How to select linear actuators for lab instruments

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How to select linear actuators for lab instruments

  1. 1. Jim Monnich Engineering Manager Selecting Electromechanical Drive Trains for Lab Instruments
  2. 2. Electromechanical: Balancing the Tradeoffs Repeatability Accuracy Cost Efficiency Duty Cycle Speed Resolution
  3. 3. So where do we start with selection…
  4. 4. Think about your PET! Precision Expected Life Throughput Special
  5. 5. Resolution Repeatability Accuracy Velocity Control Precision
  6. 6. Mechanical Efficiency Mechanical Wear Resistance Contamination Resistance Maintenance Expected Life
  7. 7. Speed Capacity Maximum Acceleration Frequency Response Duty Cycle Throughput
  8. 8. Force Density Material Cost Implementation Cost Travel Length Special Considerations
  9. 9. Ball Screw • Threaded rod and matched ball nut with recirculating bearings in the screw. The bearings improve efficiency and increase duty cycle. Lead Screw • Simple threaded rod and machined nut with sliding interface. In some cases the nut is preloaded against the screw to reduce backlash. Timing Belt • Timing belt attached to a carriage with cogged pulley. Most simple kind of motion. Rack & Pinion • Machined gear that moves a linear rack back and forth or the gear moves as the rack is stationary. Linear Motor • A row of magnets interfaces with an electromagnetic carriage to move a load in a linear direction. 5 Common Linear Drive Mechanisms
  10. 10. Technology Image Example Resolution Repeatability Accuracy per 300mm Velocity Control Ball Screw Good (~ 5 µm) Good (~ 5 µm) Good (~ 15 µm) Good (~ 1%) Lead Screw Good (~ 5 µm) Moderate (~ 20 µm) Moderate (~ 30 µm) Moderate (< 2%) Timing Belt Low (~ 50 µm) Low (~ 100 µm) Low (~ 250 µm) Low (< 5%) Rack & Pinion Moderate (~ 20 µm) Moderate (~ 50 µm) Low (~ 150 µm) Moderate (< 3%) Linear Motor Excellent (< 1 µm) Excellent (~ 1 µm) Excellent (~ 5 µm) Excellent (<1 %) Precision
  11. 11. Technology Image Example Resolution Repeatability Accuracy per 300mm Velocity Control Ball Screw Good (~ 5 µm) Good (~ 5 µm) Good (~ 15 µm) Good (~ 1%) Lead Screw Good (~ 5 µm) Moderate (~ 20 µm) Moderate (~ 30 µm) Moderate (< 2%) Timing Belt Low (~ 50 µm) Low (~ 100 µm) Low (~ 250 µm) Low (< 5%) Rack & Pinion Moderate (~ 20 µm) Moderate (~ 50 µm) Low (~ 150 µm) Moderate (< 3%) Linear Motor Excellent (< 1 µm) Excellent (~ 1 µm) Excellent (~ 5 µm) Excellent (<1 %) Always needed Precision
  12. 12. Technology Image Example Resolution Repeatability Accuracy per 300mm Velocity Control Ball Screw Good (~ 5 µm) Good (~ 5 µm) Good (~ 15 µm) Good (~ 1%) Lead Screw Good (~ 5 µm) Moderate (~ 20 µm) Moderate (~ 30 µm) Moderate (< 2%) Timing Belt Low (~ 50 µm) Low (~ 100 µm) Low (~ 250 µm) Low (< 5%) Rack & Pinion Moderate (~ 20 µm) Moderate (~ 50 µm) Low (~ 150 µm) Moderate (< 3%) Linear Motor Excellent (< 1 µm) Excellent (~ 1 µm) Excellent (~ 5 µm) Excellent (<1 %) Needed for Scanning Applications Precision
  13. 13. Technology Image Example Mechanical Efficiency Wear Resistance Dirt Resistance Maintenance Ball Screw Excellent (80 – 95%) Good (Rolling) Moderate (Seale) Moderate (Lubrication) Lead Screw Low (10 – 50%) High (Sliding) Moderate (Sliding) Moderate (Preload Adj.) Timing Belt Excellent (80-90%) Excellent (Tension) Excellent (Harsh env.) Good (Belt Tension) Rack & Pinion Good (70-80%) Moderate (Pinion) Moderate (Jamming) High (Lubrication) Linear Motor Excellent (Non- contact) Excellent (Cables) Poor (Need Cover) Excellent (None) Expected Life
  14. 14. Technology Image Example Mechanical Efficiency Wear Resistance Dirt Resistance Maintenance Ball Screw Excellent (80 – 95%) Good (Rolling) Moderate (Seale) Moderate (Lubrication) Lead Screw Low (10 – 50%) High (Sliding) Moderate (Sliding) Moderate (Preload Adj.) Timing Belt Excellent (80-90%) Excellent (Tension) Excellent (Harsh env.) Good (Belt Tension) Rack & Pinion Good (70-80%) Moderate (Pinion) Moderate (Jamming) High (Lubrication) Linear Motor Excellent (Non- contact) Excellent (Cables) Poor (Need Cover) Excellent (None) High Efficiency = Long Life Expected Life
  15. 15. Technology Image Example Mechanical Efficiency Wear Resistance Dirt Resistance Maintenance Ball Screw Excellent (80 – 95%) Good (Rolling) Moderate (Seal) Moderate (Lubrication) Lead Screw Low (10 – 50%) High (Sliding) Moderate (Sliding) Moderate (Preload Adj.) Timing Belt Excellent (80-90%) Excellent (Tension) Excellent (Harsh env.) Good (Belt Tension) Rack & Pinion Good (70-80%) Moderate (Pinion) Moderate (Jamming) High (Lubrication) Linear Motor Excellent (Non- contact) Excellent (Cables) Poor (Need Cover) Excellent (None) Environment Control Expected Life
