The invention relates to a device for displacing an object, which device includes a drive device for moving the object along an axis of motion, a control unit which is coupled to the drive device, a set-point generator which is coupled to the control unit and is arranged to determine from secondary conditions a jerk set profile and set points for a plurality of sampling periods for a trajectory to be traveled and to apply the set points to the control unit per sampling period. A problem solved by the invention consists in that secondary conditions such as, for example the maximum velocity or the desired final position, can be changed during a motion along a trajectory. To this end, during the displacement along the trajectory and in response to a change of the secondary conditions, a jerk set profile and associated set points are derived in the set-point generator from the secondary conditions for the sampling periods as from a sampling period succeeding the change. A jerk set profile is used which comprises two pulse pairs, each pulse pair comprising two pulses of the same amplitude and opposite sign. It is an advantage of the invention that the waiting time for the execution of changed instructions is reduced.
Acceleration/deceleration control is performed on the basis of a designated jerk control such that a maximum absolute value Jmax of jerk value, which is differential value of acceleration, is made not larger than a predetermined value when a commanded quantity of servomotor movement is smaller than a minimum quantity Smin of motor movement which is required to allow the movement of the servomotor to reach a predetermined maximum velocity Vmax and a predetermined maximum acceleration Amax.
Control of time-dependent states, such motion, is facilitated in a manner that avoids explicit solution to the governing equations, but which permits specification of both an initial and a final acceleration. This permits the operator to restrict jerk by exerting control over the final acceleration (e.g., by setting this equal to the initial acceleration, or constraining it to within an allowed maximum), but without explicitly computing parameter values for jerk. More generally, the approach is useful in controlling any system in which states evolve with respect to a specific parameter (frequently, but not necessarily, time), and whose evolution can be described by a defined set of algebraic equations.
A method of controlling a motor comprises providing a motion control system and causing the shaft of the motor to move from an initial state to a new state, such as from an initial position or velocity to a new position or velocity. Coefficients for each of a plurality of polynomial segments of a motion profile are determined. The plurality of polynomial segments and the corresponding coefficients for each respective segment characterize planned movement of the shaft through each respective segment. In a particularly preferred aspect, each segment is defined by a plurality of polynomials, which include a first polynomial that describes shaft position with respect to time, a second polynomial that describes shaft velocity with respect to time, and a third polynomial that describes shaft acceleration with respect to time. The shaft of the motor is then controlled, using a motion control loop, based on reference values generated using the plurality of polynomial segments and the corresponding coefficients for each respective segment.
By moving supports A and C along respective tracks (3) and (4), the free end B of robot arm (2), with gripper (5), is caused to move along a path P, the locus of which may be varied by varying the movements of the supports A and C. Motors (6) and (7) are not carried on the robot arm (2), but are secured to the frame (10) of the device (1). The robot arm (2) may thus have very low mass, resulting in very high performance in terms of speed and efficiency. The path P may comprise a NURB curve, and the time-distance function of motion of end B of arm (2) along path P may comprise a polynomial function having first and second derivative (velocity and acceleration) continuous curves.
