Fanuc Keep Relays, also known as K parameters, are a subset of PMC parameters used to control machine-specific functions and maintenance operations. Unlike standard parameters that might reset, Keep Relays are stored in non-volatile memory, meaning they retain their ON/OFF state even after the machine is powered down. Core Functionality
Keep Relays act as soft switches within the machine's ladder logic. Because their assignments are determined by the Machine Tool Builder (MTB) rather than Fanuc, their functions vary significantly between different machine brands and models. Common uses for Keep Relays include:
Enabling/Disabling Hardware: Turning optional equipment like chip conveyors or parts catchers on and off.
Safety & Interlock Bypassing: Temporarily shielding external alarms or bypassing sensors (like a faulty conveyor rotation sensor) during troubleshooting.
Operational Modes: Switching between proximity sensor-based clamping or timer-based clamping for chucks.
Cycle Optimization: Modifying tool change requirements, such as allowing a turret to rotate before axes have reached their home position to save time. Parameter Structure & Addresses
Keep Relays are typically organized into an 8-bit octal system (bits 0 through 7).
User Keep Relays (K0–K100+): Assigned by the MTB for custom machine functions like tool management, coolant control, or interlocks.
System Keep Relays (K900–K999): Reserved for core system functions, such as the safety circuit interface (e.g., K928.7 or K929.0). How to Access and Modify
Modifying these parameters requires specific steps to prevent accidental machine damage:
Enable Parameter Write: In MDI Mode, go to the Setting screen and change "Parameter Write" (PWE) from 0 to 1.
Navigate to PMC Maintenance: Press the System key, then use the soft keys to find PMC Maintenance > Keep Relay.
Find the Address: Use the cursor to select the specific K-address. Addresses are read from right to left (Bit 0 is the far right, Bit 7 is the far left). Enter Value: Type 1 for ON or 0 for OFF and press Input.
Restore Safety: Change the "Parameter Write" setting back to 0 once finished.
Note: For System Keep Relays (K900+), the values may not be visible or changeable unless the machine is in an Emergency Stop state. Get to know how to change the Keep Relay!
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 conclusion, Keep Relay parameters
In FANUC PMC (Programmable Machine Controller) logic, standard relays (Internal Relays, or R-addresses) are volatile; they reset to zero when the control power is cycled.
Keep Relays (K-Parameters) differ because they are non-volatile. They retain their status (0 or 1) even after power loss.
The term "Exclusive" in this context refers to two specific scenarios: fanuc keep relay parameters exclusive
In FANUC CNC and robot controllers, Keep Relays (K parameters) are bit-type non-volatile memory elements used to store machine-specific configuration settings. Some Keep Relays have exclusive, pre-defined functions — meaning their behavior is fixed by FANUC and cannot be reassigned by the OEM or end user.
Before discussing exclusivity, let’s define the object:
The second dimension of exclusivity is access. While most CNC parameters can be viewed via the normal "System" or "Parameter" soft keys, Keep Relays are hidden behind a deliberate procedural wall. To view or edit them on a standard Fanuc control (e.g., 0i, 31i), one typically must:
This is not a flaw; it is an exclusive design feature. Fanuc and machine tool builders intentionally sequester Keep Relays because changing them can alter safety logic, bypass limit switches, or fundamentally change the operational sequence of the machine. By making them exclusive to trained service technicians or advanced integrators, Fanuc prevents accidental toggling that could lead to crashes, injury, or non-compliant machine behavior.
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.
Some Keep Relays are exclusively "write-once" or "latching." For example, a Keep Relay that enables a paid option (like high-speed machining) may be set to 1 by an OEM field engineer and then permanently locked. Even if you try to change it back to 0, the ladder logic will ignore the change due to a memory-protect key or a secondary hardware dongle.
Rating: 9/10 for Necessity, 6/10 for User Safety.
