and control apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control method and a control device for a robot which is arranged on the machine side of a transfer device and performs a predetermined work on a work being transferred by the transfer device .
[0002]
[Prior art]
For example, as a control method for picking up a workpiece conveyed by a conveying device such as a belt conveyor with a robot, there is a method disclosed in Japanese Patent Laid-Open No. 60-217085. This is the following method.
A visual device is provided on a belt conveyor at a predetermined position on the upstream side with respect to the installation location of the robot, and the position, orientation, and speed of a workpiece conveyed on the belt conveyor by the visual device are measured, The position and orientation of the workpiece after a predetermined time (t seconds) is calculated from the measured position, orientation and speed of the workpiece, and control is performed so that the robot grasps the workpiece at the position after t seconds. .
[0003]
[Problems to be solved by the invention]
However, this conventional control method has the following problems. First, since the robot grabs the workpiece after a lapse of a predetermined time (t seconds) after the workpiece has passed under the visual device, depending on the robot arm position and posture conditions at the start of control, There is a problem that the workpiece cannot be moved to a position where the workpiece can be gripped in t seconds, and the workpiece cannot be gripped. Conversely, depending on the condition of the posture, the workpiece may be grasped at an earlier timing, but even in this case, the robot cannot grasp the workpiece until t seconds elapse. In other words, the robot schedule and the conveyor speed are determined in accordance with the worst conditions so as not to miss the workpiece, so that there is a problem that the efficiency of the robot operation is poor. Secondly, in this conventional control method, it is assumed that the conveyor moves at a constant speed from when the workpiece passes under the visual device until the robot grasps the workpiece, that is, after t seconds. Although it is a condition, because the moving speed of an actual conveyor changes due to slipping, etc., there is an error between the position after t seconds obtained by calculation and the actual position, and the workpiece cannot be grasped accurately. is there. Therefore, the present invention provides a robot control method and a control apparatus for controlling the robot so that the end effector of the robot can reach the workpiece being transported in the shortest time. Further, the present invention provides a robot control method and a control apparatus for correcting a robot operation according to fluctuations in the workpiece conveyance speed.
[0004]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a pivot shaft that rotates about a vertical axis with respect to an installation location, an arm that is mounted on the pivot shaft, and swings back and forth and up and down, and is attached to the tip of the arm. And an end effector that is rotatable about three orthogonal axes, and is disposed in the vicinity of a transfer device that transfers a workpiece, and performs a predetermined operation on the workpiece that is transferred by the transfer device And the rotational speed of the pivot axis is set to be equal to or lower than that of the three orthogonal axes and the axis that swings the arm back and forth and up and down, and the rotational angle of the pivot axis In a robot control method that is larger than the axis that swings back and forth and up and down and the three orthogonal axes, the conveyance speed of the conveyance device is measured, the position of the workpiece is measured, and the plane layout of the installation location Oh T seconds determined from an angle and an angular velocity of the arm with respect to the X axis in an orthogonal coordinate system in which the rotation axis of the robot is the origin and the axis parallel to the transfer direction of the transfer device is the X axis. An angle of the rear arm with respect to the X axis, and a rotation radius R assuming that the rotation radius of the reference point of the end effector about the turning axis after the t seconds in the orthogonal coordinate system is R ; the coordinate Et of t seconds the reference point after, the conveying speed and the coordinates at and from the reference point coordinates of the workpiece after t seconds in the orthogonal coordinate system obtained from the position of the workpiece obtained from A time t1 at which Et and the coordinate At of the workpiece coincide with each other and a coordinate Ab at that time are calculated, and the reference point of the end effector is directed to the coordinate Ab after t1 seconds. It is intended to operate the serial robot. In addition, the transport distance of the transport device is periodically measured, the point is calculated and corrected each time, and the end effector of the robot is operated toward the corrected point. Further, the position of the workpiece is measured using a visual sensor.