A polynomial-based trajectory generator for improved telescope control

摘要

For any telescope, a fundamental performance requirement is the acquisition and tracking of the source. While this depends on many factors, the system accuracy is fundamentally limited by the servo tracking perfor-mance on the encoders. This tracking performance must be balanced with the need for large slewing motions to new sources. While the classical rate loop and position loop model permits basic operation, there has been increasing use through the years of gain scheduling or command pre-processors to improve telescope path plan-ning and enable better performance. This is particularly important for telescopes that employ scanning or fast switching motions. As telescope control systems have moved to fully digital systems running at high update rates, more sophis-ticated approaches have become possible for telescope path planning. Taking advantage of the speed of available computation, we have developed a new real time trajectory generator that provides improved performance over previous implementations. Given a position command, the system generates a path to the desired end point. The resulting path is guaranteed to be continuous in position, velocity, and acceleration, as well as to respect specified limits in velocity, acceleration, and jerk. Significantly, the calculation provides not only the desired position over the interval, but also the velocity and acceleration, permitting their use in feedforward control to improve the tracking accuracy at all points on the path. The algorithm is presented, as well as some results with the system implemented on a real telescope.