Solution: Collision Detection and Repeatability Measurement

1. Collision Detection

Collision detection determines whether the robot, its end effector, workpiece or surrounding equipment may come into contact during operation.

Importance

• Protects workers and equipment
• Prevents damage to the robot and workpiece
• Reduces downtime
• Improves path planning
• Supports safer automated operation

Methods

1. Model-based detection — compares robot geometry with the workcell model.
2. Sensor-based detection — uses force/torque, proximity or other sensors.
3. Controller monitoring — abnormal motor torque/current can indicate unexpected contact.
4. Simulation — checks planned paths before executing them on physical equipment.

Robot Model + Workcell Model
            ↓
      Collision Checking
        ↙           ↘
   Collision       Safe path
      ↓               ↓
 Stop/avoid       Execute

2. Repeatability Measurement

Repeatability describes how closely a robot returns to the same position when commanded repeatedly under the same conditions.

It is different from accuracy. A robot can be highly repeatable but consistently offset from the desired target.

Measurement Procedure

1. Select a reference target.
2. Command the robot to the target repeatedly.
3. Record the actual positions reached.
4. Determine the spread of the measured positions.
5. Compare the spread with the specified repeatability.

Conceptually, if the measured positions are $p_1,p_2,\ldots,p_N$, the deviation from their mean position can be evaluated using distance/error measures.

Industrial Importance

Collision Detection

Essential for safe operation in:

• Assembly
• Welding
• Material handling
• Human-robot collaboration
• Automated machining

Repeatability

Important for:

• Pick-and-place
• Assembly
• Welding
• Painting
• Inspection
• Precision manufacturing

High repeatability ensures consistent product quality and reduces rejected parts.

Conclusion

Collision detection protects the robot, workcell and people, while repeatability measurement verifies that the robot can consistently return to commanded positions. Both are critical for reliable industrial automation.