Linear Motor ConsiderationsBesides the obvious task of matching motor force capabilities to acceleration needs, it is extremely important to be aware of the **HEAT ** generation aspects of the motor in the application. It is therefore vitally important to know how a linear motor is to perform in an application's worse-case scenario.
Determine the following:
- The moving mass (weight of all that moves).
- The stage friction (resistance to motion).
- The required acceleration.
- The required peak velocity.
- Typical sequence of moves (needed to determine heat generation for duty requirements).
- Process dwell times during the typical cycle (needed to determine duty requirements).
- Account for any constant loads that the motor must overcome while at rest (vertical weights, spring loads, cable loads, etc.).
Motor Power Duty :
- Motor power duty is based upon the time the motor is actually working (when current is applied).
- Motor power duty is NOT the % of time the stage is moving !!
As will be shown through an example, it is vitally important to know how the motor is going to be used.
Pick motors for their force capabilities but consider their continuous capabilities with respect to: HEAT - HEAT - HEAT.
Acceleration: Accel/Decel = (motor force ± friction) ÷ weight = g's
(where motor force = K f x applied current)
Example:LEB4 has a peak force rating of 465N (8.2 amps × 56.93N/amp) Typical recirculating bearing friction is » 13.3N (for a 4-puck set) Consider a 34kg moving load (slide + pucks + coil).
Multiply kg × 9.81 to obtain load in Newtons [34kg = 333N]
Accel = (465N force - 13.3N friction ) ÷ 333N load = 1.36g's
& Accel = (465N force + 13.3N friction ) ÷ 333N load = 1.44g's
Note: Frictional forces impede acceleration and help deceleration.