The FANUC Keep Relay "Exclusive" concept is a fundamental requirement for modular machine building. It allows a single standard CNC control to adapt to thousands of different machine configurations.
However, FANUC’s interface for these parameters is raw. It lacks a user-friendly GUI or distinct "Read-Only" flags for critical addresses. It puts the burden of integrity squarely on the programmer and the maintenance team.
Recommendation: If you are a machine builder, use exclusive Keep Relays to define hardware existence. If you are a maintenance tech, back up your Keep Relay states before touching them, and treat them like physical DIP switches—do not flip them unless you know exactly what they do.
Keep Relays (K-parameters) are software switches in the Programmable Machine Control (PMC) that maintain their state (ON/OFF) even after a power cycle. Unlike standard parameters, Keep Relays are "exclusive" because their functions are defined by the Machine Tool Builder (MTB) , not Fanuc itself. Custom Functions:
They typically control machine-specific options like auto-door behavior, chip conveyor timers, or enabling a 4th axis. Documentation: Because they are builder-defined, the meanings of cap K 99.9
vary wildly between a Haas, a Doosan, or a Matsuura. You must refer to the Ladder Diagram
or the machine's electrical manual to find their specific definitions. The Ghost in the Ladder: A Short Story The shop floor was quiet, except for the rhythmic
of the cooling fans on the old Fanuc 0i-MC. Elias stared at the screen. The machine was "dead"—no alarms, no errors, just a stubborn refusal to start the spindle.
He’d checked the proximity sensors and the air pressure. Everything was green. On a whim, he pulled the dusty, yellowed manual from the back cabinet—the one the previous maintenance lead said "contained the machine’s soul."
He flipped to the PMC section and found a handwritten note scrawled in the margin: “Keep Relay K12.3 – The Apprentice’s Lock.” Elias navigated to the PMC parameters. There it was: cap K 0012 was set to
In the world of Fanuc, Keep Relays are the machine’s permanent memory. Unlike the volatile bits that reset when the breaker flips, these are the "Exclusive" secrets of the builder. K12.3 wasn’t a Fanuc standard; it was a custom safety latch the builder had programmed into the ladder logic years ago. He changed the bit to The contactor in the cabinet clicked—a sharp, mechanical
that sounded like a heavy bolt sliding home. The "Cycle Start" lamp flickered to life. Elias didn't know who "The Apprentice" was or why they needed a lock, but he’d just found the one bit of data that refused to be forgotten.
He closed the cabinet, the spindle beginning its low, rising howl. Some parameters are just numbers; Keep Relays are history.
Fanuc o m series 4 th axis enable parameters pls... - Facebook
Keep Relays (K Parameters) are non-volatile internal relays within the Programmable Machine Control (PMC) that retain their state (0 or 1) even after the machine is powered down. They are primarily used by Machine Tool Builders (MTBs) to toggle specific options, manage maintenance modes, or bypass safety interlocks without rewriting the PLC ladder logic. Accessing and Modifying Keep Relays
To change a keep relay, you must first enable "Parameter Write" to avoid "Write Protect" alarms. Enable Writing [OFFSET/SETTING] function key. Select the soft key and change PARAMETER WRITE Navigate to Keep Relays function key. [PMC MAINTENANCE] Select the [KEEP RELAY] soft key to view the list. Edit the Bit
Identify your target address (e.g., K0005). Bits are counted right to left , from 0 to 7. Type the new value ( ) and press : Return to the setting screen and set PARAMETER WRITE Common Keep Relay Applications Fanuc Keep Relays, also known as K parameters
While specific addresses vary by machine builder, standard "System K Parameters" and common user-defined ones include: Address Range Primary Function K00 – K15 General Sequence Bypassing door interlocks, enabling/disabling 4th axis. Memory Control Managing keep-type memory states. K17 – K19 PMC Management
Reserved for PMC software data; usually strictly for internal system use. Special Functions
Often used for system-level options like bypassing sensor inputs (e.g., chip conveyor detection). Builder-Specific Examples
Fanuc Keep Relays (K-parameters) are non-volatile PMC (Programmable Machine Control) parameters used to toggle machine-specific functions. Unlike standard NC parameters that control motion, keep relays act as software "switches" that remain in their state (0 or 1) even after power is turned off. Core Functionality
Keep relays are used by machine tool builders (MTBs) to define machine behavior without rewriting the PLC ladder. They are typically used for:
Feature Selection: Enabling or disabling options like a chip conveyor, high-pressure coolant, or an optional tool magazine.
