Full Closed-Loop Function Description of A6 Servo Motor

1. Functional Overview

Unlike an encoder mounted on the rear end of a servo motor, which also forms a closed-loop control system—where the drive issues motion commands and the encoder feeds back the motor's real-time operating status to the drive—the system is, from the perspective of the entire machine, still only a “semi-closed-loop control.”
In simple terms, the motor-mounted encoder can only detect how many revolutions the motor has made and what position it has reached. It does not know the actual movement status of the load connected to the motor shaft. Traditional solutions estimate this information through electronic gear ratios or other calculation methods.
With the full closed-loop function, an external position detection device (such as a linear encoder or magnetic scale) can be directly installed on the load side (e.g., worktable, ball screw end, etc.). The servo drive can then directly obtain the actual position of the load, thereby eliminating mechanical transmission errors and achieving extremely high positioning accuracy.
Note: Among the A6 servo products currently available, only the RS series supports the full closed-loop function.

2. Wiring Description

We directly present the wiring details. At the drive's CN1 port, pins 21, 22, 25, 23, 13, and 24 are used for encoder signal input.

Wiring notes:

1. The drive has a built-in 5V output power supply, which can be used to power the external secondary encoder. If this internal 5V supply is used, the corresponding GND should be connected to PIN 16, paired with PIN 15.
2. A differential signal secondary encoder must be used.

Encoders such as a 5-wire single-ended type with signals like VCC, A, B, Z, and 0V are not recommended. Although in certain low-speed, interference-free laboratory environments a single-ended encoder may be connected to the servo drive through a signal conversion/amplification board, in practical industrial full closed-loop applications, almost all mainstream servo brands (such as Panasonic, Mitsubishi, Yaskawa, Siemens, etc.) do not support and do not recommend using single-ended encoders as external feedback for full closed-loop systems. Their anti-interference capability is extremely poor, and pulse loss may occur. A full closed-loop system does not allow the loss of even a single pulse.
3. The external secondary encoder must at least provide A and B quadrature differential output signals.

In full closed-loop applications, the Z signal (zero pulse/index signal) from external measuring devices (such as linear scales or magnetic scales) is generally not required and can be omitted. However, this is only acceptable when hardware-level high-precision homing using a linear scale is not required. For normal operation, positioning, backlash compensation, and vibration suppression, the system relies entirely on the A and B quadrature signals, so the Z signal is optional.
For the A6-RS series drives, when the Z signal is not used, attention must be paid to parameter C00.17:

This parameter is used to detect whether the signal wiring is functioning properly. The factory default is set to 1 (detect only A and B phase wiring integrity). When the external secondary encoder does not use the Z signal, no additional adjustment is required. If the Z signal is used, set C00.17 = 2 (detect A, B, and Z phase wiring integrity), then power off and restart the drive for the setting to take effect.

3. Required Parameter Settings

After completing the wiring as described above, the steps to enable full closed-loop control are as follows:

1. Key step: Set C00.1A = 2.

By default, the ABZ port function is used for frequency division output. It must be switched to full closed-loop function mode. Power off and restart the drive for the setting to take effect.

2. Set C1B.00 = 1 (external encoder) to enable external encoder feedback mode. Power off and restart the drive for the setting to take effect.
3. Set C1B.01:

Enter the servo drive JOG mode and perform low-speed jogging in the same direction. Observe the internal encoder pulse feedback value C1B.10 and the external encoder pulse feedback value C1B.12.

• If both values change in the same direction (both increase or both decrease), keep C1B.01 = 0 (default).
• If they change in opposite directions, set C1B.01 = 1, then power off and restart the drive for the setting to take effect.

4. Set C1B.04:

This parameter is used to determine the resolution of the external encoder (i.e., the number of external encoder pulses corresponding to one full motor revolution). Continue jogging the motor via JOG mode.
Observe the internal encoder pulse value C1B.10 to confirm when the motor completes exactly one revolution, then calculate the change in the external encoder pulse value C1B.12 (calculation method is detailed in the manual, page P). Set C1B.04 to the absolute value of this change.
A practical calculation method is as follows:
Before rotation, assume the internal encoder value C1B.10 = X1 and external encoder value C1B.12 = Y1.
After rotation, assume C1B.10 = X2 and C1B.12 = Y2.
Then:
C1B.04 = (Motor internal encoder pulses per revolution, e.g., 10000) × (Y2 − Y1) / (X2 − X1)
The result must be a positive value; otherwise, it indicates that C1B.01 may be set incorrectly.
Other C1B parameters can be fine-tuned during actual commissioning and are not covered in detail here.

4. Precautions for External Encoders, Linear Scales, etc.

1. If the encoder supply voltage is 24V, it must be powered by an external power supply. Do not connect it to PIN 15.
2. Twisted-pair shielded cables must be used (preferably each differential signal pair is individually twisted, with an additional overall outer shield layer for the entire cable).
3. Signal cables for magnetic scales and linear scales must be routed separately from the servo motor power lines (U/V/W) and braking resistor cables. Maintain a distance of at least 20 cm, and under no circumstances should they be bundled together.
4. The shielding layer must be grounded at a single point on the servo drive side (connected to the drive housing or a dedicated PE terminal, as shown in the diagram). Grounding at both ends may form ground loop currents, which can introduce interference.

Updated on: 29/06/2026