Introduction to MOTOMAN robot motion control instructions

Introduction to Yaskawa Coordinate System

The figure above shows the six-joint MOTOMAN, which consists of waist joint S, upper arm joint L, lower arm joint U and wrist joints R, B, T. Therefore, the spatial position of the robot end effector can be expressed as P (S, L, U, R, B, T), where S, L, U, R, B, T are the coordinates of each joint of the robot at this position relative to the joint zero point. In addition, in the rectangular coordinate system, the position P can also be expressed as P (X, Y, Z, TX, TY, TZ), where X, Y, Z represent the position of point P, and TX, TY, TZ represent the posture of point P.

There are four internal coordinate systems in MOTOMAN: joint coordinate system, robot coordinate system, base coordinate system and user coordinate system. The latter three are rectangular coordinate systems. The points saved during the teaching process are all expressed in joint coordinates. Users can establish their own user coordinate system inside the robot. After teaching, use internal instructions to convert the teaching file (Specified job) into a relative file (Related job) in the user coordinate system, so that the coordinates of the teaching point in the user coordinate system can be obtained. In this way, it is very convenient to do some processing in the user coordinate system.

Introduction to MOTOMAN robot motion control instructions

1. Point To Point Control (PTP control)

This method only controls the position and posture of the robot operator's starting point and the target point to be reached, but does not control the motion trajectory from the starting point to the target point. Its characteristics are: only guaranteeing the position and posture accuracy of a limited number of intermediate points and the end point, simple control method, and fast movement speed. Robots using this motion control method are mostly used for operations such as spot welding, material handling, and robot idle travel motion.

2. Continuous Path Control (CP Control)

This method is controlled according to the motion trajectory of continuous motion. The robot can achieve smooth and correct motion at a specified speed and on a specified route. Its characteristics are: it can ensure the position accuracy of each point on the planned path, and the motion is smooth, but the control method is relatively complex. Robots using this motion control method are mostly used for operations such as arc welding and cutting.

For the MOTOMAN six-joint welding robot, it mainly adopts PTP control and CP control. Its internal robot motion instructions are mainly:

1. MOVJ (Joint Movement)

This command belongs to point control. It only controls the precise position and posture of the starting point and the target point, and does not care about the actual path during the movement. During the movement, the motors of each joint start and stop at the same time. It is usually used for idle travel movement when adjusting the position.

2. MOVL (Motion in Linear Direction)

This command belongs to continuous trajectory control, which realizes linear movement from point to point. It determines the position of the middle point by linear interpolation between two points, thereby achieving precise linear motion.

3. MOVC (circular motion)

This command belongs to continuous trajectory control. First, circular interpolation is performed on the three points of spatial teaching to fit the trajectory of the robot's circular motion, and then continuous position control of the robot is achieved based on the trajectory.

Inside the MOTOMAN robot, the format used for motion control is usually:

MOV* PT, V

Among them, MOV* represents MOVJ, MOVL, MOVC, PT represents the corresponding robot teaching point, and V represents the average speed of the robot movement.

Summarize

The experience of using MOTOMAN robots shows that the execution of MOVL instructions is completed within the nominal time (the nominal time is calculated based on the distance between two points and the nominal speed, =ts/v), which means that the acceleration, uniform speed and deceleration during the entire execution of MOVL instructions are completed within the nominal time. And when executing two MOVL instructions, the speed smoothing between segments does not affect the actual execution time equal to the nominal time. This makes it possible to control the positioner and robot movements separately according to the nominal time to achieve coordinated operation. In the subsequent arc coordinated welding, the welding trajectory of the robot is fitted with a small line segment, and then the nominal time is calculated according to the set nominal speed. Finally, the positioner movement is controlled according to the nominal time, thereby achieving the unification of time with the robot.

Editor: Huang Fei