Interlock Control: Bypassing or enforcing safety interlocks, such as door locks or spindle start conditions.
Operational Modes: Switching between different tool change (ATC) patterns or pallet change (APC) sequences. Common Keep Relay Addresses
While addresses vary by machine builder, standard Fanuc-defined ranges often include: K0 – K15: General bit parameters for machine sequences. K16: Often used for keep-type memory control.
K17 – K19: Reserved for PMC managing software data; these should generally not be used for custom sequences.
K900+: High-range addresses often reserved for internal Fanuc system functions. How to Access and Modify Keep Relays
Modifying these parameters requires entering "Parameter Write Enable" (PWE) mode first. Enable Parameter Write: Press the MDI button on the control. Press the OFFSET/SETTING function key.
Navigate to the "Setting" page and change PARAMETER WRITE from 0 to 1. Navigate to PMC Maintenance: Press the SYSTEM function key. Press the [PMC] soft key, then [PMCPRM] or [PMC PARAM]. Press the [KEEPRL] or [KEEP RELAY] soft key. Edit the Parameter:
Use the cursor keys to find the specific K-address (e.g., K0005). Bits are numbered 7 6 5 4 3 2 1 0 from left to right. Type the new bit value (0 or 1) and press INPUT. Reset Safety:
Return to the OFFSET/SETTING screen and set PARAMETER WRITE back to 0. Machine-Specific Examples
Turret Rotation (K17.5): On some turning centers, changing this can allow the turret to rotate without returning to home position, reducing cycle times.
Chuck Clamp (K7.6): Can be used to toggle whether the machine checks for a clamp signal before starting the spindle.
Internal Programmer (K17.1): Toggling this bit may allow or prevent on-machine editing of the PMC ladder.
Warning: Keep relay definitions are unique to your machine's MTB. Always refer to the Fanuc Maintenance Manual or the machine-specific electrical manual before making changes to avoid unintended mechanical movements. Fanuc Keep Relay Parameters Overview | PDF - Scribd
In the complex world of Fanuc CNC controls, Keep Relay (K) parameters are essential tools for machine tool builders (MTBs) and maintenance technicians. These non-volatile memory bits are designed to control specific machine behaviors, enable or disable hardware options, and manage complex PLC (Programmable Machine Controller) logic.
The term "exclusive" in the context of Fanuc keep relays typically refers to system-reserved addresses or bits with specific, non-customizable functions that are critical to the CNC's internal operation or safety. Understanding Fanuc Keep Relays
Keep relays differ from standard diagnostic bits because they retain their state—ON (1) or OFF (0)—even after the machine is powered down.
User Keep Relays (K0–K19): These are commonly used by machine builders to define machine-specific options, such as enabling a chip conveyor, bypassing a door interlock for maintenance, or configuring the Automatic Tool Changer (ATC) pattern.
System/Exclusive Keep Relays (K900–K999): These higher-range addresses are often reserved by Fanuc for system-level functions. For example, K928 and K929 may control critical safety circuit interfaces. Unlike user bits, these are often "exclusive" to the system logic and should only be modified under direct manufacturer guidance. Common Uses for Exclusive Logic System Reserved Areas: Addresses reserved by FANUC for
While "exclusive" can refer to reserved system addresses, it also describes logic where certain bits are mutually exclusive.
