Skip to content

Fanuc Keep Relay Parameters Exclusive -

Note: Exact exclusive Keep Relay addresses vary by FANUC controller series and PMC model (Ladder I, II, III, etc.). Always verify against the specific controller’s manual set.

In Fanuc CNC systems, Keep Relays (K-parameters) are specific memory addresses that store binary (0 or 1) settings to control machine behavior or enable/disable PLC functions. Unlike standard NC parameters, Keep Relays are often defined by the Machine Tool Builder (MTB)

, meaning their functions are exclusive to the specific machine model or manufacturer. 1. Understanding Exclusive Functions

Because Keep Relays are PLC-based (PMC), they are used to manage functions that are not built directly into the Fanuc software but are instead added by the builder. Customization:

Builders use K-relays to toggle features like tool changers, door interlocks, or coolant options. Non-Volatile:

They are "kept" in memory even when power is turned off, ensuring the machine configuration remains stable. Variable Use:

K0 through K15 are typically reserved for the machine sequence (builder-defined), while K16 and higher are often reserved for system management. 2. Common Keep Relay Examples

While functions vary, many builders follow similar patterns for common machine operations: Typical Function Description Reference Return May force a homing sequence before automatic operation. Door Interlock Enables or bypasses safety door lock signals. ATC Configuration

Selects between different tool changer types (e.g., Rack vs. Umbrella). Spindle Safety

Controls if the spindle can rotate while the door is unlocked. System Access

Often used to enable specialized menus for loading/saving ladder diagrams. 3. How to Modify Keep Relays

To change an exclusive K-relay setting, you must typically follow these steps to unlock the system: Enable PWE: , press the OFFSET/SETTING key, find the "SETTING" soft key, and change PARAMETER WRITE (PWE) from 0 to 1. Navigate to PMC: hard key, then use the right arrow soft keys to find PMC MAINTENANCE Access Keep Relays: Select the KEEP RELAY Edit Values: fanuc keep relay parameters exclusive

Use the cursor to find the target address (e.g., K5.4). Note that bits are read right to left (Bit 0 to Bit 7). Save & Reset:

Change the bit to 1 or 0, then immediately return to the Setting screen to set PWE back to 0 4. Critical Documentation

Because Keep Relay assignments are unique to each builder, you should always consult the following: Machine Builder's Ladder Diagram: Often found in the back of the electrical manual. Maintenance Manual:

Look for the "PMC Parameter List" section specific to your machine's serial number. Ladder Search:

If documentation is missing, you can search for the "K" address directly within the PLC ladder on the CNC screen to see what output it triggers. Fryer Machine Systems How to Enable Parameter Write Enable (PWE) on a Fanuc CNC

In Fanuc CNC systems, Keep Relays (K-parameters) are software-based latching relays within the Programmable Machine Control (PMC) that maintain their state (ON or OFF) even after the power is cycled. These parameters are primarily used by machine tool builders to enable or disable specific machine options, bypass sensors for maintenance, or configure custom logic without rewriting the entire ladder program. Key Characteristics of Keep Relays

Non-Volatile Memory: Values are stored in non-volatile memory, ensuring that settings like a chip conveyor's "on" status or safety bypasses persist after a restart.

Address Structure: Addresses are typically represented in an 8-bit format (e.g., K0.0 to K0.7). Some ranges are reserved for system functions (often K900+), while others are for machine-specific OEM functions.

Maintenance & Debugging: They are vital for bypassing faulty sensors (like a conveyor rotation sensor) to keep production running while awaiting repairs. Accessing and Modifying Keep Relays

To modify these parameters, you generally need to put the machine in MDI mode and enable "Parameter Write".

Enable Parameter Write: Navigate to the Setting Screen and set PARAMETER WRITE to 1. Navigate to PMC Maintenance: Press the SYSTEM key. Select the PMC soft key. Choose PMCPRM (PMC Parameters) and then KEEP-RL. Note: Exact exclusive Keep Relay addresses vary by

Safety Precautions: For certain system keep relays (like K900), values may only be visible or changeable when the Emergency Stop is pressed. Common Applications

Machine Options: Enabling/disabling features like chip conveyors, coolant types, or tool management systems.

Logic Interlocks: Modifying turret rotation requirements (e.g., allowing rotation without requiring the X/Y axes to be at home) to reduce cycle time.

System Controls: Bypassing safety circuit interfaces or hiding specific system screens. Important Documentation

Because keep relay assignments are determined by the Machine Tool Builder (MTB), their functions vary between machines. It is critical to consult the machine’s Ladder Diagram or Maintenance Manual provided by the manufacturer to identify what each specific K-address controls. Fanuc Keep Relay Parameters Overview | PDF - Scribd

Title: The Guardians of Automation: The Criticality and Application of FANUC Keep Relay Parameters

In the intricate ecosystem of FANUC CNC systems, the distinction between volatile memory and non-volatile memory is the line between a machine that remembers its purpose and one that resets to oblivion upon reboot. At the heart of this distinction lies the "Keep Relay" (often designated by addresses beginning with the letter 'K'). While standard Relays (R, D, or E addresses) are essential for the logical flow of a program, Keep Relay parameters occupy an exclusive and critical tier within the ladder logic architecture. They serve as the system’s long-term memory, preserving vital operational states and configuration settings even when power is removed. Understanding the exclusive nature of Keep Relay parameters is essential for any engineer or technician aiming to maintain system integrity and prevent catastrophic data loss.

