UR Robot Not Moving But No Error – Motion Authorization & Brake Release Diagnostic Guide

When a Universal Robots system refuses to move without showing an active alarm, the first assumption is usually:

• controller failure
• oftware corruption
• teach pendant issue

Field diagnos is says otherwise in most cases.

The controller is often running normally.
The robot simply never reachesfullfull motion authorization state.

This is why a UR robot can:

• oot normally
• load programs correctly
• respond normally on PolyScope
• how no major popup alarm

while still refusing any physical movement.

In real production environments, this condition is usually tied to:

• afety recovery state
• ervo enable interruption
• rake release failure
• remote/local mode conflict
• ayload configuration mismatch
• internal synchronization instability

Unlike major controller faults, these conditions often produce:

• o red alarm
• o Protective Stop popup
• o fatal shutdown message

Controller Running vs Robot Ready

One of the most common troubleshooting mistakes:

“No error means the robot is healthy.”

Not true on UR systems.

Controller operation and motion authorization are two separate layers.

A robot only becomes movable after all validation layers complete successfully:

• afety validation finished
• ervo bus energized
• joint brakes released
• motion planner initialized
• ayload model accepted
• remote/local control synchronized

If any layer remains incomplete, the robot may stay stationary without showing a critical fault.

PolyScope Status Bar: The Hidden Diagnostic Clue

The PolyScope bottom status bar often shows exactly where motion authorization stopped.

Important field pattern

If system remains stuck at:

• Starting
• Braking
• Recovery

motion authorization is usually blocked internally.

Common Symptoms

Typical field behavior:

• teach pendant fully responsive
• o visible popup alarm
• rogram loads normally
• auto mode refuses to start
• manual jogging unavailable
• Freedrive inactive
• reboot temporarily restores motion
• hesitation before movement

Usually not controller failure.

Usually incomplete motion authorization.

Most Common Causes

1. Safety Recovery State Still Active

The visible alarm may disappear while the internal safety state machine still blocks motion.

Typical causes:

• incomplete E-stop reset
• guard-door acknowledgment missing
• afety relay timing mismatch
• afety PLC handshake interruption

Field behavior

Robot appears “ready”, but motion remains locked internally.

Pro Diagnostic Tip

Verify stable 24V safety supply first.

Recommended safety supply range:
23.5V to 24.5V

Intermittent voltage instability can silently block motion authorization without triggering major alarms.

Very common in:

• older control cabinets
• overloaded 24V rails
• hared safety power circuits

2. Brake Release Failure

UR robots use electrically released joint brakes.

If one brake fails to release correctly, global motion authorization may be denied.

Typical symptoms

• robot feels mechanically rigid
• one axis remains locked
• repeated clicking noise during startup
• PolyScope status stuck at “Braking”

Freedrive as a Physical Diagnostic Tool

Freedrive is one of the fastest field-level checks.

It helps separate:

• rake-release issue
• ervo-enable issue
• higher-level control blockage

Important field rule

If robot stays rigid during Freedrive, inspect:

• rake power
• ervo enable chain
• joint hardware

before replacing controller hardware.

3. Remote Control / Local Control Conflict

UR systems may reject motion commands when operation modes become inconsistent.

Very common after:

• PLC integration changes
• Dashboard Server modifications
• Ethernet/IP updates
• PROFINET configuration changes
• remote mode activation

Field behavior

Robot appears operational but ignores motion commands.

e-Series 3-Position Enabling Device Check

On e-Series teach pendants using 3PE switch, motion is only allowed when the switch remains in middle position.

Very common during commissioning or maintenance testing.

4. Incorrect Payload or Center of Gravity Configuration

UR robots continuously calculate:

• joint torque demand
• gravity compensation
• tartup torque validation

If payload or CoG values become inaccurate, the controller may silently reject motion authorization.

No major alarm required.

Common Symptoms

• hesitation before movement
• random motion timeout
• movement possible only at low speed
• motion restored after payload reduction

Very common after:

• EOAT replacement
• TCP modification
• tooling changes without recalibration

5. Internal Communication Instability

Minor synchronization failures can block motion without fatal alarm.

Typical symptoms

• motion restored after reboot
• random startup failure
• delayed joint initialization
• inconsistent servo startup timing

Diagnostic Tip

Check grounding integrity carefully.

Recommended ground voltage difference:
below 1V

Ground noise above this level may disrupt:

• ervo synchronization
• internal communication stability
• rake authorization timing

Log Viewer: Why “Gray Messages” Matter

Many motion-blocking conditions appear only as informational entries.

Not critical alarms.

Look for:

• Brake Release Timeout
• Safety State: Recovery
• Motion Not Allowed
• Servo Enable Failed
• Joint Initialization Delayed

Important field rule

No active alarm does not mean no abnormal condition exists.

Motion Authorization Diagnostic Workflow

Step 1 — Observe PolyScope State

Check whether system remains at:

• Starting
• Braking
• Recovery

This often reveals a blocked motion layer immediately.

Step 2 — Verify Safety Chain

Inspect:

• E-stop circuit
• afety relays
• guard interlocks
• afety PLC outputs

Step 3 — Test Freedrive

Use Freedrive to verify:

• rake release state
• ervo authorization
• ingle-joint lock condition

Step 4 — Validate Payload Settings

Confirm:

• ayload mass
• center of gravity
• TCP configuration

Step 5 — Review Informational Logs

Focus on:

• recovery-state messages
• rake timing
• ervo startup interruption

Gray log entries usually matter more than expected.

High-Frequency Misdiagnoses

• unnecessary teach pendant replacement
• assuming “No Alarm = No Fault”
• replacingfullfull controller too early
• ignoring payload changes
• ignoring informational logs

These mistakes commonly create repeated downtime and long troubleshooting cycles.

Final Diagnostic Perspective

When a UR robot refuses to move without an active alarm, the problem is usually not random.

In most production environments, the controller itself is operational while the motion state machine remains blocked somewhere between:

• afety validation
• ervo enable
• rake release
• ayload verification
• motion synchronization

Fast diagnos is comes from identifying which layer failed to authorize motion.

Not from blind hardware replacement.

FAQ

1.Why does my UR robot stay at “Starting” or “Braking”?

Usually incomplete servo initialization or brake-release authorization failure.

2.Why does Freedrive not work even without alarms?

Freedrive requires:

• uccessful safety validation
• rake release authorization

If either layer fails, the robot may remain rigid without major fault messages.

3.Can incorrect payload settings stop robot movement?

Yes.
Incorrect payload or Center of Gravity values can block motion authorization.

4.Why is there no red alarm on the controller?

Many UR motion-blocking conditions appear only as:

• informational states
• gray log entries

not critical alarms.