Flexible, High-Performance Motion Trajectories
Almost all machines that use ControlPoint have at least a few motion control requirements. For most machines, the motion is of fundamental importance. The path that a motion axis follows when moving from one point to another— its trajectory—is critical in determining the quality of the motion. The trajectory affects the smoothness, the throughput, the dynamic tracking accuracy, the sound and vibration, and the power utilization of the motor and servo drive (and hence their size and cost). The actual trajectory that is followed is a function of two things: the commanded trajectory and the tracking accuracy (i.e., the ability of an axis to closely track its command). The actual trajectory can only be as good as the commanded trajectory, so let's consider the quality of ControlPoint's trajectory generation.
Smooth motion starts with smooth motion trajectories. The commonly used trapezoidal move profile, with its abrupt velocity transitions, is analogous to putting octagonal wheels on a car. Instantaneous transitions in the move command are impossible for even a perfect motion system to follow and cause vibration, resonances, excessive motor heating, tracking errors and increased mechanical wear. Some control systems attempt to improve on the common trapezoidal move trajectory by applying a jerk limitation. This is a limit on the rate of change of acceleration. This is very beneficial, but misses an important point: this still allows for discontinuous changes in acceleration. For example, the transition between zero acceleration and the acceleration ramp will still happen abruptly. This is because in the jerk-limited trajectory, the time-derivative of the jerk is not limited. This causes excess noise, vibration and heat. Further, since power is wasted, bigger, more expensive motors and drives must be used.
Teknic ControlPoint trajectories all have the capability of having their jerk derivative limited, something we colloquially refer to as "double jerk limiting." (This feature expands on the proprietary Regressive Auto-Spline feature introduced several years ago on Teknic servo drives for improving the trajectories of servo controllers.) This double jerk limiting has the effect of making all commanded changes in acceleration happen smoothly. This allows for extremely smooth, cam-like motion. Furthermore, if the acceleration is smooth, the peak torque requirements will be lower, thus allowing faster overall accelerations. Settling time at the ends of moves will also be faster. This is the best of all worlds— smoother and faster motion.
Additionally, for maximum performance, any of these profiles can be easily double jerk limited, to a user-definable degree, just like the basic trapezoidal trajectories.
For further flexibility, any trajectory can be configured to signal when it reaches a certain point after its start or before its end. This feature is very useful for synchronizing moves or triggering external devices such as cameras. Multiple moves can be synchronized to start simultaneously using the "group Go" command, and the ends of moves can be precisely determined using "move idle" and configurable "move done" status indicators.
ControlPoint offers an extremely flexible and easy to use array of motion trajectory features to achieve the smoothest, highest performance motion available today.