G22 Stored Stroke Limit Check ON G-Code Command: CNC Programming

Introduction

An uncoordinated manual intervention or an unexpected coordinate offset shift during active compensation modes poses a critical production risk. When a tool carrier travels beyond its intended spatial boundaries at rapid traverse, the rotating tool turret can crash directly into the workpiece chuck jaws, tailstock body, or spindle. This severe impact results in a fractured machine spindle, damaged workholding components, and a ruined scrap part that halts the entire shop floor.

To mitigate these physical collision risks, CNC programmers utilize stored stroke limit checks and working area limitations. These functions establish virtual entry-inhibition zones around critical workholding equipment and raw stock. When activated, the control system monitors tool positions in real-time, enforcing automatic deceleration and halting axis travel before the tool tip or toolholder can violate the protected physical boundaries.

Technical Summary

Quick Read

• Program barrier activation and deactivation commands (G22/G23, WALIMON/WALIMOF) in independent blocks to avoid syntax halts.
• Ensure tool length offsets are active before boundary approaches; inactive offsets shift checks to the toolholder, risking chuck impacts.
• Restrict non-motion blocks to fewer than N-2 steps under radius compensation to avoid look-ahead buffer overruns and contour gouging.
• Monitor PLC signals such as Fanuc *TSB to ensure tailstock safety barriers have not been programmatically bypassed during automatic cycles.
• Apply G23 to temporarily disable boundaries when recovering a tool that is trapped inside a prohibited stored stroke zone.
• Establish coordinate system boundaries relative to the active plane (e.g., using G19 YZ plane selection) to match physical fixtures.

Basic Concepts

Stored stroke limit checks restrict the physical traversing envelope of the cutting tool to establish virtual entry-inhibition zones around critical workholding devices and raw stock. By defining the physical boundaries of a workpiece clamped in the chuck or supported by a tailstock, the control system prevents the tool nose from entering these protected envelopes, automatically halting axis movement at the safety boundary. This software-based barrier acts as an electronic guardrail, protecting the CNC machine from human programming mistakes and coordinate offset errors.

Unlike hardware limit switches that trigger only when an axis physically contacts a microswitch, stored stroke limits are monitored continuously by the CNC interpreter. The system evaluates current coordinates against configured boundary parameters. If the system detects a trajectory breach, it decelerates all axes to a stop before a physical collision occurs. This safety envelope can be toggled on or off programmatically during execution to allow tools to enter or exit specific regions, such as during automated part unloading or turret swiveling.

Command Structure

The command structure for safety boundaries relies on specific preparatory codes that must be programmed in independent blocks. The G22 command initiates the stored stroke limit check, establishing the chuck and tailstock boundaries as active entry-inhibition zones. The G23 command deactivates the limit check, canceling the active boundaries to allow axis movement into the protected envelopes for tool changes or raw stock loading.

Depending on the manufacturer and the active coordinate system, boundaries can be defined dynamically via G-code parameters or pre-loaded system variables. When programming boundaries directly, absolute coordinate addresses define the positive and negative limits of the protected envelope. The control system evaluates these coordinate values against the active G-code state, adjusting the internal verification parameters whether the machine is operating under G20 inch input or G21 metric input standards.

G-Code Syntax

; Fanuc Syntax
G22 ;
G23 ;
G22 Xp_ ;
; Siemens Syntax
G25 X_ Y_ Z_ ;
G26 X_ Y_ Z_ ;
WALIMON ;
WALIMOF ;
WALCS1 ;
WALCS0 ;
; Mitsubishi Syntax
G22 ;
G23 ;
G22 X_ Z_ C_ I_ J_ K_ ;
G22.1 X_ Y_ Z_ I_ J_ K_ ;

Command Parameters

Brand Applications

Fanuc

Fanuc controls utilize stored stroke limit checks to establish a virtual safety zone around workpiece chucks and tailstocks. The system initialization defaults are governed by Parameter No. 3402 Bit 7, which dictates whether G22 is active at power-on. The controller also references Parameter No. 3401 Bit 7 to interpret axis designations under the active G-code system.

Programmers activate the stored stroke check by commanding G22 in an independent block. To disable boundaries for tool changes or parts catcher operations, a standalone G23 command is programmed. During active tool nose compensation, the area coordinates can be specified using G22 Xp_ where Xp represents the coordinate axis.

Warning: Programmers must closely monitor the PMC tailstock barrier selection signal *TSB. If the PMC outputs a *TSB value of 1, the tailstock barrier is deactivated even if G22 is active, which can result in a physical crash if the tailstock is moved under auxiliary commands.

