KEVOS® MAKEOS · Mechanics
Linear Move Drive Check (Move Profile, Screw Torque, RMS Torque, Cycle Time)
For a carriage moved back and forth by a motor and screw, how long does each move take, what speed and torque does the motor need, and does it meet my cycle time?
Check of a horizontal screw-driven (or belt-driven) linear axis: the trapezoidal or triangular move profile, move time, peak speed and acceleration force (as the move profile tool), the friction force, the motor speed and the accelerating, running and decelerating torques through the screw lead and efficiency, the RMS torque over an out-and-back cycle with dwells, against the motor’s speed, peak and continuous torque and your cycle time.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Move distance | mm | Length of each move. |
| Speed limit | mm/s | Highest speed allowed for the carriage. |
| Acceleration | mm/s² | Acceleration and deceleration used. |
| Moving mass | kg | Mass of everything that moves with the carriage. |
| Friction coefficient of the guides | Rolling or sliding friction coefficient of the guides. | |
| Dwell at each end | s | Time stopped at each end of the move. |
| Out-and-back cycle time required | s | Time allowed for one move out, one move back and both dwells. |
| Drive and motor | ||
| Travel per motor revolution (screw lead or pulley circumference) | mm | Carriage travel for one revolution of the motor (screw lead, or pulley circumference for a belt). |
| Drive efficiency | % | Efficiency of the screw or belt drive. |
| Motor maximum speed | rpm | Highest speed of the motor. |
| Motor peak torque | N·m | Peak (intermittent) torque the motor can give. |
| Motor continuous torque | N·m | Continuous (RMS) torque the motor can give. |
Method and formulas
- Trapezoidal if L ≥ V² ÷ a: t = L ÷ V + V ÷ a; otherwise t = 2√(L ÷ a); acceleration force = m a (as the move profile tool).
- Friction F_f = μ m g; motor torque T = F × lead ÷ (2π η); motor speed = peak speed ÷ lead.
- T_rms = √(Σ T² t ÷ cycle) with accelerating (m a + F_f), running (F_f) and decelerating (m a − F_f) torques and zero torque in the dwells.
- Example: each move takes 0.7 s; the motor turns 2,400 rpm with 0.52881 N·m peak and 0.2637 N·m RMS over a 2.4 s cycle.
Limitations
- Horizontal axis; on a vertical axis gravity adds to the torque one way and needs a brake.
- Rotor and screw inertia are not included; add their share to the moving mass for a servo sizing.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a motor for a pick-and-place axis
- Check whether a faster cycle is possible
- Pick a screw lead for a linear stage
Who it is for
- Automation engineers
- Machine designers
- Controls engineers
What you get
- Move profile, time and peak speed
- Motor speed and torques
- RMS torque and cycle time against the motor and target
Interpreting the result
- Halving the acceleration time doubles the accelerating torque; a coarser lead trades motor torque for motor speed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 175–180, 155–162. Topic reference; no source tables or recommended settings are reproduced.
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Open the Linear Move Drive Check (Move Profile, Screw Torque, RMS Torque, Cycle Time) calculator
