A Smaller World for Linear-Motion Components

--by Wayne M. Greer, SKF Motion Technologies

The miniaturization of linear-motion components is much more involved than simply reducing the dimensions of guideways, slide units, ball bearings, or ball and roller screws. In addition to saving space, smaller components must be designed, specified, and manufactured for exacting precision and full integration to achieve optimal end-product performance. In electronics applications, the trend grows toward finer structures and smaller components with increasingly higher degrees of integration. The same picture has emerged in mechatronics and the assembly of printed-circuit boards, as well as in the medical-equipment field. Other linear-motion applications utilizing smaller components range from semiconductor packaging equipment to systems for aligning and splicing fiber optic cables.

While enabling technology is at the heart of industry’s capability to “downsize” components and realize heightened levels of performance, miniaturization of components for linear systems has advanced due to a variety of additional influencing factors. Among them:

• “Smaller” often translates to “lighter,” and components whose designs shed superfluous weight can achieve higher dynamics, require less power, and operate more effectively and efficiently.
• Smaller “design envelopes” for system components have forced designers to “fit more into less.” (One of our customers, a manufacturer of measuring machines, needed to find room in a confined installation compartment for a second measuring sensor. This could only be done by slimming down the linear guides and integrating components.)
• The “miniaturization” of parts to be positioned by linear systems has rippled to the development of smaller machines (and components) to handle the tasks.

A spiraling demand across-the-board for so-called “smaller solutions” has resulted in a variety of linear-system component innovations, which have been making the most of minimal situations.

For example, our company has introduced Miniature Profile Rail (MPR) Guides to satisfy applications demanding maximum component density in minimum installation space. These compact stainless-steel rail guides can provide precise linear positioning, smooth operation, high load-carrying capacity, high stiffness, and unlimited stroke for a wide variety of linear motion applications in the semiconductor, precision mechanics, mechanical engineering, microassembly, electronics, and medical industries, among others.

The smallest rail width (so far) for these miniature profile rail systems is 7mm, which corresponds with a proportional reduction in the size of the slide units. Whereas slide units (for rail size 15) are 71mm long and 47mm wide, their smaller counterparts now measure just 23.5mm long and 17mm wide and offer a weight reduction factor of approximately 20X. Gothic arch grooves at the raceway contacts of the MPR Guides enable the slides to sustain loads from any direction.

We also manufacture miniature slides in four basic sizes (7, 9, 12, and 15) with widths ranging from 17mm to 32mm and lengths ranging from 26mm through 165mm. Made of stainless steel, they can provide high carrying capacity, extremely smooth motion, and precision guidance for applications in fiber optics (aligning/splicing cables), medical, pneumatics, semiconductor, microassembly, and electronics industries, among others. Depending on the application, running accuracies of 0.002mm over a stroke of 100mm can be achieved.

There are also miniature linear ball bearings, rolled ball screws and roller screws available. The latter category includes recirculating roller screws with grooved rollers with extremely small (1mm) leads. The design of these particular screws promotes fine resolution, minimum drive torque, and high mechanical advantage to minimize input torque and increase resolution. The screws’ roller contacts make assemblies simple, robust, and reliable, all in a relatively smaller package; and their many strong contact points contribute to heavy load-carrying capacity, high rigidity, and long life.

Whenever and wherever miniature linear-system components are involved, potential challenges may arise unless recognized and prevented before they can cause a problem. And, as with their larger counterparts, smaller components will be susceptible to all the usual external forces, including vibration and contamination. System and component designs should compensate to minimize possible risks.

In general, potential problems can be averted at the outset by taking advantage of the design and engineering expertise offered by experienced linear-system manufacturers. Such professional support can prove invaluable in designing customized integrated solutions to fit (small or otherwise) application requirements.