User Manual for Absolute Positioning Function of A6 Series Servo Motors

The absolute positioning function of servo motors refers to the motor’s ability to accurately recognize its current position (absolute position) immediately after power loss or restart, without needing to return to a reference origin. The core hardware foundation of this function is the absolute encoder. All A6 series servo motors are equipped with a 17-bit absolute encoder. To use the absolute positioning function, a dedicated cable with a battery box is required, as shown in the figure below:

The function of the battery is simple: to supply power to the motor’s encoder. The encoder requires a power supply to maintain position data. When the driver is restarted or powered off, it cannot supply power to the encoder. Therefore, adding a battery to the encoder cable is the optimal solution to ensure that position data is not lost. It can be understood as an independent backup power source.

(Note: If the absolute positioning function is enabled with a standard cable without a battery box, the driver will trigger an alarm.)

1. Instructions for Enabling the Function

1. Connect the servo motor and driver using the encoder cable with a battery box.
2. Configure the driver parameters. The A6 series provides five absolute positioning modes, which can be selected based on actual application requirements:

• Absolute Linear Mode: Maps the multi-turn absolute position of the encoder linearly to a preset linear stroke. Suitable for linear reciprocating motions such as linear modules, slides, and gantry systems. The encoder’s multi-turn absolute data changes within a fixed range without the risk of position overflow.
• Absolute Linear Endless Mode: Suitable for scenarios where the motor rotates continuously in one direction. Position data accumulates indefinitely, and the driver will not trigger position overflow alarms.
• Absolute Encoder Single-Turn Mode: The simplest absolute mode. This mode does not record multi-turn data but only single-turn position information. Suitable for applications where the motion range does not exceed one rotation, such as robotic arm joints, rotary valves, angular positioning stages, and indexing tables.
• Absolute Rotary Mode: The standard and most commonly used multi-turn absolute mode. Each encoder value uniquely corresponds to an absolute mechanical position of the motor shaft. Suitable for most rotary applications requiring full absolute positioning, such as robot joints, CNC tool changers, rotary worktables, and winches.
• Absolute Mechanical Single-Turn Mode: Designed for applications requiring extremely high positioning accuracy within a single rotation, where position loss after power loss is not allowed. Examples include high-precision indexing tables, precision valves, and radar pitch mechanisms. Similar to the absolute encoder single-turn mode, it is more reliable as the driver actively ignores turn counts. Even if the motor accidentally rotates beyond one turn, the feedback position is "folded" within one rotation, preventing erroneous values like 361°, thereby ensuring greater system stability.

For demonstration purposes, the following steps are explained using software (the process is the same whether using the driver panel or other methods):

1. Open the C00 group configuration parameters.
2. Locate C00.07 and select the desired absolute positioning mode.
3. Save the settings.

Afterward, power off and restart the driver for the absolute positioning function to take effect.

2. Explanation of Absolute Positioning Parameters

First, review the parameters in the driver’s U40 group related to the encoder:

• U40.16 (Absolute Position Feedback (Command Units)):

Displays the total motor position in command units, related to C00.02. For example, if C00.02 = 10,000, the motor completes one rotation per 10,000 command units. Parameter value = motor rotation turns × 10,000.

• U40.18 (Absolute Position Feedback (Encoder Units)):

Displays the total motor position in encoder units, related to encoder resolution. For example, with a 17-bit encoder, the motor completes one rotation per 131,072 encoder units. Parameter value = motor rotation turns × 131,072.

• U40.1C (Encoder Single-Turn Information):

Determined by encoder hardware. As above, one motor rotation corresponds to 131,072 encoder units, as shown in the figure below:

Regardless of how many turns the motor rotates, the single-turn position information remains fixed, consistently following the pattern 0 → 65536 → 131072 → 65536 → 0. This represents the encoder’s single-turn absolute position information. As soon as the motor stops, its specific position within one rotation can be obtained.

• U40.1E (Encoder Multi-Turn Position Information):

This is the most critical information for multi-turn absolute positioning. When the motor enables absolute positioning modes other than single-turn mode, the cumulative turn count is reflected here each time the motor completes a rotation.

• U40.24 (Absolute Position Feedback (Encoder Units) Lower 32 Bits):

This parameter accumulates the encoder’s absolute position but has an upper limit ranging from -2,147,483,648 to 2,147,483,647. Once this limit is exceeded, the count cycles continuously. However, each time the cumulative count exceeds 2,147,483,647 (2^31) encoder units, the upper 32-bit parameter U40.26 increments by 1.

• U40.26 (Absolute Position Feedback (Encoder Units) Upper 32 Bits):

As described above, the upper 32 bits prevent count overflow. Combined, the multi-turn data capacity is 64 bits.

A simple position calculation example is as follows:

Current Absolute Position = U40.26 / 2 × 65536 × 131072 (encoder bits) + U40.1C = U40.1A + 2^32 × U40.26.

3. Common Issues and Solutions

1. What is the battery lifespan? How can I purchase replacement batteries?

The battery is theoretically usable for two years, but actual lifespan may vary significantly depending on operating conditions and environment. Regular replacement is recommended. The battery model used is ER14505. Replacement batteries can be purchased on platforms such as Amazon or eBay. The A6 driver provides the ALF9.0 alarm, which notifies the user when the battery voltage is too low.

2. Why does the driver still trigger an alarm after setting C00.07 and power-cycling?

If the absolute positioning function is being enabled on the servo motor for the first time, it is actually necessary to perform two power‑off and restart cycles:

• Set parameter C00.07 and save it successfully.
• Power off and restart the drive.

At this point, the drive will trigger an ER20.8 alarm. At this stage, you need to write the command to reset the encoder data into parameter F31.10, as shown below:

After that, power off and restart the drive again. You can then check whether the absolute function has been successfully enabled via the status interface:

As shown in the figure, the drive is online and operating normally, indicating that the absolute positioning function has been successfully enabled. This two‑step restart process is only required for the initial activation of the absolute function. For subsequent changes to C00.07 or when switching between absolute positioning modes, only one restart is needed.

3. Why is the position data lost after power-cycling, even with the battery box cable?

First, check the battery. It may be depleted or faulty. Test with a spare cable without moving the motor to verify.

Second, review other parameters in the driver’s U40 group to determine whether all data is lost or only specific parameters. If this occurs, contact our support team for assistance.

Finally, if the PLC loses data but the driver retains it, the issue may lie in the PLC connection. Inspect the connection interface for potential issues.

4. How to clear absolute position data?

If you need to clear all position data, please refer to the following steps:

• Locate the homing function.
• Here, directly select “Use Only Motor Z Signal.”

As shown in the figure below, the mode will automatically change to 34. Other settings do not need to be modified and can remain at their default values. (Mode 34 is relatively convenient and the simplest option.)

Click the Start button to enable homing.

The motor will rotate slowly until it returns to the zero position, as shown in the figure below.

If you only need to clear the multi‑turn position data while keeping other positions unchanged, refer to the method described in section 2) above (F31.10 = 4). This will reset U40.1E to zero.

Updated on: 30/01/2026