In the context of (Programmable Machine Controller) maintenance, Keep Relay parameters
act as non-volatile memory bits that retain their state even after power is turned off. These are primarily used by machine tool builders to enable or disable specific machine options, such as chip conveyors or tool management features. "exclusive"
in the context of these parameters typically refers to two scenarios: exclusive-OR (XOR) logic applied to PMC addresses or exclusive access/protection of parameters. 1. Functional Roles of Keep Relays
Keep relays (K-parameters) serve several critical roles in machine automation and maintenance: Feature Toggling: Enabling or disabling optional equipment like a chip conveyor high-pressure coolant Bypassing Sensors:
Temporarily shielding external alarms or bypassing faulty sensor inputs (e.g., conveyor rotation detection) to keep the machine running. Safety & Interlocks: Managing interlocks such as chuck clamp signals or ATC (Automatic Tool Changer) safety conditions. System Configuration:
Certain "System K" parameters (like K900+) are reserved for internal CNC functions and protected against general modification. 2. Exclusive Logic and Protection
The concept of "exclusive" keep relay parameters appears in technical maintenance documentation in two ways: A. Exclusive-OR (XOR) Operations
In PMC ladder logic maintenance, specific addresses may be processed using Exclusive-OR
operations. For example, a diagnostic address (like R90) might be XOR'ed with a decimal value (like 255) to flip all bits for specific logic evaluations. B. Exclusive Protection (Parameter Hiding)
Modern FANUC controls allow machine builders to set keep relays to "exclusive" or protected states to prevent unauthorized changes: K902.6 / K19.6 (HIDE PMC PARAM):
When set to 1, this "hides" the Timer, Counter, Keep Relay, and Data Table screens entirely. K902.7 / K19.7 (PROTECT PMC PARAM):
When set to 1, it becomes impossible to modify these screens, even if they are visible. 3. How to Access and Modify Keep Relays
To change a keep relay (e.g., turning a feature ON or OFF), follow these standard steps: How to Enable Parameter Write Enable (PWE) on a Fanuc CNC
Since this is a technical topic rather than a consumer product, this "review" evaluates the functionality, necessity, advantages, and potential pitfalls of using exclusive (dedicated) keep relays within FANUC CNC and PMC systems. fanuc keep relay parameters exclusive
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.
Imagine a CNC machining center where:
K12.3 = 1 to enable a high-pressure through-spindle coolant.K12.3 = 0 to disable a safety interlock on a different door, not realizing the coolant logic also reads K12.3.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.
Unlike CNC parameters that directly control numerical values such as feed rates or acceleration curves, Keep Relays are strictly binary (on/off) flags. Their primary and exclusive purpose is to interface with the machine’s PMC (Programmable Machine Controller)—the internal PLC that handles all auxiliary functions like tool changers, coolant pumps, and safety doors.
Each Keep Relay (typically designated as K0.0, K1.2, etc.) is a single bit of memory. When a machine builder writes the ladder logic, they assign these relays to control discrete behaviors. For example:
What makes them exclusive is that they are not readable or writable by the part program (G-code). Standard CNC codes like G10 or system variables cannot modify a Keep Relay. They exist purely for the machine’s internal logic, making them a “private” communication channel between the machine builder and the maintenance engineer, bypassing the operator and the part programmer.
In the world of Fanuc CNC (Computer Numerical Control) systems, parameters are often discussed in broad categories: Axis parameters for servo control, Macro variables for custom calculations, and System parameters for basic configuration. Yet, one class of digital settings stands apart due to its unique functional role and deliberate design philosophy: the Keep Relay. To call these parameters “exclusive” is not an overstatement. They occupy a singular niche—acting as the binary, non-volatile memory cells that govern machine logic, operator behavior, and safety interlocks, all while remaining intentionally shielded from the casual operator. This essay explores the exclusivity of Fanuc Keep Relay parameters in terms of their function, access, application, and strategic importance.
The keyword exclusive here carries three distinct technical meanings. When we say Fanuc Keep Relay parameters exclusive, we are referring to:
| 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 |
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. Machine builder A sets K12
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 a specialized type of internal memory bit used within the Programmable Machine Control (PMC)
to enable or disable specific machine options, logic flows, or hardware configurations without rewriting the PLC ladder. Key Characteristics of Exclusive Keep Relays Non-volatile Storage:
Unlike standard relays, Keep Relays "keep" their state (1 or 0) even after the machine is powered off. Bit-Level Logic:
They are accessed in the PMC as bits (e.g., K0.0 through K99.7). Option Locking:
OEMs often use specific Keep Relays as "exclusive" switches to toggle between different machine features—such as enabling a 4th axis, switching between manual and automatic tool measurement, or locking out certain door interlocks for maintenance. Safety & Interlocks:
Because they are "exclusive," setting one bit often logically inhibits another operation in the ladder to prevent mechanical collisions or unsafe conditions. How to Access and Modify Keep Relays
To view or change these parameters, follow this standard procedure on most Fanuc controls: Enable Parameter Write (PWE): function key. Set "PARAMETER WRITE" to
(ON). The machine will trigger a non-critical alarm; this is normal MachineMetrics Navigate to PMC Maintenance: function key. soft key, followed by Modify the Bit:
Use the cursor to highlight the specific Keep Relay address (e.g., K0005).
Enter the binary value for the specific bit you wish to change (remembering that bit 0 is on the far right and bit 7 is on the far left). Disable PWE:
Return to the Setting screen and change "PARAMETER WRITE" back to
Always consult your machine's original documentation or the OEM ladder diagram before changing Keep Relays, as they are specific to each machine builder and changing the wrong bit can disable critical safety features or machine functions. common K-relay addresses used by specific manufacturers like Haas or Mori Seiki? high-speed skip signals
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.
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
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: