FANUC 16i/18i/21i hardware connection and troubleshooting

FANUC Series 16i/18i/21i MODEL B CNC Hardware Connection and On site Maintenance Guide

In the field of CNC machine tools, FANUC's Series 16i, 18i, 21i MODEL B (as well as enhanced models with the suffix "i") are still in service in a large number of devices due to their stable performance and powerful functionality. For on-site maintenance engineers, facing a FANUC CNC system that has been running for many years, every link from power supply connection, I/O wiring, servo and spindle connection, to emergency stop circuit design and battery replacement can become the source of faults. This article is based on the hardware connection manual of the CNC series, combined with on-site practical experience, to provide a complete technical guide from installation specifications to troubleshooting.

Installation and environment: Building a solid foundation for reliable operation

The FANUC CNC control unit is an open device and must be installed in a closed control cabinet with a protection level of not less than IP54. Strictly follow the following requirements during installation to avoid early failures caused by poor heat dissipation or interference.

1.1 Cabinet heat dissipation and spatial spacing

Control unit heat dissipation: The control unit is equipped with a built-in fan, allowing air to enter from the bottom and exit from the top. Therefore, a ventilation gap of at least 100mm must be reserved above and below the unit (this gap is still recommended for units with fans). It is strictly prohibited to install the control unit horizontally or upside down.

I/O module spacing: Connector Panel I/O modules also require a gap of 100mm above and below for wiring and ventilation. Devices with high heat generation, such as power supplies and transformers, should not be installed under the I/O module.

Cabinet surface: For small operator's panels, their heat dissipation capacity is approximately 8W/m ² ·℃ for coated metal surfaces and 3.7W/m ² ·℃ for plastic surfaces. If the total internal heat generation exceeds the cooling capacity of the cabinet, a heat exchanger or fan must be installed.

1.2 Anti noise measures: grouped wiring, shielding, and grounding

The signal lines of the CNC system are divided into three groups according to anti-interference requirements:

Group A: Main power line (AC 220V), secondary power line, servo motor power line, AC/DC relay/solenoid valve coil line. These cables must be separated from groups B and C by at least 100mm or use electromagnetic shielding.

Group B: DC 24V solenoid valve/relay wire, DI/DO wire from CNC to high-voltage cabinet. Try to stay away from Group A as much as possible and it is recommended to add shielding.

Group C: I/O Link cables, position/speed feedback cables, handwheel wires, RS-232C communication wires, battery wires, etc. between CNC and I/O units. Shielding treatment must be carried out.

Grounding points:

The protective grounding (PE) resistance should be ≤ 100 Ω (Class D grounding), and the cross-sectional area of the grounding wire should not be less than that of the power line.

The SG (signal ground) terminal of the CNC control unit must be connected to the grounding copper bar inside the cabinet with the shortest wire (recommended<30cm).

The shielded cables of servo amplifiers and spindle amplifiers must make extensive contact with the grounding plate through cable clamps, rather than being single ended grounded through thin wires. The grounding plate material should be nickel plated steel plate (thickness ≥ 2mm).

1.3 Noise Suppressor and Lightning Protection

For AC/DC relays and solenoid valves, CR spark suppressors (capacitors+resistors in series) must be installed at both ends of the coil. The resistance value is taken as the DC resistance of the coil, and the capacitance value is approximately I ²/10~I ²/20 μ F (I is the steady-state current). Varistor cannot be used alone as it cannot suppress voltage spikes.

To prevent lightning strikes, it is recommended to install surge absorbing components (such as Okaya's R · A · V-781B) between input power lines and between lines and ground. The total length of the connection between the absorbing component and the protected equipment during installation should be ≤ 2m.

Power System and Battery: Power on Timing and Data Preservation

2.1 Specification of 24V DC power supply

The CNC control unit, peripheral I/O modules, LCD units, etc. all require stable 24V DC input. The external power supply must meet the following requirements:

Output voltage:+24V ± 10% (including ripple and noise, 21.6V to 26.4V)

Instantaneous power outage holding time: ≥ 10ms (100% load drops to 0) or ≥ 20ms (50% load)

For machine tools with vertical axes, it is recommended to use a power supply with a longer holding time to reduce the distance of the vertical axis falling during power failure.

Not recommended power circuit:

The use of simple rectification filtering (only diode+capacitor) cannot maintain the output voltage during instantaneous power failure.

Connecting the CNC to a high-power load that frequently starts and stops (such as a large contactor) on the same 24V output line can cause the voltage to drop instantly below 21.6V.