  16. 16. Technology Image Example Speed Accel / Decel Frequency Response Duty Cycle Ball Screw Moderate ( < 1.5 m/s) Good (~ 3 G) Good (30 – 50 Hz) Excellent (100%) Lead Screw Low ( < 0.5 m/s) Moderate (~2 G) Low (0 – 30 Hz) Low (50%) Timing Belt Excellent ( > 10 m/s) Good (>3 G) Low (20 – 30 Hz) Excellent (100%) Rack & Pinion Excellent ( > 10 m/s) Good (>3 G) Low (20 – 30 Hz) Excellent (100%) Linear Motor Excellent ( > 10 m/s) Excellent (> 5 G) Excellent (50 – 80 Hz) Excellent (100%) Throughput
  17. 17. Technology Image Example Speed Accel / Decel Frequency Response Duty Cycle Ball Screw Moderate ( < 1.5 m/s) Good (~ 3 G) Good (30 – 50 Hz) Excellent (100%) Lead Screw Low ( < 0.5 m/s) Moderate (~2 G) Low (0 – 30 Hz) Low (50%) Timing Belt Excellent ( > 10 m/s) Good (>3 G) Low (20 – 30 Hz) Excellent (100%) Rack & Pinion Excellent ( > 10 m/s) Good (>3 G) Low (20 – 30 Hz) Excellent (100%) Linear Motor Excellent ( > 10 m/s) Excellent (> 5 G) Excellent (50 – 80 Hz) Excellent (100%) Long Moves Throughput
  18. 18. Technology Image Example Speed Accel / Decel Frequency Response Duty Cycle Ball Screw Moderate ( < 1.5 m/s) Good (~ 3 G) Good (30 – 50 Hz) Excellent (100%) Lead Screw Low ( < 0.5 m/s) Moderate (~2 G) Low (0 – 30 Hz) Low (50%) Timing Belt Excellent ( > 10 m/s) Good (>3 G) Low (20 – 30 Hz) Excellent (100%) Rack & Pinion Excellent ( > 10 m/s) Good (>3 G) Low (20 – 30 Hz) Excellent (100%) Linear Motor Excellent ( > 10 m/s) Excellent (> 5 G) Excellent (50 – 80 Hz) Excellent (100%) Short, Quick Moves Throughput
  19. 19. Technology Image Example Force Density Material Costs Needs to Implement Travel Length Ball Screw Excellent Moderate Motor, Bearings (linear / rotary) Moderate ( ~5 feet) Lead Screw Excellent Good Motor, Bearings (linear / rotary) Low (~3 feet) Timing Belt Moderate Excellent Motor, Bearings (linear / rotary), Gearbox Excellent ( ~30 feet) Rack & Pinion Moderate Moderate Motor, Bearings (linear), Cable Management Excellent (> 40 feet) Linear Motor Low High Bearings (linear), Feedback, Cable management Excellent (> 40 feet) Special Considerations
  20. 20. Looking at the Pros and Cons ……
  21. 21. Precision Ball Screws When • High precision applications with moderate speed (< 1 m/sec). • Applications requiring very good repeatability (micron level) • Applications requiring high force densities. Difficulties • Requires precision alignment of screw to path of travel. • Requires precision angular contact bearings assembly design. • Requires a precision coupling, which will require precision alignment of screw to motor shaft. • Selecting the right lubricant. • Can be noisy. • Maintenance.
  22. 22. Lead Screws When • For low speed and low duty cycle applications. • Non-back driving applications. • For periodic adjustment applications Difficulties • Low efficiency, requires larger motors. • May have resonance issues. • Requires precision screw alignment • .
  23. 23. Timing Belt and Pulley When • For High speed applications • When long life maintenance free operation is important • Lower precision application >100um Difficulties • Has periodic error due to out- of-round precision of the pulleys. • Has long lead error caused by pitch diameter precision. (This can be compensated). • Must have some form of belt tensioning. • Care must be taken in designing pulley bearing system to handle loading.
  24. 24. Rack and Pinion When • Ideal for long travel applications. • High speed motion. • Typically lower precision. Difficulties • Alignment of the rail must be precise, especially in tooth height. • Can be noisy, especially spur type. • Hard to remove backlash • Precision is impacted by tolerance of pinion.
  25. 25. Linear Motor When • High speed. • Very high precision. • No backlash. • Exceptionally low following error. • Fast move and settle times. • . Difficulties • Difficult to use in vertical applications. • Magnetic field can be problematic • Less Force density compared to most other drive trains. • Requires linear feedback for operation, this drives up over all cost. • Can be Expensive.
  26. 26. Parker Can Help!!! Work with Parker and achieve the right balance: Precision LifeThrough- put
  27. 27. Standard Products – not inclusive Precision Industrial
  28. 28. Custom Engineered Solutions
  29. 29. High Throughput Market: Lab Automation Application: High throughput screening Solution: Multi-axis belt driven, Cartesian robot
  30. 30. Partner with Parker

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