Tangential Drives

Tangential drives consist of a pulley or pinion which, when rotated, exerts a force on a belt or racks to move a linear load. Common tangential drives include pulleys and cables, gears and toothed belts and racks and pinion.

Tangential drives permit a lot of flexibility in the design of drive mechanics, and can be very accurate with little backlash. Metal chains should be avoided since they provide little or no motor damping.

Tangential Drives permit a lot of flexibility in the design of drive mechanics. In this application a movie camera is being modified to expose each frame under computer control in order to generate special effects. A step motor is installed to index a 38 mm (1.5 inches) frame in 200 msec.

Machine Objectives:

• Index one frame within 200 milliseconds
• Indexer must be compatible with BCD interface
• Fast rewind and frame indexing

Motion Control Requirements:

• Little to no vibration at rest -- Stepper
• Minimum setting time
• Preset and slew moves

Application Description

A movie camera is being modified to expose each frame under computer control for the purpose of generating special effects. A motor will be installed in the camera connected to a 1/2-inch diameter, 2-inch long steel film drive sprocket and must index one frame in 200 milliseconds. The frame spacing is 28 mm (1.5").

Application Solution:

In this application, the move distance and time are known, but the required acceleration is not known. The acceleration may be derived by observing that, for a trapezoidal move profile with equal acceleration, slew and deceleration time, 1/3 of the move time is spent accelerating and 1/3 of the total distance is travelled in that time (a trapezoidal move).

It is determined that the acceleration required is 107.4 rps2 at a velocity of 7.168 rps. Assume that the file weighs 1 oz. and total film friction is 10 oz-in. The rotar, sprocket and film inertia is calculated to be 0.545 oz-in/sec2. Solving the torque formula indicates that the motor for this application must provide 11.9 oz-in to drive the film and pulley.

An indexer is selected to be connected to a BCD interface in the camera electronics. Preset and Slew modes on the indexer are then controlled by the camera electronics to provide fast rewind and frame indexing.

Product Solutions:

• Indexer/Drive - ZETA6104
• Motor - OS21B Motor