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a plan view of a transfer device and a robot according to an embodiment of the present invention, FIG. 2 is a flowchart illustrating an embodiment of the present invention, and FIG. 3 is an explanatory diagram illustrating an image of a work captured by a visual sensor. FIG. 4 is an explanatory diagram for explaining coordinates based on the robot indicating the position of the workpiece to be conveyed. Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a conveying device such as a belt conveyor, which conveys the workpiece 2 from the left side to the right side in the drawing. Reference numeral 3 denotes an encoder which is attached to a drive shaft (not shown) of the transport device 1 and measures the rotation angle of the drive shaft. From the measured value of the encoder 3, the moving speed of the workpiece 2 on the conveying device 1, that is, the conveying speed, and the moving distance of the workpiece 2, that is, the conveying distance can be obtained. Reference numeral 4 denotes a robot that freely turns around a vertical axis S. The robot 4 includes an arm 4a that swings back and forth and up and down, and an end effector 5 is attached to the tip of the arm 4a so as to be rotatable around three orthogonal axes. Since it is configured in this manner, the robot 4 can take an arbitrary posture by rotating the vertical axis S and swinging the arm 4a back and forth and up and down. The direction and inclination of the end effector 5 can be arbitrarily determined by the rotation of the three orthogonal axes. Reference numeral 6 denotes a control panel of the robot 4. Further, the robot 4 is disposed on the machine side of the transport device 1 and grips the workpiece 2 transported on the transport device 1 with the end effector 5 and transports it to another device (not shown). A visual sensor 7 is arranged on the upstream side of the transport device 1 so as to look down at the transport device 1. Reference numeral 7 a denotes a visual field of the visual sensor 7. The visual sensor 7 is a device that, for example, combines a CCD camera and an image processing device, analyzes an image of the object captured by the CCD camera, and measures the position and orientation of the object. The signal lines of the visual sensor 7 and the encoder 3 are respectively connected to the control panel 6 of the robot.
[0006]
Next, a method for controlling the robot 4 will be described with reference to FIGS.
In FIG. 2, step S1 is a stage for calculating the transport speed of the transport apparatus 1, and the transfer speed V of the transport apparatus 1 is calculated from the output Ca of the encoder 3 at time ta and the output Cb of the encoder 3 at time tb. Obtained by the following equation.
[0007]
V = Kc * (Cb-Ca) / (tb-ta) (Formula 1)
[0008]
Here, Kc is a coefficient indicating the transfer distance of the transport device 1 per pulse of the encoder 3, and is a constant determined by the mechanical configuration of the transport device 1. When the work 2 enters the visual field 7a of the visual sensor 7, step S2 is executed. Step S2 is a stage for obtaining the position and posture of the workpiece 2. As shown in FIG. 3, the visual sensor 7 obtains coordinates G (X ₀ , Y ₀ ) of the center of gravity of the workpiece 2 based on the coordinate system fixed to the visual field 7 a of the visual sensor 7 based on the image of the workpiece 2. Also, an angle θ with respect to the normal posture of the work 2 is calculated.
In the next step S <b> 3, a position where the end effector 5 attached to the tip of the robot 4 grips the workpiece 2 is obtained. A point fixed to the end effector 5 and serving as a reference for alignment when the workpiece 2 is gripped is referred to as a reference point of the end effector 5. That is, if the direction of the end effector 5 is corrected by the angle θ and the reference point of the end effector 5 is made coincident with the center of gravity of the work 2, the end effector 5 can correctly grasp the work 2. In FIG. 4, in order to explain a method for obtaining the position where the workpiece 2 is gripped, the positional relationship among the transfer device 1, the workpiece 2, and the robot 4 is displayed in an orthogonal coordinate system with the turning axis S of the robot 4 as the origin. . In FIG. 4, the radius La and the radius Lb indicate the reach limit of the reference point of the end effector 5. That is, the reference point of the end effector 5 operates between the radius La and the radius Lb. Now, at the time of starting the control in step S3, the workpiece 2 is at a position indicated by coordinates Ao (p, q). The coordinate system used here is an orthogonal coordinate system in which the turning axis S of the robot 4 is the origin and the axis parallel to the transfer direction of the transport device 1 is the X axis. Since the visual sensor 7 is fixed with respect to the transfer device 1 and the robot 4, the coordinates of the workpiece 2 in the coordinate system fixed in the visual field 7a of the visual sensor 7 obtained in step S2 are converted into the orthogonal coordinate system. Is easy. Further, since the transport speed of the transport device 1 at this time is V obtained in step S1, the coordinates indicating the position of the work 2 after t seconds are obtained by At (p + V * t, q).
