CPC H02P 6/17 (2016.02) | 14 Claims |
1. A speed calculation device that calculates a speed of an object to be driven from output pulses obtained from an encoder connected to the object to be driven,
wherein a duty ratio of a time of a half cycle from a rising edge to a falling edge of the output pulses to a time of a full cycle between rising edges of the output pulses is measured based on a motor speed instruction,
wherein the speed calculation device outputs a duty measurement-in-progress signal while the duty ratio is being measured, and the motor speed instruction is fixed to a most recently determined value while the duty measurement-in-progress signal is being outputted,
wherein the speed is calculated using the half cycles of the output pulses if the duty ratio is within a prescribed range, and
wherein the speed is calculated using the full cycles of the output pulses if the duty ratio is outside of the prescribed range.
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