Basic Robot-Motion Parameters Basic Robot-Motion Parameters When programming a robot, there are several factors that play an important part in performance. In order to achieve optimum performance from your robot, it is helpful to have an understanding of how these factors work. Speed, Acceleration, and Deceleration Robot speed is usually specified as a percentage of normal speed, not as an absolute velocity. The speed for a single robot motion is set in the Speed parameter of the Pick Motion Parameters or Place Motion Para- meters dialogs for each Part or Part Target location.
Note that the result obtained by the speed value depends on the operating mode of the robot—joint-interpolated versus straight-line (for details, see Joint- Interpolated Motion vs. Straight-Line Motion on page 64). Whether in joint-interpolated mode or straight- line mode, the maximum speed is gated by the slowest-moving joint during the motion, since all the joints are required to start and stop at the same time. For example, if a given motion requires that the tool tip is rotated during the motion, which requires Joint 4 to rotate, that joint could gate the maximum speed achieved by the other joints, since Joint 4 is the slowest-moving joint in the mechanism.
Using the same example, if Joint 4 was not rotated, the motion could be faster without any change to the speed value. NOTE: The motion speed specified in the Pick Motion Parameters or Place Motion Parameters dialogs must always be greater than zero for a regular robot motion. Otherwise, an error will be returned. You can use the Acceleration parameter to control the rate at which the robot reaches its designated speed and stops. Like speed, the acceleration/deceleration rate is specified as a percentage of the normal accel- eration/deceleration rate.
To make the robot start or stop smoothly (using lower acceleration and decel- eration for a less-abrupt motion), set the Acceleration parameter to a lower value. To make the robot start or stop quickly (using higher acceleration and deceleration for a more-abrupt motion), set the Acceleration parameter to higher values. The Speed and Acceleration parameters are commonly modified for cycle-time optimization and process constraints. For instance, abrupt stops with a vacuum gripper may cause the part being held to shift on the gripper. This problem could be solved by lowering the robot speed. However, the overall cycle time would then be increased.
An alternative is to slow down the acceleration/deceleration rate so the part does not shift on the gripper during motion start or stop. The robot can still move at the maximum designated speed for other movements. Another case would be a relatively high payload and inertia coupled with tight pos- itioning tolerances. A high deceleration rate may cause overshoot and increase settling time. Higher accel- eration/deceleration rates and higher speeds don't necessarily result in faster cycle times. Approach and Depart Approach and depart heights are typically specified for pick and place locations. The Approach Segment parameters are shown in the following figure:
ACE User's Guide, 3.6.x, 18316-000 Rev A Page 61