Issue link: https://resources.mouser.com/i/1442757
22 position (Figure 6). Higher rates might speed up the entire positioning cycle, but they might also induce sudden changes in acceleration motion, called the jerk, which, in turn, adds to inaccuracy and overshoot. • The S-curve, a frequently-used enhancement to the trapezoid, where the acceleration rate ramps up from zero, then decreases as the target velocity is achieved (Figure 7). Then, as the target position is reached, the deceleration rate is ramped up and then reduced as the endpoint is near. The S-curve actually has seven distinct phases, in contrast to the three phases of the trapezoid. • In contoured motion, the user establishes a set of desired positions, and the motion controller directs a smooth, jerk-free transition prole through all of these points (Figure 8). This allows the ultimate in exibility and control, which is necessary for advanced motion situations. The required calculations of control directions to achieve smooth curve-tting are complex and must be accomplished without loss of resolution due to rounding or truncation errors, despite the many calculations. Figure 6: The simplest motion-trajectory profile is the trapezoid, which has constant acceleration to the target velocity, constant path velocity, and constant deceleration between start and endpoints. (Source: Performance Motion Devices) Figure 7: The S-curve path is more complicated than the basic trapezoid, but it eases the jerk (change in acceleration) at each transition point of the path. (Source: Performance Motion Devices) Figure 8: The contoured-motion path allows the user to dene a series of position marker points between starting and ending points, and the controller must guide the end-effecter through these in a smooth curve. (Source: National Instruments) There are other proles in use, some of which are associated with specic application groups or industries. Regardless of the desired prole, it's one thing to want it and another to make it happen. The well-known, highly effective Proportional-Integral- Derivative (PID) closed-loop control algorithm is the most common approach used to drive the motor and end-effector to do what is wanted with high enough accuracy and precision (Reference 1). Effective control of a single axis is a manageable project, but robotic control becomes far more difcult when this control extends to two, three, or more motors and degrees of freedom, which must be closely coordinated and synchronized with the performance along one dependent on the status of the others. Determining Standard Versus Custom Motion Control Applications For standard motion control applications, a dedicated, xed- function, embedded controller Integrated Circuit (IC) offers ease of use and rapid time-to-market. In contrast, if a non-standard, customized prole is needed or if the correlation between the various axes is complicated and must accommodate unusual or unique events, then the design team may consider a fully user-programmable processor. This solution is implemented with a processor with Digital Signal Processor (DSP) capabilities for the computation-intensive aspects or with a Field-Programmable Gate Array (FPGA). When considering programmable devices, Reference: IEEE GlobalSpec Electronics360, "Proportional Closed-Loop Control: The Foundation of Automated Systems"