Safety Interlocks: Exclusive bits may ensure that a tool changer and a spindle cannot operate simultaneously.
Machine Options: MTBs often use keep relays to "lock" or "unlock" specific machine features. For instance, K17.1 might be exclusively reserved for maintenance procedures, such as backing up data or resetting turret positions.
Ladder Access: Certain keep relays, like K19, can be used as an exclusive flag to enable ladder editing or internal programmer functions. How to Modify Keep Relay Parameters
Modifying these parameters requires precise steps to bypass the CNC's internal protection. Enable Parameter Write (PWE): Switch the machine to MDI mode.
Press the OFFSET/SETTING key and locate the SETTING soft key.
Change "PARAMETER WRITE" from 0 to 1. The machine will likely trigger an "ALM 100" (Parameter Write Enable) alarm, which is normal during this process. Access the Keep Relay Screen: Press the SYSTEM hard key.
Use the right arrow (expansion) soft keys until you see PMC, then select PMCPRM or PMC MAINTENANCE. Select the KEEPRL soft key to view the bit table. Input the Data: Navigate to the desired address (e.g., K17). Type the new bit value (0 or 1) and press INPUT.
Crucial: Once finished, return to the SETTING screen and change PARAMETER WRITE back to 0. Troubleshooting "Exclusive" Lockouts
If a keep relay refuses to change or reverts after a power cycle, it is often because:
Ladder Logic Coil: The bit is being written to by a "coil" in the PMC ladder logic. In this case, the software overrides any manual changes.
Mode Restrictions: Some machines require the Emergency Stop to be depressed or the PMC to be stopped before certain system bits can be modified. Fanuc PMC - Keep Relays (K Parameter) Explained in English
The hum of the shop floor was a constant companion for Elias, a veteran maintenance tech. Today, the challenge was a new CNC lathe that refused to engage its bar feeder and parts catcher simultaneously. It was a classic "either-or" scenario, and Elias knew the secret lay within the Fanuc Keep Relays. The Logic of the Keep Relay In the world of Fanuc CNCs, Keep Relays (
parameters) act as the machine’s long-term memory for logic toggles. Unlike volatile signals, these stay set even after the power is cycled. Elias opened the PMCLAD (Programmable Machine Control) screen and found the culprits: K0001.0cap K 0001.0 for the bar feeder and K0001.1cap K 0001.1 for the parts catcher. The Problem: Mutual Exclusivity
The machine builder had programmed these two functions to be mutually exclusive. In the ladder logic, a "Safety Interlock" was written so that if one bit was (ON), the other was forced to (OFF).
The Conflict: The bar feeder required the machine to know it had "material ready," while the parts catcher needed to know the "door was clear." The Overlap: If Elias turned on K0001.0cap K 0001.0 , the ladder logic would automatically "coil off" K0001.1cap K 0001.1 to prevent a mechanical crash. Resolving the Lock
Elias realized he wasn't just fighting a setting; he was navigating the Machine Builder's (OEM) Safety Logic. To make them work together safely, he had to:
Enable Parameter Write: He navigated to the Setting Screen and flipped Parameter Write Enable (PWE) to .
Monitor the PMC: He watched the ladder in real-time. He saw that the "Exclusive" nature was a software "handshake." Adjust the Keep Relay: By toggling a different relay, K012.4cap K 012.4
(the "Integrated Mode" bit defined in the manufacturer's manual), he bridged the two functions.
The machine finally clicked. The bar feeder pushed, the parts catcher waited its turn, and the exclusivity was resolved without a single alarm. Elias turned PWE back to
, cleared the "100 ALARM" (Parameter Write Enable), and watched the first perfect part drop into the bin.
Critical safety functions—like two-hand controls, light curtain responses, or emergency stop resets—are often mapped to dedicated Keep Relays. Making these parameters exclusive prevents a floor operator from setting K123.4 = 1 to bypass a guard switch. Doing so could lead to severe injury.