Siemens

Siemens SINUMERIK controls manage axis boundaries in the Basic Coordinate System (BCS) and Workpiece Coordinate System (WCS) using machine data values. Geometry axis switches and zero-offset resets are configured via machine data MD10604 and MD10710.

Lower and upper boundary limits are defined in separate NC blocks using G25 and G26 commands respectively. These boundaries are activated globally via WALIMON and deactivated via WALIMOF. For coordinate-specific limits, WALCS1 through WALCS10 can be programmed to select up to ten WCS-based limitation groups, while WALCS0 cancels them.

Warning: Toggling working area limitations when tool length compensation is inactive causes the check reference to shift from the tool tip to the toolholder reference point. This offset displacement can cause the tool turret to cross physical boundaries and crash during rapid movements.

Mitsubishi

Mitsubishi CNC systems use stored stroke limits to establish entry-prohibited ranges for the machine axes. The axes boundaries are configured using Parameter #8204 for the negative-side limits and Parameter #8205 for the positive-side limits.

The chuck and tailstock barriers are enabled by G22 and disabled by G23, programmed alone in independent blocks. Stored stroke limit II is activated by commanding G22 X_ Z_ C_ I_ J_ K_ to specify absolute boundary coordinates. On machining centers, G22.1 activates travel checks while G23.1 cancels them.

Warning: If positive and negative boundary parameters are set to the same value (such as 0), the controller locks out all travel on that axis. Operators must complete all axis reference position returns before verifying boundaries to validate barriers.

Brand Comparison

Technical Analysis

A comparative analysis of safety boundaries reveals fundamental differences in how Fanuc, Siemens, and Mitsubishi interpret and execute coordinate constraints. Fanuc controls integrate G22 safety barriers directly with the programmable machine controller (PMC) interface signals. By linking the tailstock barrier to the PMC signal *TSB, the PLC program can programmatically enable or disable the safety zone on-the-fly. This allows the tailstock to advance or retract during parts catcher cycles without triggering coordinate alarms. In contrast, Siemens and Mitsubishi do not utilize this direct PMC interface signal linkage for routine G22 operations, relying instead on explicit G-code states or manual parameter configuration.

The boundary checking method represents another major architectural variance. Fanuc and Siemens evaluate limits primarily by assessing the final programmed endpoint of a move. Mitsubishi, however, implements a path-passing stroke check when machine parameters #12057 and #8179 are enabled. Rather than checking only the endpoint coordinate, the Mitsubishi interpreter calculates the entire toolpath trajectory during rapid traverse (G00) and cutting interpolation (G01/G02/G03). If the path vector intersects a prohibited boundary at any point, the controller halts travel and triggers Program Error P452 before the axis starts moving.

Interpreter look-ahead handling also differentiates these systems. Fanuc imposes look-ahead pre-read limits under active cutter radius compensation, where programming more than N-2 consecutive non-motion blocks (such as consecutive G22 area settings) exhausts the buffer. This preprocessor limitation forces the Fanuc system to generate perpendicular error vectors that gouge the profile. Siemens avoids this preprocessor buffer constraint entirely by managing limits as system variables ($AC_WORKAREA_CS_LIMIT_PLUS and $AC_WORKAREA_CS_LIMIT_MINUS) and G-group 3 preparatory commands (WALIMON/WALIMOF) which do not occupy motion pre-read buffers.

Program Examples

Fanuc Example

O1001 ;
G28 U0 W0 ;
G54 ;
G22 ;               ; Activate stored stroke limit check
G00 X100.0 Z50.0 ;  ; Move to start position
T0101 ;
G01 Z-20.0 F0.2 ;   ; Feed path near Chuck
G23 ;               ; Deactivate limit check to permit chuck clearance
G00 X150.0 Z100.0 ; ; Retract to safe area
M30 ;

Dry Run: The program starts by homing axes via G28 and selecting workpiece coordinates. Command G22 activates the safety boundaries around the chuck. The tool approaches to X100.0 Z50.0, then performs a linear cut to Z-20.0. When G23 is read, the controller disables stored stroke checks, permitting the turret to retract to X150.0 Z100.0 without triggering overtravel alarms when traversing close to the workholding equipment.

