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Siemens SINUMERIK Controller
Program/G-code · Intermediate · 30-120 minutes
Siemens 75255 - RCTR: unreachable position interpreter
Alarm 75255 fires when the NCK block interpreter detects a target position that cannot be reached within the machine's configured workspace limits or kinematic constraints. This occurs during block preprocessing before actual axis motion is commanded, indicating either invalid program coordinates, misconfigured machine parameters, or violated soft limits in the active channel.
Siemens 75255 - RCTR: unreachable position interpreter
RCTR: unreachable position interpreter
On block interpretation a non-approachable position is detected: Control reaction: Interpreter stop Alarm display.
Root Cause Summary
Alarm 75255 fires when the NCK block interpreter detects a target position that cannot be reached within the machine's configured workspace limits or kinematic constraints. This occurs during block preprocessing before actual axis motion is commanded, indicating either invalid program coordinates, misconfigured machine parameters, or violated soft limits in the active channel.
Safety
Causes and Fixes
Access Diagnostics menu: HMI → Diagnosis → Actual Values → Channel [%1] → Axis Positions. Record current machine coordinates and compare against programmed block target.
Navigate to Parameters → Machine Data → 3600 (Axis-Specific) series. Verify MD 36100 (positive limit) and MD 36110 (negative limit) for the axis triggering the alarm. Check if programmed position falls outside this range.
Do not blindly increase soft limits without verifying physical machine safety and end-stop hardware clearance.
Review active G10 offset registers (SD 42000-42199 depending on offset number) and verify coordinate transformation is not compounding position error. Cross-check with MD 28050 (zero offset enable).
If limits are correctly set, edit the NC program to move within legal boundaries, or adjust soft limits via Parameters → Machine Data if machine geometry has been verified.
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