FANUC Axis card A20B-3300-0033 A20B33000033 A2OB-33OO-OO33

A20B-3300-0033 | FANUC 2-Channel FSSB Servo Controller Card — 16i / 18i / 21i / FSSB Fibre Optic Interface / Plug-In Module

FSSB — Why Fibre Optic Servo Communication Matters

Servo communication in modern FANUC CNC systems travels over optical fibre. The reason is electrical noise. A servo drive cabinet contains:

• High-current, high-frequency motor current switching
• Large capacitor banks charged to 300–600VDC
• Fast-switching IGBT transistors generating electromagnetic emissions across a broad frequency spectrum

In this environment, a copper cable carrying position command signals is vulnerable. Any noise coupling onto the servo command wire adds noise to the position command — producing following error, velocity ripple, and reduced surface finish on the machined workpiece.

Fibre optic transmission is completely immune to electromagnetic interference. The FSSB fibre optic link carries the same position commands and encoder feedback data as a copper cable alternative, but the light signal cannot be coupled to or from by electromagnetic fields. The A20B-3300-0033 generates the FSSB optical transmission signals and processes the returning optical feedback signals — bringing this noise immunity directly into the servo communication for the two controlled axes.

Key Specifications

2-Channel Capacity — Matching the Machine

The A20B-3300-0033 provides exactly 2 FSSB channels from a single plug-in card. Its capacity directly matches the most common configurations:

2-axis turning centre (X and Z): One A20B-3300-0033 controls both axes. A simple CNC lathe's complete servo interface fits on this single card.

2-axis of a larger system: For a 4-axis machining centre, one A20B-3300-0033 handles the first two axes (typically X and Y) while a second card handles Z and the fourth axis. Each card operates independently on its own FSSB channel.

First 2 axes of a 5-axis CNC: The first A20B-3300-0033 covers axes 1 and 2; additional cards extend to the other axes as needed.

The plug-in architecture makes axis count expansion straightforward — add a card, and the CNC gains two more FSSB servo channels on the same main board.

Application Scenarios

FSSB communication alarm on both controlled axes: A FANUC 18i turning centre generates FSSB communication alarms on both X and Z axes simultaneously. Both servo drives and motors test correctly independently. The A20B-3300-0033 servo card is identified as the fault. Replacement restores FSSB communication on both axes.

System expansion: A 2-axis 21i CNC is reconfigured for 4-axis operation. A second A20B-3300-0033 is installed on the main board alongside the existing card, providing the two additional FSSB channels needed for the new axis configuration.

FAQ

Q1: Can the A20B-3300-0033 connect to servo drives other than Alpha-i FSSB-type amplifiers?

The A20B-3300-0033 uses FANUC's FSSB fibre optic protocol, which is compatible with FANUC Alpha-i and Beta-i servo amplifiers equipped with FSSB input ports. Older Alpha series amplifiers using Type-A or Type-B serial interfaces are not FSSB-compatible and cannot connect to the A20B-3300-0033. Confirm the servo drives' interface type before fitting this card.

Q2: How is the FSSB node address assigned to each servo amplifier on the daisy-chain?

FSSB address assignment is defined by the physical order of amplifiers on the fibre optic chain combined with CNC parameter settings. The first amplifier in the chain typically takes the lowest address; subsequent amplifiers take higher addresses in sequence. The FSSB configuration parameters in the CNC (FSSB setting screen) define the number of amplifiers and their axis assignments. After fitting a replacement A20B-3300-0033, the existing FSSB parameters remain in the CNC's SRAM and should re-establish communication automatically on power-up.

Q3: Can a system with two A20B-3300-0033 cards (4-axis) operate if one card fails?

When one A20B-3300-0033 fails, only the two axes on that card's FSSB channel generate alarms. The other card and its two axes continue to operate normally. Depending on the CNC configuration, the machine may be able to execute limited operations using the remaining working axes while the failed card is being replaced. This partial operation depends on whether the PMC ladder allows machine cycle execution with some axes inhibited.

Q4: Does the optical fibre cable require special handling or maintenance?

FSSB fibre cables should be protected from sharp bends, tight radius routing, and mechanical damage. The minimum bend radius for the applicable cable type is specified in the FANUC connection manual. Connector end faces should be kept clean — contamination on optical connector faces attenuates the light signal, potentially causing intermittent FSSB communication errors. When inspecting an FSSB communication fault, check the fibre cable and connector condition alongside the A20B-3300-0033 card.

Q5: Is the A20B-3300-0033 specific to the i-generation CNCs, or can it be used with 0i-D or 30i systems?

The A20B-3300-0033 is confirmed for FANUC Series 16i, 18i, and 21i (Model A and B). Different CNC generations use different servo card variants — the 0i-D and 30i platforms use different main board hardware and require their own specific servo cards. The A20B-3300-0033 is the correct card for the 16i/18i/21i generation and is not interchangeable with 0i-D or 30i servo cards.