Using linear bushings correctly.

Linear bushing applications in simplified automatic machinery - Example 1

The characteristics of linear bushings discussed so far are summarized below:

Low-cost, balanced, linear guide bearings (good cost effectiveness).
A small coefficient of friction makes it easy to select an actuator (low-cost cylinder types or medium-cost motor types).
Use of a timing belt enables a quiet and lightweight drive mechanism.
In the case of a vertical guide, a simple, compact structure can be achieved through a center of gravity drive mechanism.

The characteristics and methods of use for linear bushings will be explained through their applications in simplified automatic machinery.

(1) Stepping motor and timing belt drive

The advantages of a timing belt drive are quietness, lightweight, low cost, no need for lubrication, etc. In the case of a 2-axis XY table, efforts are made to reduce the weight of the upper Y-axis in order to ease the load on the lower X-axis motor. For this purpose, a timing belt is often used on the Y-axis.

a) [Fig. 1] is a typical 3-axis XYZ drive mechanism.

A slide guide is used on the X-axis. Linear bushings are used on the Y-axis and the Z-axis. For the drive mechanism, timing belts and ball screws are used.

Click image to enlarge.

b) [Photo 1] is an example of a Y-axis application on an IC chip transfer unit. The Y-axis has been converted into a reciprocating movement by using a timing belt.

Click image to enlarge.

c) [Fig. 2] is an example of a 1-axis robot application with the following features:

1. It uses 2 linear bushings with long spans for a higher load allowance and improved precision.
2. The timing belt and the shaft are positioned parallel to each other and one above the other. This restricts rotation into linear bushings, often present in one shaft structure.
3. The timing belt drive provides lighter weight and quietness.
4. Using the principle of moving pulleys for the positioning of belts and pulleys ([Fig. 3]), motor power efficiency and positioning accuracy are improved.

Principle of moving pulleys

In order to lift the balance weight W at distance S [Fig. 3], it is necessary to pull a rope twice the distance S, but with force that is one half of the balance weight W.

High precision - The moving distance is double.

<1> This improves positioning accuracy at the minimum resolution of motor rotation.
<2> This reduces backlash or lost motion errors of the pulley by half.
<3> The motor is driven at high rotation speeds (twice as fast), resulting in higher motor efficiency.

High efficiency - The load is a half.

<4> A small capacity motor is sufficient for the drive
(eliminating the need for reduction gears, etc.).

Click image to enlarge.

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