FANUC CNC Controllers: Settings Method for Switching Between Full Closed Loop and Semi Closed Loop

Due to its high precision and reliability, the FANUC CNC controllers are widely used in modern machine tools. In its system settings, the choice between full closed-loop and semi closed-loop control modes is crucial for enhancing the control accuracy and stability of machine tools. Here are the two main methods for switching between full closed-loop and semi closed-loop in the FANUC CNC controllers: manual setting and one-key setup.

FANUC CNC Controllers: Manual Setting of Three Key Parameters

Parameter Settings for Switching Between Full Closed-Loop and Semi Closed-Loop

In the FANUC CNC controllers, the use of a linear scale and the type of closed-loop (full closed-loop or semi closed-loop) directly affect the control accuracy and motion response of the machine tool. In full closed-loop control mode, the position feedback signal comes from the linear scale, while in semi closed-loop mode, it relies on the motor encoder to feedback position. To ensure a correct switch, relevant parameters must be manually adjusted during operation.

Linear Scale Selection

Bit 1 (OPT) of parameter No.1815 controls whether to enable the linear scale:

When OPT = 1, the system uses the linear scale.

When OPT = 0, the system does not use the linear scale.

FSSB Setting

The FANUC CNC controllers use FSSB (FANUC Servo Serial Bus) to transmit servo control signals. During the switch, the FSSB settings need to be modified:

The setting value of parameter No.24003 needs to be changed to 1000, which is related to the specific servo drive and system configuration.

The setting value of parameter No.24096 needs to be changed from 1 to 0 to adapt to the new closed-loop settings.

Servo Initialization

To ensure the control accuracy of the servo system, relevant mechanical parameters, such as the screw pitch (usually found in the machine tool's mechanical manual), need to be set:

Parameter No.2084 and No.2085 are directly related to the screw pitch; for this machine tool, the screw pitch is 4, so No.2084 = 1, No.2085 = 250.

Parameter No.2023 and No.2024 control the number of position pulses, typically set to 8192 and 12500.

Parameter No.1821 is the reference counter capacity, set to 4000.

The gain ratio coefficient of parameter No.2185 is usually larger in full closed-loop mode and needs to be set to 0 when switched to semi closed-loop mode.

After modifying these parameters, make sure to power off and restart the system to ensure the changes take effect.

Verification After Operation

After changing the above parameters, the operator needs to enter manual pulse mode (or Jog mode) and set the magnification to the lowest to verify whether the actual displacement of the machine tool matches the coordinate display. Use a form for testing to ensure that the accuracy after the system switch meets the requirements.

FANUC CNC Controllers: One-Key Setup for Full Closed-Loop and Semi Closed-Loop Switching

To simplify operations, the FANUC CNC controllers also offer a one-key switch function, making the conversion from full closed-loop to semi closed-loop more convenient. Here are the steps for one-key setup through the operation panel:

Set FSSB Parameters Through the System Panel

Press the "system" button on the operation panel to enter the setting interface and find the FSSB setting.

In the axis interface, change the setting value from 1 to 0. This step will switch from full closed-loop mode to semi closed-loop mode.

Modify Servo Settings Parameters

Enter the servo setting screen and change the external encoder connection setting value from 1 to 0. After the modification, remember to press the “set” button to save the changes.

In parameter No.1815, change the value of bit 1 from 1 to 0 to disable the use of the linear scale.

Power Off and Restart for Verification

After completing the above steps, be sure to power off and restart the system. During testing, enter manual pulse mode or Jog mode, set the magnification to the lowest, and use measuring instruments to verify the consistency between the machine tool's displacement and the coordinate display.

The FANUC CNC controllers provide flexible and efficient full closed-loop and semi closed-loop switching functions. Through manual setting and one-key setup, users can finely adjust the machine tool according to actual needs, thereby optimizing production efficiency and processing accuracy. Whether manually adjusting parameters one by one or using the convenient one-key switch, the FANUC CNC controllers meet different processing requirements, ensuring the stability and efficiency of the equipment.