FHA-C Series - Harmonic Drive LLC

Chapter 2 Guidelines for sizing2-4-5 Calculating equivalent dutySpeedThe load conditions, which is torque, speed, moment of inertia,acceleration/deceleration time, loading time, are limited by theactuator to drive the load. To select the proper actuator, theequivalent duty of the load should be calculated.The %ED (percent equivalent duty) is:Nta tr td tst: duty cycleTime%ED = Kla x ta + Klr x tr + Kld x td x 100twhere, ta: acceleration time in secondtd: deceleration time in secondtr: driving time in secondt: single cycle time in secondKla: duty factor for acceleration timeKlr: duty factor for driving timeKld: duty factor for deceleration timeTorqueTaTrTaTime• Example 2: getting duty factors of Kla, Klr and KldWith an example of the duty factor graph for FHA-25C-50 actuator,the way of getting the duty factors of Kla, Klr and Kld is describedas follows:The load conditions are the same as the example described inexample 1: the inertia load is accelerated by the maximumtorque,and is driven with a constant speed, and decelerated by themaximum torque. The displacement angle is 120 degrees andthe cycle time is 2.0 s.(1) Kla, and Kld: the speed is desired at 30 r/min asthe average of 0 and 60 r/min.Then, Kla = Kld = 7.0 from the graph.KLr(2) Klr (ex.: Klr =1.0) from the graph pointing the load torqueTr (ex. Tr= 0) and driving speed (ex: Nr=60r/min).(3) The driving time is calculated as the area of thetrapezoid of speed-time graph. Then thedisplacement angle is:θ = (N / 60) x {tr + (ta + td) / 2} x 360Then, tr = θ / (6 x N) – (ta +td) /2As the 120 deg. is equal to 0.33rev (=120/360), the driving angle at the speed of 60r/min (=1r/s) is:tr = (0.333-0.091)/1 = 0.242 s(4) Because the cycle time is 2.0s, the %ED is obtained as follows:%ED = (7 x 0.097+1 x 0.242 + 7 x 0.085) / 2 x 100 = 76%It is possible to drive the actuator with the load specifications continuously,because the %ED is less than 100%.If the %ED is excesses 100%, correct the situation by:• Changing the speed-time profile• Reducing load moment of inertia• Selecting an actuator with a larger frame sizeHarmonic Drive LLC 800-921-3332 26