Siemens Example

N10 G291 ;          ; Enter ISO Dialect Mode
N20 G54 ;
N30 G25 X-80.0 Z30.0 ; ; Define lower working area limits
N40 G26 X80.0 Z330.0 ; ; Define upper working area limits
N50 WALIMON ;       ; Switch ON working area limitations
N60 T1 D1 ;         ; Tool change and offset activation
N70 G00 X60.0 Z100.0 ; ; Rapid approach tool tip
N80 G01 Z-50.0 F0.15 ; ; Linear machining
N90 WALIMOF ;       ; Switch OFF working area limitations
N100 G00 X100.0 Z350.0 ; ; Retract past upper limits
N110 M30 ;

Dry Run: The control enters ISO Dialect Mode with G291 and establishes G54 coordinates. G25 and G26 specify the lower and upper limits in the Basic Coordinate System (BCS). WALIMON activates the safety limits. The tool executes rapid positioning and cuts to Z-50.0. The controller monitors the tool tip against limits. WALIMOF deactivates the working area limitation, allowing the tool to retract beyond the G26 limits (Z350.0) for a safe tool change without triggering Alarm 12080.

Mitsubishi Example

O2001 ;
G28 X0 Z0 ;
G54 ;
G22 X120.0 Z200.0 I-120.0 K-200.0 ; ; Activate stored stroke limit II
G00 X80.0 Z50.0 ;   ; Approach workpiece
T101 ;
G01 Z-30.0 F0.2 ;   ; Linear interpolation
G23 ;               ; Cancel stored stroke limit II
G00 X150.0 Z100.0 ; ; Safe retraction
M30 ;

Dry Run: The program initiates axis homing and coordinate system selection. The command G22 X120.0 Z200.0 I-120.0 K-200.0 specifies Stored Stroke Limit II boundaries (positive limits at X120/Z200, negative limits at I-120/K-200) and activates the check. The tool approaches and cuts. The controller evaluates the tool path trajectory against parameters #8204 and #8205. Finally, G23 cancels the limits, letting the tool retract to X150.0 Z100.0 without triggering program error P452.

Error Analysis

Application Note

A hard collision resulting in a fractured spindle occurs when tool length compensation offsets are cleared during a geometry axis switchover. On Siemens controls, if machine data MD10604 is configured to 0, the active working area limitations are deactivated automatically during a geometry axis switch. When this occurs, and tool offsets are cleared (such as executing a tool change without applying the proper D-edge offset), the control shifts its envelope check from the tool tip to the toolholder reference point. During a rapid traverse approach (G00), the tool carrier can travel beyond intended spatial boundaries, crashing the turret directly into the workpiece chuck or raw stock.

To prevent this, programmers must coordinate boundary parameters with active offsets. On Mitsubishi controls, toggling G188 mid-run shifts the G-code mode from lathe format to machining center format. This shifting changes the interpretation of G22/G23 from Group 04 (Barrier check) to Group 00 (Subprogram call). If the programmer attempts to define safety zones using Lathe syntax under G188 Machining Center mode, the parser will split blocks like G23.1 X100.0 ; into two separate lines, executing the cancellation first and moving the tool unprotected. Operators must verify that all axis reference position returns are completed and checkpoints are configured in range "c" on the HMI to ensure Chuck barriers are validated before cutting.

Related Command Network

• G23: Deactivates stored stroke check boundaries to allow the tool to traverse into safety or tool change zones.
• G25 / G26: Defines the lower and upper working area limits in the basic coordinate system on Siemens controls.
• G22.1 / G23.1: Activates and deactivates the travel stroke check function before axis movement on Mitsubishi machining centers (M-system).
• G40 / G41 / G42: Controls cutter radius compensation, which interacts with look-ahead buffers during G22 execution.

Conclusion

Implementing stored stroke limits requires careful synchronization of coordinates, parameters, and tool offsets. Protecting the physical machine from catastrophic collisions demands that programmers verify look-ahead buffer sizes and always validate boundary statuses after tool changes. Ensuring safety barriers are active before rapid approaches remains the single most effective practice to eliminate scrap parts and machine downtime.

FAQ

Why does the CNC machine lock out all axis travel when G22 is activated

This travel lockout occurs when the positive and negative boundary parameters are set to the same value, such as 0, or if the prohibited zone is configured on the outside. To resolve this, operators must update Mitsubishi parameters #8204 and #8205 (or equivalent) to valid coordinate limits and perform axis homing to re-establish the reference origin.

Can I program G22/G23 in the same block as tool movement commands

No, programming G22 or G23 alongside motion coordinates or auxiliary M-codes violates format rules, causing the parser to halt with errors. Programmers must write G22 and G23 as standalone statements in independent blocks to ensure the interpreter activates or deactivates safety boundaries before the machine initiates travel.

Why did my tool turret crash into the chuck jaws even though G22 was active

This crash typically happens when tool length compensation is disabled, which forces the controller to evaluate the boundary check from the toolholder reference point instead of the tool tip. Operators must ensure that correct tool offsets are active in the program registers and verify boundaries using graphic check dry runs before running automated turning cycles.