Specifications

Chapter 2 Functions
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2-2-4 Tuning Servo gains
The HA-655 driver is fed back position and speed signals in the position mode as follows:
In the figure, the closed loop of [speed control block]→[power amplifier]→[actuator]→[encoder]→[speed
control block] is called a [speed loop].
In the same manner, the closed loop of [position control block]→[speed control block]→[power amplifier]
→[actuator]→[encoder]→[position control block] is called a [position loop].
The details of the loops are explained as follows:
◆ [Position control block] and [position loop gain]
(1) The first function of the [position control block] is the [error count] calculation by the [error counter]
in the block subtracting a feedback count from a command count.
(2) The second function is the block that converts the [error count] to a [speed command] multiplying a
factor, and then transmits the [speed command] to the [speed control block]. The factor (Kp) is
called [position loop gain].
It is clear in the formula that a large [error pulse] is converted into a high [speed command] and a
zero pulse into a zero speed command, in other words, a stop command.
(3) If the [position loop gain (Kp)] is high, a small [error count] is converted into a higher [speed
command]. That is to say, higher gain provides the servo system with better response.
However, very high gain commands result in high [speed commands] from very minimal [error
count] which will result in overshooting. To compensate for the overshoot the [position control block]
generates a high speed reverse command, then overshoots in the opposite direction * * * finally
hunting motion may take place.
Conversely, if the [position loop gain (Kp)] is very low, you will get very slow positioning motion
(undershoot), and a poor servo response.
(4) In conclusion, it is important to set the optimum value to the [position loop gain (Kp)]. The HA-655
driver has been set with the most suitable value for general applications as a factory default. If the
load inertia is very heavy and the default is not suitable, tune it carefully.
● Tuning method
[Tune mode]→[2: position loop gain]
HA-655 driver
Position
command
Position
control block
Speed feedback
Actuator
Speed
control block
Position feedback
Driven
mechanism
Encoder
Power
amplifier
Speed loop
Position loop
countErrorKp ×Ｖ＝