The primary defining characteristic of a Keep Relay is its non-volatility. In standard relay logic, when the power supply to the CNC unit is turned off, all relay coils are de-energized, and their contacts revert to their default states. This is acceptable for transient signals—such as a command to open a chuck or start a spindle—but it is unacceptable for data that defines the machine’s personality. Keep Relays solve this by storing their status (ON or OFF) in non-volatile memory backed by a battery or solid-state memory retention. This exclusivity means that if a Keep Relay is set to '1' (ON), it will remain '1' even after the machine is shut down, shipped across the country, and restarted. This unique property makes them indispensable for storing "latched" states, such as whether a maintenance interval has been reached, whether a specific optional function is enabled, or the last position of a tool changer.

Furthermore, the exclusivity of Keep Relay parameters extends to their role in system configuration and customization. Unlike standard internal relays, which are purely for the programmer’s logical processing, Keep Relays often bridge the gap between the PMC (Programmable Machine Controller) and the CNC system parameters. In many FANUC architectures, specific Keep Relays are hard-coded or reserved for system-level functions. For example, a specific bit in a Keep Relay might be used to enable a custom macro interface or activate a specific safety interlock that must remain active regardless of power cycles. In custom machine building, these relays are frequently used to create "personality bits"—settings that allow a single generic ladder program to adapt to different machine variants (e.g., a lathe versus a mill) by simply flipping a Keep Relay switch.

However, the power of Keep Relays comes with a significant engineering responsibility: the risk of "latched" logic errors. Because these relays retain their state, they do not naturally reset to a "safe" default state upon power-up like standard relays do. If a Keep Relay is used to latch an error state or an unsafe condition, simply cycling power will not clear the fault; the machine will wake up in an error state. Therefore, the logic surrounding Keep Relays must be exclusive and rigorous. It usually requires an explicit "unlatch" or reset condition in the ladder logic. If a technician mistakenly uses a Keep Relay for a transient signal (like a pulse to trigger a single cycle), the machine may get stuck in that cycle indefinitely. This highlights the necessity for programmers to treat Keep Relays not as general-purpose variables, but as permanent registers reserved for specific, persistent data.

The maintenance of Keep Relay parameters also requires a specialized approach compared to standard logic. In the event of a battery failure or a full memory clear, the states of these relays are lost, potentially rendering the machine inoperable until the correct "bit patterns" are restored. This underscores the importance of documentation and backup. A skilled technician knows that a backup of the PMC SRAM (Static Random Access Memory) is useless without a record of the Keep Relay states. Consequently, many facilities maintain a "Parameter Sheet" exclusively listing the active Keep Relays and their intended functions, treating them with the same reverence as the servo tuning parameters. In the world of FANUC CNC controls (Series 0i, 31i, 35i, etc

In conclusion, Keep Relay parameters

In the world of FANUC CNC controls (Series 0i, 31i, 35i, etc.), Keep Relays (often referred to as K parameters or K addresses) are the unsung heroes of machine configuration. Unlike common system parameters that adjust servo loops or axis scaling, Keep Relays are discrete, bit-level switches that dictate machine-specific logic behavior.

However, a common pitfall in shops and integration shops is the mismanagement of these bits. This article focuses on a single, golden rule: Treat every Keep Relay as an exclusive parameter.

Fanuc provides the hardware and core firmware, but the Machine Tool Builder (e.g., Haas, Mazak, DMG MORI, Doosan) defines the Keep Relay map. This means:

Most modern Fanuc controls (Series 31i, 32i, 0i-D and later) allow OEMs to apply read/write protection to specific ranges of Keep Relays.

Imagine a CNC machining center where:

Result: High-pressure coolant stops working randomly, but no alarm triggers. Debugging this takes hours because the ladder shows the same bit in two unrelated rungs.

This is the classic symptom of a non-exclusive Keep Relay conflict.

| Keep Relay | Exclusive Function | Controller | |------------|--------------------|-------------| | K17.0 | Enable/Disable soft overtravel check | CNC Series 0i/30i | | K17.1 | Enable absolute position detection | CNC Series 0i | | K9.3 | Power-on automatic reference position return | CNC Series 16i/18i | | K19.0 | Skip signal polarity selection | CNC Series 31i | | K40.0 | Enable/Disable PMC ladder editing | All CNC models | | K43.0 | Tool life management bypass | CNC Series 15i | | K50.0 | Spindle orientation direction | CNC Series 21i |

  • Use spare ranges: Most builders reserve blocks (e.g., K90–K99) for field customization. Stay within those blocks to avoid conflict.
  • Lock critical bits: Use the FANUC password function or parameter write protection (PWE) to prevent accidental changes.

    • While Keep Relays hold data without power, they are often excluded from standard SRAM backups unless specifically configured. When cloning a machine, failure to clear or set the correct Keep Relays can lead to configuration mismatches.