KEVOS® MAKEOS · Mechanics
Rotary Index Table Drive Check (Table Inertia, Motor Torque and Speed, Inertia Ratio, Holding)
For a rotary index table driven by a servo or geared motor, can the motor index it in the time I want, is the inertia match acceptable, and will the drive hold the table against the process force?
Check of a rotary indexing table drive against the motor: table and fixture inertia, index angle, peak speed and acceleration for a cycloidal or trapezoidal move, table and motor peak torques through the reducer, motor speed, the holding torque needed against the process force and the load-to-motor inertia ratio (as the rotary index table sizing tool), against the motor’s peak torque, top speed, your inertia ratio limit and the brake torque multiplied through the reducer.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Table plate mass | kg | Mass of the table plate. |
| Table plate radius | mm | Radius of the table plate. |
| Stations | Number of stations (index positions). | |
| Mass of each fixture and part | kg | Mass of each fixture with its part. |
| Radius of fixture centres | mm | Radius at which the fixtures sit. |
| Index time | s | Time for one index move. |
| Total cycle time | s | Time for a full cycle, index plus dwell. |
| Motion profile | choice | Cam-like cycloidal motion or a trapezoidal velocity profile. |
| Bearing and seal friction torque | N·m | Friction torque of the table bearing and seals. |
| Reducer ratio | Reduction ratio between motor and table. | |
| Reducer efficiency | % | Efficiency of the reducer. |
| Motor rotor inertia | kg·m² | Inertia of the motor rotor. |
| Process force at the fixture radius | N | Tangential process force on a fixture during the dwell. |
| Holding safety factor | Factor on the holding torque. | |
| Motor | ||
| Motor peak torque | N·m | Peak torque the motor can give. |
| Motor top speed | rpm | Highest motor speed. |
| Largest inertia ratio accepted | Largest load-to-motor inertia ratio you accept for good control (reflected through the reducer). | |
| Motor brake torque | N·m | Holding torque of the motor brake (or the drive’s holding torque). |
Method and formulas
- J = ½ M R² + stations × m_f r_f²; index angle 2π ÷ stations; cycloidal ω_max = 2θ ÷ t, α_max = 2πθ ÷ t² (as the rotary index table sizing tool).
- Motor torque = (J α + T_f) ÷ (i η) + J_m α i; motor speed = ω_max i; inertia ratio = J ÷ i² ÷ J_m.
- Holding torque needed = SF × F × r_f; brake holds brake torque × i at the table.
- Example: the motor needs 3.7354 N·m at 1,666.7 rpm with an inertia ratio of 5.88.
Limitations
- Rigid drive; backlash and compliance in the reducer cut the usable stiffness.
- Brake holding taken through the reducer without efficiency loss.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a motor for a dial table
- Find whether a faster index is possible
- Check the brake holds the table during pressing
Who it is for
- Automation engineers
- Machine designers
- Controls engineers
What you get
- Table inertia, speed and acceleration
- Motor torque, speed and inertia ratio
- Holding against the process force
Interpreting the result
- A larger reducer ratio cuts the reflected inertia by its square but raises the motor speed in proportion.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 171, 2284–2290. Topic reference; no source tables or recommended settings are reproduced.
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