Electric cylinder also known as industrial linear actuator, is one of the linear motion solution which need high speed drive with big force. Designing an electric cylinder for a pressing machine involves several key considerations, including force requirements, stroke length, speed, precision, and control. Below is a step-by-step guide to designing an electric cylinder for a pressing application:
1. Define Application Requirements
Force (kN or lbs): Determine the maximum pressing force required.
Stroke Length (mm or inches): How far the cylinder must extend/retract.
Speed (mm/s or in/s): Desired linear speed during operation.
Duty Cycle: Continuous or intermittent operation.
Precision (mm or inches): Required positioning accuracy (e.g., ±0.01mm).
Environment: Temperature, dust, moisture, etc.
2. Select Electric Cylinder Type
Electric cylinders come in different configurations:
Ball Screw Driven: High precision, high force, moderate speed.
Lead Screw Driven: Lower cost, lower efficiency, suitable for lighter loads.
Belt Driven: High speed, lower force capability.
Linear Motor: Ultra-high speed and precision, expensive.
For pressing machines, ball screw-driven electric cylinders are commonly used due to their high force and precision.
Servo Motor: High precision, dynamic control, ideal for pressing applications.
Stepper Motor: Lower cost, suitable for simpler applications with open-loop control.
AC/DC Motor with Encoder: For basic speed/position control.
Key Motor Parameters:
Torque (Nm or lb-in) – Must meet force requirements.
Speed (RPM) – Must match required linear speed.
Power (kW or HP) – Depends on force and speed.
Force Calculation:
F=2π×Motor Torque×Efficiency/Lead of Screw
Where:
F= Linear force (N)
Lead of screw = Distance traveled per revolution (mm/rev)
Efficiency (~90% for ball screws)
4. Mechanical Design Considerations
Frame & Housing: Must withstand pressing forces without deflection.
Guide Rails: Linear bearings or profile rails for smooth motion.
End Stops: Mechanical limits for overtravel protection.
Couplings & Mounting: Ensure proper alignment between motor and screw.
5. Control System
PLC or Motion Controller: For automated pressing cycles.
Force & Position Feedback: Load cells or pressure sensors for closed-loop control.
HMI Interface: For operator input and monitoring.
Example Pressing Sequence:
Rapid approach (high speed, low force).
Pressing (controlled force/speed).
Dwell time (holding force).
Retract.
6. Safety Features
Overload Protection: Torque limits in servo drives.
Emergency Stop: Cut-off power in case of failure.
Mechanical Brakes: Prevent back-driving in vertical applications.
7. Example Calculation
Scenario:
Required Force: 10 kN
Stroke Length: 200 mm
Speed: 50 mm/s
Ball Screw Lead: 10 mm/rev
Desired Positioning Accuracy: ±0.02 mm
Steps:
Motor Torque Calculation:
Torque=F×Lead/2π×Efficiency=10,000N×0.01m/2π×0.9≈17.7Nm(Add 20-30% safety margin → ~22 Nm required.)
Motor RPM:
RPM=Linear Speed (mm/s)×60/Lead (mm/rev)=50×60/10=300RPMRPM=Lead (mm/rev)Linear Speed (mm/s)×60=1050×60=300RPMMotor Selection:
A servo motor with ≥22 Nm torque and ≥300 RPM (e.g., 400W-750W servo motor with gearbox if needed).
8. Advantages of Electric Cylinders in Pressing Machines
Precise Force & Position Control (vs. hydraulic/pneumatic).
Energy Efficient (no constant fluid pressure needed).
Clean & Low Maintenance (no oil leaks or air compressors).
Programmable (flexible press profiles).
9. Potential Challenges
Higher initial cost than hydraulic/pneumatic.
Heat generation in high-duty cycles (may require cooling).
Limited force compared to large hydraulic systems.
Conclusion
An electric cylinder for a pressing machine should be designed based on:
• Force, speed, and stroke requirements.
• Precision and control needs.
• Proper motor and screw selection.
• Integration with safety and feedback systems.
For heavy-duty applications (e.g., >50 kN), hydraulic systems may still be preferable, but electric cylinders excel in precision pressing (e.g., electronics assembly, medical device manufacturing).
