HarmonicHarmonic Drive™ servo

always possible due to the influence of external forces, acceleration, and deceleration. Establishing a 

positioning allowance is a good solution to the problem; that is [in-position range]. 

[Tune mode]→[4: in-position range] sets the allowance. The actuator position comes within the range 

calculated with the formula below, the [CN2-33: in-position] signal outputted.

2-3 Speed mode

The HA-655 driver makes use of either the position control or the speed control. This section describes 

the speed mode. (※ The default setting is the [position mode].

Before running, set the control mode by [parameter mode] → [0: control mode].

2-3-1 Speed conversion factor

In the speed mode, the command is sent from a host with an analog voltage signal. The [speed 

conversion factor] converts the [speed command] voltage to motor speed.

The [speed conversion factor] is the motor speed when the [speed command voltage] is [10V]. The 

actual motor speed is obtained by the following formula:

The [speed monitor] (SPD-MON: CN2-23pin) output voltage as follows:

● Setting

[Parameter mode]→[9: speed conversion factor]

2-3-2 Voltage of speed command

Input the voltage converted by the [speed conversion factor] into [CN2-31: speed command] and 

[CN2-32: speed command common] pins. The [speed command voltage] is obtained by [parameter 

mode]→[9: speed conversion factor].

◆ FWD enable and REV enable

The HA-655 driver provides [FWD enable] and [REV enable] input ports. The rotary direction of the 

actuator is decided by the polarity of [CN2-31: speed command SPD-CMD] and ON/OFF states of [FWD 

enable] and [REV enable] as shown in the table below:

CN2-31 Speed cmd.: SPD-CMD ＋Command －Command

CN2-4 FWD enable: FWD-EN ON OFF ON OFF

CN2-5 REV enable: ON Zero clamp, zero speed REV rotation Zero clamp, zero speed FWD rotation

REV-EN OFF FWD rotation Zero clamp, zero speed REV rotation Zero clamp, zero speed

● Relating input pins

CN2-31: speed command, CN2-32: speed command common, CN2-4: FWD enable,CN2-5:REV enable

◆ Speed command offset

In the speed mode, the motor may rotate slightly in spite of a [0V] speed command voltage. This problem 

may occur when the speed command voltage has an offset of a few milli-volts. This function removes the 

slight rotation compensating the command voltage offset.

While inputting a [OV] command voltage adjust the speed command offset until the actuator stops 

rotating.

[Speed command automatic offset] function is also provided.

● Setting

[Tune mode]→[9: speed command offset], [test mode]→[So: Speed command automatic offset]

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]

2-3-4 Command change

The function can operate the actuator without command at the speed specified by [tune mode]→[6: 

internal speed command]. This is convenient for diagnosis and for test operation without hosts.

The actuator will rotate at the speed set by the [internal speed command] when a signal is input to

CMD-CHG (CN2-6) and stops when the signal is removed.

● Relating I/O pin

Input pin: CN2-6

2-3-5 Acceleration / deceleration time constants

[Acceleration time constant] is the time it takes to accelerate the motor from [0 r/min] to the speed of [A: 

speed limit] of [parameter mode].

[Deceleration time constant] is the time it takes to decelerate the motor from the speed of [A: speed limit]