Experimental results of using a step motor as a programmable spring

Often in "high level" robot motion planning the low level robot motion primitive is considered to be a programmable spring. Questions that arise are how to control an actual robot as a programmable spring and what are the performance limitations of such a programmable spring? One performance measure is the achievable dynamic range of programming the spring constant, i.e. the ratio of maximum to minimum programmable spring constants. In this paper it is shown how a variable reluctance step motor was controlled as a programmable spring with a spring constant that had a dynamic range of 2,000 to 1.