The past few blog posts have been regarding the types of bushings and load capacity for the next few posts we will focus on application examples. Linear bushings can be used in a variety of ways to carry out certain functions and move on a desired axis. Many characteristics come into play. Linear bushings are great for low cost solutions or for a more well-balanced linear guide design there are bearings. Choosing bushing style helps narrow down what type of actuator to use, cylinder driven which is low in price or motor driven which is higher in price. For vertical direction guidance, the drive center can be placed at the guide center enabling simple and compact mechanism structure.
In this post we will explain the usage and characteristics of linear bushings through application examples on simplified automation machinery.
XYZ Drive Mechanism
This application is called an XYZ Drive Mechanism. It utilizes synchronous belt drives and a step motor. Synchronous belt drives have various advantages such as quietness, light-weight, low cost, as well as not requiring lubrication maintenance. In 2-axis XY table designs, top Y axis weight is lightened to reduce the load on the bottom X axis. For this, synchronous belt drive is often used for Y-axis design.[Fig.1] shows a typical 3-axis XYZ drive mechanism. As you can see in the outlined drawing, linear guides are used on X-axis with the bearings being supported throughout the entire length of the axis. On the Y and Z axis, linear bushings are used on linear shafts supported on both ends. For driving, synchronous belts and a ball screw are used. All movement is driven by the step motor on each axis converting rotary movement to linear movement via the synchronous belts.
Pallet Transfer Machine, Y-Axis
Below is [Photo 1] which depicts an IC chip pallet transfer machine, a Y-axis application example. The Y-axis motion is converted into reciprocation motion with a synchronous belt, this is where you will see the linear bushings at work on the 2 supported shafts.
Single Axis Robot
[Fig.2] is an application example for a single axis robot. The dual linear bushing guides are widely spaced for good load capacity and accuracy. The synchronous belt drive has light weight and quiet operational characteristics. Vertical inline orientation of the shaft and belt prevents the bushings from rotating, even for this one shaft structure design.
The traveling pulley arrangement in [Fig. 3] below is used for high motor power efficiency and precision positioning.
In order to lift the load (W) in [Fig. 3] by the distance of (S), the rope will need to be pulled up by twice the distance of (S). This requires only half the force of the load (W). If move distance is doubled, motor angular resolution is doubled and the positioning resolution improves. Also, pulley backlash and lost motion is reduced by half. Overall this improves precision. If load is reduced by half, then the motor speed can be doubled for higher motor efficiency and a smaller motor can be used. This improves efficiency. Applying this principal to linear bushings will allow the designer to choose the correct types for high load, high speed or high accuracy.
These are a few of the simplest machines and applications linear bushings are used on. More application examples using linear bushings will be covered in the next post!