CHAPTER 15 APPENDIXES
15-14
Capacity Selection Calculation
15
15.5 Capacity Selection Calculation
15.5.1 Type of Mechanical System
The mechanical system driven by a variable speed motor includes the following types.
Mechanism Features
Ball screw (direct coupling)
Used for a relatively short distance and accurate positioning.
The motor is connected with the ball screw via a coupling and no
play is included.
Ball screw (geared)
A reduction gear is included so that the torque transmitted to the
mechanical system becomes large.
Because of a gear backlash, compensation measures are
necessary.
Rack & Pinion
Used for positioning of a relatively long distance (such as carrier
drive).
Because a π value is included in each pinion rotation,
compensation measures are necessary.
Timing belt (conveyor)
Has a relatively large degree of freedom when compared with chain.
Mainly for small loads.
Because a π value is included in the traveling distance of each
pulley rotation, compensation measures are necessary.
When applying the servo system to a mechanical system, take care of the following points.
(1) Reduction ratio
Use nearly at the rated speed (maximum rotation speed) of the motor to take advantage of the
servomotor power. The continuous output torque at the maximum rotation speed is smaller than
the rated torque.
(2) Preload torque
The load torque of a preloaded screw is large while the rigidity is increased. For the friction torque
caused by the preload, refer to the specifications of the ball screw.
(3) Retention torque
The servomotor keeps outputting the retention force in the stopping state of a hoisting machine.
Use of a retention brake is recommended if the time allows.
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