What the C157 alarm means
Joint torque monitoring detected a collision; the robot stopped immediately to protect itself, the tooling and the environment. This is a high-frequency ticket for our Universal Robots repair team, and on CB3 / e-Series (UR5/UR10/UR16/UR20) systems one inspection usually identifies the fault.
Most common causes
- Real collision with workpiece, fixture or person
- Collision sensitivity set too low for the application
- Payload settings wrong so normal torque looks like an impact
- Mechanical binding in a joint
Step-by-step field fix
- Inspect the tool and surroundings for damage first
- Back the robot off the collision point in freedrive or joint mode
- Verify payload and mounting settings
- Adjust collision sensitivity only after confirming the settings are right
- If the alarm fires with no contact, check joint backdrivability and calibration
How we diagnose motion alarms on site
Universal Robots c157 belongs to the motion & path family. On Universal Robots c157 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 c157 at the PolyScope event and alarm pages; codes carry a C prefix (C15x, C5x, C7x).
The chain involved in Universal Robots c157 runs: program command -> trajectory planner -> joint targets -> servo execution -> actual position feedback -> deviation compare.
First check whether Universal Robots c157 only appears at one pose - A six-axis arm near wrist extension or near axis-5 zero has a Jacobian approaching singularity: tiny tool moves demand huge joint rates, and the controller either reports following error or the arm snaps through. When the report is alarms at one position and clean on another path, suspect the singular region first. The fix is not raising speed limits but routing around it: move the part, add an intermediate point, or pass the region in joint interpolation.
Field notes on this page cover Universal Robots c157 (Protective Stop — Collision Detected); written by the Henghuan repair team, updated 2026-10-01.
Real Field Case
Machine: UR UR16e (2021)
Symptom: A UR16e frequently raised C157 (collision detected) with no visible interference.
What we did: We reviewed the sensitivity settings and payload parameters, found a wrong payload configuration causing false alarms, corrected the payload and recalibrated.
Result: The false alarms stopped after the parameter fix and it ran normally; about 2 hours.
If you can't fix it, reach our engineers directly
Share the alarm code, machine model and the operating condition at the moment of the alarm. Our engineers are highly experienced with Universal Robots c157, and remote diagnosis (phone/video) is completely free.
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Related Motion & Path alarms
C150 — Protective Stop — Position Close to Joint Limits C153 — Protective Stop — Position Deviates from Path C154 — Protective Stop — Position in Singularity C155 — Protective Stop — Robot Cannot Maintain PositionFrequently asked questions
QWhat does the Universal Robots c157 alarm mean?
Joint torque monitoring detected a collision; the robot stopped immediately to protect itself, the tooling and the environment. This is a high-frequency ticket for our Universal Robots repair team, and on CB3 / e-Series (UR5/UR10/UR16/UR20) systems one inspection usually identifies the fault. Universal Robots c157 sits in the motion & path family; on our work orders the highest-frequency trigger for this code is "Real collision with workpiece, fixture or person".
QCan I clear a Universal Robots c157 alarm myself?
Whether Universal Robots c157 clears on its own depends on the outcome of "Inspect the tool and surroundings for damage first". Finish the flow with "If the alarm fires with no contact, check joint backdrivability and calibration" to confirm Universal Robots c157 - do not skip it. If that step is clean, the second most frequent cause on Universal Robots c157 is "Collision sensitivity set too low for the application". Do not chase takt through a repeating Universal Robots c157. Left alone, motion & path faults tend to graduate from repairable to must-replace.
QFor motion alarms like Universal Robots c157, can you triage remotely first?
The commonest causes we see on Universal Robots c157 are "Real collision with workpiece, fixture or person, Collision sensitivity set too low for the application, Payload settings wrong so normal torque looks like an impact", so we stock the van against those. For Universal Robots c157 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 c157, 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 c157 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.
The notes on Universal Robots c157 were summarized by the Henghuan Robotics repair team from on-site service. The alarm interpretation is our empirical summary for troubleshooting reference and may vary by controller and software version — please check Universal Robots documentation or contact us with questions. Henghuan is an independent service provider, not affiliated with or endorsed by Universal Robots.