Multiple Point Robot Movements

Pick and place applications are common in robotics. Read this paper to learn how to blend multiple robot move commnands with the ImagingLab Robotics Library for DENSO to create pick and place movements and other blended motions.

Background

This paper is part of the ImagingLab Robotics Library for DENSO Reference Guide.  The paper assumes you are familiar with the setup, initialization, and basic movement commands of the DENSO robot from LabVIEW.  For a review on these topics and an introduction to the library, follow the preceding link to the reference guide.

Multiple-Point Moves

Executing multiple move robot commands in a row queues the movements on the robot controller and allows for movements to be blended together to produce a smooth path between positions. This type of blending is particularly useful in pick and place applications, which move the robot to a location to pick up a part and then to another location to place the part in an assembly or other destination.

Pick and Place

In typical pick and place applications, the robot does not move directly to the pick or place location but instead moves from some offset position above the part. This keeps the end effector from knocking over or damaging parts while moving into position and allows the placement of the part to be inside some walled location. To perform these types of movements, use the Approach, Move, and Depart VIs. The Approach and Move VIs use the same target position, but Approach has an input for the approach distance, or offset from the part. Once at this approach position, the Move VI is called to move to the exact target position, and, after operating the end effector, the Depart VI is used to return to the offset position before proceeding to the next location.

Movement Parameters

Interpolation

 A required input for each movement VI is the motion parameters cluster. The inputs in this cluster specify the interpolation, pass motion, and move option. The interpolation affects the path taken between two positions. Move P is the default interpolation type and, when selected, the robot takes the most efficient path to the next location. Move L requires the end effector to move in a linear path to the next location. This is useful for instances when the part to be handled needs to be lifted straight up or pass through a channel en route to the next position. It is important to note, however, that when using linear interpolation, the path between the two points must be a valid space for the robot to travel. For instance, you cannot perform a linear move from one side of the robot to the other because it requires the robot to move through itself.

Pass Motion

The second input in the cluster specifies the pass motion to be used with the movement. A pass motion determines the motion for arriving at the final position. @0, known as the default value, stops the robot when the command value of the servo system meets the destination position. You can use this pass motion not only for movements to an end position but also as a pass through position that needs to be reached within a certain deviation. Another method of passing through a position is a pass motion of @P, which you can use to blend between the current movement and the next movement. Using @P causes the current movement to end at some distance away from the target position so it can pass through that position en route to the next position. Much like using the default value of @0, using @E stops the movement at the target position, but @E uses the encoder value to stop the motion when the motor reaches the destination position at its corresponding encoder value. This is the best method to implement to arrive at exactly the target position.

Move Option

The last parameter is the Move Option, which has values of Default and Next. When you select Default, the current movement the robot is performing must fully reach its end position before the robot proceeds to the next movement. When you select Next, the robot proceeds to the next movement instruction without waiting for the movement to fully complete. This creates a blending effect between the two movements. Approach and Depart moves are usually executed with Next as the Move Option because the offset positions are often not the end movement and it is not essential for these movements to be fully completed or for the robot to be brought to a stop before proceeding to the next move.

Next Step

Continue on to the following paper to learn how you can calibrate a vision and robot system to create a vision-guided robotics application using the ImagingLab Robotics Library for DENSO.

>> Vision Guided Robotics

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