In a perfect world, every robot program would run start to finish without a hitch. But in real production environments, things happen: a part slips, a safety light curtain trips, an operator hits the E-stop. Now the robot is stuck mid-process—and your only option is to restart from the beginning.
That’s a frustrating and often unnecessary limitation. A well-designed robot program should be able to restart gracefully, either from where it left off or from the last known safe step. This is especially important for collaborative robot (cobot) applications, where human-machine interaction is frequent and interruptions are common.
Here’s how to design smarter, restartable robot logic that improves uptime, reduces operator headaches, and keeps your automation running efficiently. For more practical automation solutions, explore our real-world robotics projects.
Why Restarts Are a Challenge in Robot Logic
Most robot platforms remember the robot’s position, but not the state of the process. When a program is paused or stopped midway—especially in systems with multiple steps (pick, place, press, unload, etc.)—the robot has no built-in awareness of what has already been done.
If the operator presses “Start” again, the program might:
- Try to pick up a part that’s no longer there
- Repeat a placement action that’s already been done
- Skip safety checks or clash with other automation
For this reason, most systems force a restart from the top—which can waste time, re-handle good parts, or risk collisions. Discover how our advanced cobot implementations solve these challenges.
4 Essential Strategies for Restartable Robot Programs
Strategy 1: Track Program State with Step Counters or Flags
The most reliable way to enable restarts is to track your program’s progress explicitly. Use a global variable such as CurrentStep or ProcessStage to represent what phase the robot is in:
CurrentStep = 1 // Ready for pick CurrentStep = 2 // Part picked CurrentStep = 3 // Placement complete
Each section of your program should update this value when completed. On startup, you can read the variable and jump to the appropriate section:
If CurrentStep = 1 Then Call StartFromBeginning() ElseIf CurrentStep = 2 Then Call StartFromPlaceStep() EndIf
Pro Tip: Combine with manual confirmation (HMI input or physical button) to prevent unsafe restarts after critical stoppages.
Strategy 2: Design Clear Checkpoints or Restart Zones
While you can build restart logic for every possible line of code, that’s usually overkill—and hard to maintain. Instead, define key restartable checkpoints where it’s safe and logical to resume:
- After part acquisition and verification
- Following vision alignment completion
- Post-unload to a tray or conveyor
- Before entering high-risk processes (presses, welding)
Label these checkpoints clearly in your operator interface and documentation. For implementation examples, see our cobot project portfolio.
Strategy 3: Use Operator Prompts and Recovery Options
In real-world deployments, operators need guided decision-making after stoppages. Implement intuitive prompts at restart:
"Robot stopped during placement. Press A to restart from pick Press B if part placed manually"
These can be delivered through:
- Cobot-native dialog systems (URCap, TM Flow)
- External HMIs or button panels
- Simple input confirmation boxes
Always include manual recovery tools:
- Gripper/vacuum reset buttons
- Sensor bypass options (with confirmation)
- Manual position adjustment modes
Strategy 4: Implement Persistent State Storage
For environments with frequent power cycles or E-stops, use persistent memory to maintain state across reboots:
// At program end or key milestones:
WritePersistent("LastStep", CurrentStep)
// On startup:
CurrentStep = ReadPersistent("LastStep")
This ensures continuity even after unexpected shutdowns. Systems like industrial cobots with PLC integration excel at this.
Benefits of Restartable Program Design
- 45-75% faster recovery after E-stops or faults
- 60% reduction in scrapped parts from redundant operations
- Operator empowerment with 24/7 self-recovery capabilities
- 5-15% OEE improvement through minimized downtime
- Reduced technical support calls during off-hours
When operators trust automation as a reliable tool rather than a fragile black box, adoption rates and productivity soar. Explore more benefits in our case studies.
Implementation Checklist: Building Restart-Ready Systems
- Define critical process states (minimum 3-5 milestones)
- Implement step-tracking variable with global scope
- Establish safe restart zones avoiding mid-motion points
- Develop operator decision trees for common failure scenarios
- Integrate persistent storage for power-cycle resilience
- Create HMI visualization of current process state
- Test failure modes (simulated E-stops, part jams)
Conclusion: Engineering for the Real World
Restartability isn’t a luxury—it’s what separates robust production systems from fragile prototypes. By implementing these strategies:
- You transform disruptive stoppages into minor pauses
- Operators become empowered partners in automation
- Systems gain resilience against inevitable real-world disruptions
Remember these core principles:
- Track process state as rigorously as robot positions
- Design checkpoints before complex or irreversible actions
- Communicate clearly through operator prompts
- Assume failures will occur and plan recovery paths
For more insights on building industrial-grade automation, visit our homepage or browse our advanced robotics projects. Ready to implement restartable logic in your next project? Our engineers specialize in robust cobot implementations that withstand real-world challenges.
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