At the time of starting step S3, if the angle of the turning axis of the robot 1 is α and the angular velocity of the turning axis is ω, the angle of the turning axis after t seconds is α + ω * t. Here, assuming that the radius of rotation of the reference point of the end effector 6 around the turning axis S is R, the coordinates of the reference point of the end effector 6 are Et (R * cos (α + ω * t), R * sin (α + ω * t). ).
Since the point where the coordinates of the point A and the point E coincide is obtained, the following equation is obtained.
[0009]
p + V * t = R * cos (α + ω * t) (Formula 2)
[0010]
q = R * sin (α + ω * t) (Formula 3)
[0011]
Eliminating R from Equation 2 and Equation 3 yields:
[0012]
p + V * t = q / tan (α + ω * t) (Formula 4)
[0013]
If the solution of t obtained by solving Equation 4 is t1, the coordinates of the point where the workpiece 2 and the end effector 6 can meet in the shortest time can be obtained by Ab (p + V * t1, q). When the reference point of the end effector 5 is brought to this point, the rotation radius Rb around the turning axis S of the reference point is obtained by the following equation.
[0014]
Rb = q / sin (α + ω * t1) (Formula 5)
[0015]
Since the value of Rb is limited by the movement range of the robot 4, La <Rb <Lb must be satisfied. When Rb does not satisfy the condition of La <Rb <Lb, a signal is sent to an upper control device (not shown) as “abnormal” to execute a predetermined abnormality processing sequence.
Here, there remains a problem whether or not it is possible to operate each axis of the arm of the robot 1 during t1 seconds so that the end effector 6 can take a posture in which the turning radius around the turning axis S becomes Rb. In general, in a vertical articulated robot, the rotational speed of the turning axis is set to be equal or rather low compared to the swing axes of the arms. Further, the rotation angle of the turning shaft is larger than that of each swinging shaft of the arm. Therefore, when considering the problem of meeting the end effector 5 and the workpiece 2 in the shortest time, the operation time of the turning axis becomes a critical problem. In other words, in practice, if the movement of the pivot axis is in time, the movement of each swing axis of the arm can be considered to be in time.
In this way, the coordinates Ab and the time t1 at which the workpiece 2 and the end effector 5 can meet in the shortest time are determined, so that the reference point of the end effector 5 comes to the point Ab after 1 second after t1 seconds. Command. That is, an operation command with the point Ab as a movement target is given to the robot 4.
[0016]
Step S4 is a step of correcting the target of the operation of the end effector 5 by periodically measuring the transport distance of the transport device 1 after starting to move the end effector 5 toward the point Ab. Details of the control in step S4 are as follows.
When step S3 ends and the end effector 5 starts to move toward the point Ab, the output pulse CTm of the encoder 2 is periodically captured at a period of T seconds (where T <t1), and then measured at step S1. The correction amount ΔX of the target Ab is obtained by the following equation using the pulse value CTc at the same time calculated from the transfer speed V of the transport device 1.
[0017]
ΔX = (CTm−CTc) * Kc (Formula 6)
[0018]
Using this correction amount, the movement target of the end effector 5 is changed to Ab ′ (p + CV * t1 + ΔX, q). As described above, the transport distance of the transport device 1 is measured every cycle T seconds, compared with the transport distance obtained from the initially measured speed, and the movement target is corrected according to the difference.
The above calculation and control are performed by the control panel 6.
In the description of the embodiments, an example in which the present invention is applied to a robot that picks up and transfers a workpiece on a transfer device has been described. However, some work such as painting, gluing, and assembly is performed on the workpiece on the transfer device. Needless to say, the present invention can be applied to general robots for processing and the like. Further, the sensor for detecting the position and orientation of the workpiece is not limited to the visual sensor, but may be another type of sensor as long as it has a similar function.
[0019]
【The invention's effect】
As described above, according to the present invention, the robot is controlled so that the end effector meets the workpiece in the shortest time. Therefore, there is an effect that there is no waste in the operation of the robot and the efficiency of the robot operation is improved. In addition, since the movement target of the robot is corrected according to the change in the speed of the transfer device, there is an effect that the robot does not miss the workpiece.
[Brief description of the drawings]
FIG. 1 is a plan view of a transfer device and a robot according to an embodiment of the present invention.
FIG. 2 is a flowchart showing an embodiment of the present invention.
FIG. 3 is an explanatory diagram of an image of a work captured by a visual sensor.
