What the C150 alarm means

The robot detected that a joint is approaching its mechanical/software limit and initiated a protective stop; this is the most frequently seen protective stop in production cells. In our Universal Robots service archive this alarm on CB3 / e-Series (UR5/UR10/UR16/UR20) systems shows up constantly, and the first on-site inspection almost always locates it.

Most common causes

  • Taught points programmed too close to a joint limit
  • Path blends swinging the joint past the safe margin
  • Wrong TCP/mounting settings making the inverse kinematics pick a bad elbow configuration
  • Mechanical hardstop moved or worn
Field note: The first cause is the most common in the field — check it first, then work through the rest.

Step-by-step field fix

  1. Jog away from the limit in joint mode (toward the safe direction)
  2. Reteach the offending via point with more joint margin
  3. Check TCP configuration and mounting settings
  4. Review blend radii near the limit zone
  5. If the joint limit itself is wrong, verify the mechanical zero and calibration
Safety first: For Universal Robots c150, this alarm family points at arm motion control: after a reset the arm can move unexpectedly, and anyone inside the working envelope is at strike and pinch risk. What you can check yourself first is Jog away from the limit in joint mode (toward the safe direction); the arm working envelope handling is not a DIY job.

How we diagnose motion alarms on site

Universal Robots c150 belongs to the motion & path family. On Universal Robots c150 the failing stage is joint-integrated drives (motor, drive and harmonic reducer in one joint) on the UR control box (CB3 / e-Series) - the gap between command and execution: trajectory planning, joint limits, singularities, following error and mechanical resistance. We start reading Universal Robots c150 at the PolyScope event and alarm pages; codes carry a C prefix (C15x, C5x, C7x).

The chain involved in Universal Robots c150 runs: program command -> trajectory planner -> joint targets -> servo execution -> actual position feedback -> deviation compare.

The clearest field clue for Universal Robots c150 is Taught points programmed too close to a joint limit; the discriminator is this test: The most valuable judgement on motion alarms is separating software from mechanics. We take the fixture off and re-run the same path below 10% speed: if it is clean unloaded and slow, the problem is mechanical - over-heavy tooling, shifted centre of gravity, or a joint that already has drag; if it alarms even unloaded and slow, look at program points, frame calibration and whether the path crosses a singular region. No instruments needed, and it removes half the wrong turns.

Field notes on this page cover Universal Robots c150 (Protective Stop — Position Close to Joint Limits); written by the Henghuan repair team, updated 2026-10-01.

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Related Motion & Path alarms

C153 — Protective Stop — Position Deviates from Path C154 — Protective Stop — Position in Singularity C155 — Protective Stop — Robot Cannot Maintain Position C157 — Protective Stop — Collision Detected
Same family: this code belongs to the Motion & path alarms family - the page collects all Motion & path-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for Kawasaki · Staubli · Epson and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the Universal Robots c150 alarm mean?

The robot detected that a joint is approaching its mechanical/software limit and initiated a protective stop; this is the most frequently seen protective stop in production cells. In our Universal Robots service archive this alarm on CB3 / e-Series (UR5/UR10/UR16/UR20) systems shows up constantly, and the first on-site inspection almost always locates it. Universal Robots c150 sits in the motion & path family; on our work orders the highest-frequency trigger for this code is "Taught points programmed too close to a joint limit".

QCan I clear a Universal Robots c150 alarm myself?

Whether Universal Robots c150 clears on its own depends on the outcome of "Jog away from the limit in joint mode (toward the safe direction)". Finish the flow with "If the joint limit itself is wrong, verify the mechanical zero and calibration" to confirm Universal Robots c150 - do not skip it. If that step is clean, the second most frequent cause on Universal Robots c150 is "Path blends swinging the joint past the safe margin". Do not chase takt through a repeating Universal Robots c150. Left alone, motion & path faults tend to graduate from repairable to must-replace.

QFor motion alarms like Universal Robots c150, can you triage remotely first?

The commonest causes we see on Universal Robots c150 are "Taught points programmed too close to a joint limit, Path blends swinging the joint past the safe margin, Wrong TCP/mounting settings making the inverse kinematics pick a bad elbow configuration", so we stock the van against those. For Universal Robots c150 specifically, we carry mechanical and configuration items: grease, limit switches, drag-chain segments, encoder cables and the parameter sheets for common reducers. For Universal Robots c150, motion alarms can often be narrowed remotely first, so an on-site visit is not always immediate. Before we roll, tell us what Universal Robots c150 shows on the PolyScope event and alarm pages; codes carry a C prefix (C15x, C5x, C7x) and what the machine was doing - phone or video triage is free.

This page on Universal Robots c150 was compiled from actual repair records of the Henghuan Robotics repair team. Alarm notes are our own summary for troubleshooting reference only and may vary with controller and software version — please consult Universal Robots documentation or contact us if in doubt. Henghuan is an independent service provider, not affiliated with or endorsed by Universal Robots.