position / speed mode - Harmonic Drive LLC

Chapter 2Functions
[Speed control block], [speed loop gain], and [speed loop integral compensation]
(1) The first function of the [speed control block] is to subtract a feedback signal from a command
signal.
(2) The second function is the block converts the difference to a [current command] multiplies it by a
factor, and then transmits the [current command (I)] to the [power amplifier]. The factor (Kv) is
called [speed loop gain].
It is clear in the formula that a significant [speed difference] is converted into a high [current
command] and zero difference into zero current command, in other words, a stop command.
(3) Just as with the [position loop gain], higher gain provides better response and excessive gain
results in hunting. Low gain requires no hunting but raises the occurrence of undershoots.
(4) The [speed loop integral compensation (Tv)] of The HA -655 driver makes less influence on load
fluctuation.
⎛ 1 ⎞
IKv
× ⎜1 +
⎟ × speed difference
⎝ Tv S ⎠
If the [speed loop integral compensation (Tv)] is smaller, the speed response to the load fluctuation
becomes better, but too small a value results in hunting. Excessive compensation requires no
hunting, but will result in a poor response for load fluctuation.
Tuning method
[Tune mode][0.speed loop gain], and [1: speed loop integral compensation]
Feed forward gain
I Kv ×speeddifference
(1) In the position mode The HA-655 driver controls the error count, (the difference between
[command pulse] and [feedback pulse]), to be [0]. At the beginning of inputting a command pulse
train, the actuator starts slowly because of small error count.
(2) The [feed forward] function may accelerate the actuator as much as possible, adding speed pulses
converted from the command pulse frequency directly to the driver’s speed control loop.
HA-655 driver
Speed command = Kp x Error pulse +speed pulse x Feed forward gain
Differential
Feed forward
Load
mechanism
Position
command
Position
control block
Speed
control block
Power
amplifier
Actuator
Speed feedback
Position feedback
Encoder
(3) The relation between the feed forward and actuator motion is as follows:
Higher feeding allows for better following to command, but excessive feeding results in hunting and
erratic motion.
Low feeding requires no hunting but a poor following of the command.
Tuning method
[Tune mode][3:Feed forward]
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