FIG. 4 is an explanatory diagram for explaining coordinates on the basis of the transfer robot indicating the position of a workpiece to be transferred;
[Explanation of symbols]
1: Transfer device 2: Work 3: Encoder 4: Robot 4a: Arm 5: End effector 6: Control panel 7: Visual sensor 7a: Field of view of visual sensor

Claims (8)

A swivel shaft that rotates about a vertical axis with respect to the installation location, an arm that is mounted on the swivel shaft and swings back and forth and up and down, and an end that is rotatable about three orthogonal axes attached to the tip of the arm An effector, disposed in the vicinity of the transfer device for transferring the workpiece, and performing a predetermined operation on the workpiece being transferred by the transfer device, and the rotational speed of the pivot axis Is set to be equal to or lower than the axis that swings the arm back and forth and up and down and the three orthogonal axes, and the rotation angle of the pivot axis is orthogonal to the axis that swings the arm back and forth and up and down. In the robot control method, which is larger than the axis,
Measure the transport speed of the transport device,
Measure the position of the workpiece,
With respect to the X axis of the arm rotated by the pivot axis in an orthogonal coordinate system in which the pivot axis of the robot is the origin and the axis parallel to the transfer direction of the transfer device is the X axis in the plane layout of the installation location It is assumed that the angle of the arm with respect to the X axis after t seconds obtained from the angle and the angular velocity and the radius of rotation around the pivot axis of the reference point of the end effector after t seconds in the orthogonal coordinate system are R. rotation radius R, the coordinate Et of the reference point after the t seconds obtained from the coordinates at the workpiece after t seconds in the orthogonal coordinate system obtained from the position of the said transport speed workpiece when , The time t1 when the coordinate Et of the reference point and the coordinate At of the workpiece coincide with each other and a coordinate Ab at that time are calculated.
A robot control method, wherein the robot is operated such that a reference point of the end effector is directed to the coordinate Ab after t1 seconds.    The fluctuation of the conveying speed of the conveying device is periodically measured, the point is calculated and corrected each time, and the robot is operated so as to go to the point corrected by the end effector. Item 2. A robot control method according to Item 1.   The robot control method according to claim 1, wherein the position of the workpiece is measured using a visual sensor.   The robot control method according to any one of claims 1 to 3, wherein the transport speed of the transport device is measured using an encoder connected to a drive shaft of the transport device. A swivel shaft that rotates about a vertical axis with respect to the installation location, an arm that is mounted on the swivel shaft and swings back and forth and up and down, and an end that is rotatable about three orthogonal axes attached to the tip of the arm An effector, disposed in the vicinity of the transfer device for transferring the workpiece, and performing a predetermined operation on the workpiece being transferred by the transfer device, and the rotational speed of the pivot axis Is set to be equal to or lower than the axis that swings the arm back and forth and up and down and the three orthogonal axes, and the rotation angle of the pivot axis is orthogonal to the axis that swings the arm back and forth and up and down. In a robot control device that is larger than the axis,
Measure the transport speed of the transport device,
Measure the position of the workpiece,
With respect to the X axis of the arm rotated by the pivot axis in an orthogonal coordinate system in which the pivot axis of the robot is the origin and the axis parallel to the transfer direction of the transfer device is the X axis in the plane layout of the installation location It is assumed that the angle of the arm with respect to the X axis after t seconds obtained from the angle and the angular velocity and the radius of rotation around the pivot axis of the reference point of the end effector after t seconds in the orthogonal coordinate system are R. rotation radius R, the coordinate Et of the reference point after the t seconds obtained from the coordinates at the workpiece after t seconds in the orthogonal coordinate system obtained from the position of the said transport speed workpiece when , The time t1 when the coordinate Et of the reference point and the coordinate At of the workpiece coincide with each other and a coordinate Ab at that time are calculated.
The robot control apparatus, wherein the robot is operated so that a reference point of the end effector is directed to the coordinate Ab after t1 seconds.   The fluctuation of the conveying speed of the conveying device is periodically measured, the point is calculated and corrected each time, and the robot is operated so as to go to the point corrected by the end effector. Item 6. The robot control device according to Item 5.   The robot control apparatus according to claim 5, wherein the position of the workpiece is measured using a visual sensor.   The robot control device according to claim 5, wherein the transport speed of the transport device is measured using an encoder connected to a drive shaft of the transport device.

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