Specifications

Chapter 2 Functions
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2-3-3 Tuning servo gains
The HA-655 driver is fed back position and speed signals in the speed mode as follows:
In the figure, the closed loop of [speed control block]→[power amplifier]→[actuator]→[encoder]→[speed
control block] is called [speed loop].
The details of the loop are described as follows:
◆ [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 when the block converts the difference to a [current command] multiplies it
by a factor, and then transmits the [current command] to the [power amplifier]. The factor (Kv) is
called [speed loop gain].
It is clear in the formula that a [speed difference] is converted into a high [current command], and a
zero difference into a zero current command, in other words, a stop command.
(3) If the [speed loop gain (Kv)] is high, a small [speed command] is converted into a higher [current
command]. That is to say, higher gain provides the servo system with a better response.
However, very high gain settings can cause a very high [current command] in response to a small
[speed command] which will result in overshooting. To compensate overshooting, the [speed
control block] generates a high speed reverse command, then ・・・・・・・・・ finally hunting motion
may take place.
(4) Conversely, if the [speed loop gain (Kv)] is very low, you will get very slow positioning motion
(undershoot) and poor servo response.
(5) The [speed loop integral compensation (Tv)] of the HA-655 driver minimizes the influence of load
fluctuation.
If the [speed loop integral compensation (Tv)] is low, the speed response to the load fluctuation
becomes better, but very small value can result in hunting. Excessive compensation requires no
hunting but a poor response for load fluctuation.
● Setting
[Tune mode]→[0: speed loop gain], [1: speed loop integral compensation]
HA-655 driver
Speed
control block
Speed
command
Position
control block
Speed feedback
Actuator
Position feedback
Driven
mechanism
Encoder
Power
amplifier
Speed loop
difference
speed×KvI＝
difference
speed
1
1 ×








+×
STv
KvI＝