When off-the-shelf servoamps more than meet project needs, custom-designed amps might still be the better choice.
Wood Dale, Ill.
Edited by Robert Repas
Many engineers see the need for custom-designed servoamplifiers when standard off-the-shelf devices fail to meet project needs. Often missed, though, is that custom servoamps might also make sense when off-the-shelf devices contain more features and abilities than an application requires. By not paying for unused capabilities, a custom solution provides the desired performance while actually lowering costs.
Numerous vendors supply servoamplifiers in a bewildering variety of forms and capabilities. Each company seems to have its own idea of what features are best. The variety of options challenges machine builders to identify the product best suited to an application.
Custom servoamplifiers are designed from the start to meet specific machine requirements. While OEMs typically use custom amplifiers to address form, fit, and function, a growing motive for switching to custom systems is cost. So under what conditions should one consider a custom installation?
The servoamplifier market sees two seemingly conflicting trends. As vendors make more products available off-the-shelf, OEMs increasingly view those products as commodity devices rather than specialized electronic equipment. This commodity-centric viewpoint reinforces the perception that the products also have commoditylike prices that drop as competition rises.
Vendors typically counter competition by adding product features rather than reducing prices. They try to make the product appeal to a wider customer base to increase market size and thus boost sales. Prices have not gone up, but neither have they gone down. Manufacturers using the product end up paying for unused features.
Manufacturers often place their prime focus on product costs with only a secondary focus on features and performance. This differs from the situation a few years ago when engineers focused on the feature set. The expectation now is that all products have the same or similar features. Under that scenario, products with the lowest cost get designed into new and retrofit applications.
Many OEMs emphasize component prices in new machines. They want to boost, or at least retain, market share in an increasingly competitive global economy. Manufacturers invest time and resources reevaluating existing designs to reduce cost. Many times retrofit efforts end up with completely new machines. Even in the world of commodity servoamplifiers, designers now look towards innovative options to minimize machine cost. It is exactly for this reason that custom designs can be attractive and, in some cases, necessary.
For example, semiconductor wafer-handling robots typically have three or four servoaxes. Often the robot mounts on a rail along which it moves back and forth between wafer-loading pods or processing stations. One major design consideration in this application is the cabling between the machine controller and the robot. Traditional designs place servoamplifiers within the same area as the machine controller. Long cables run from the amplifiers to the robot motors.
This setup has several problems. The cables are often heavy duty and expensive. They are subjected to continuous bending and so may need to be reinforced.
In this case the solution is simple mount the drives at the robot. A custom-designed multiaxis amplifier can place the axis controls in a single package attached to the robot base. Benefits include lower wiring costs, enhanced reliability, integrated functionality, and added value.
Shorter cables reduce stress and enhance reliability. Shared functionality lowers system cost. For example, the multiaxis amplifier needs only one point of communication between it and the machine controller instead of one point per amplifier as in the traditional case.
The intent of servoamp customization is to add value and reduce costs. If a product is already designed to meet custom requirements, why not go a few steps further to integrate other machine functions into the amplifier? Examples include various machine sensors and input/output signals. Quite often the amplifier makes use of this data. But, even if the servoamp does not use the signals, it can measure, digitize, and send the information to the machine controller. With the interface in the servoamp, wiring and computing costs typically are lower than with standalone controllers.
An example might be a pressure sensor in a wafer-handling robot. Why not put the electronics for the sensor on the custom amplifier instead of building or buying a dedicated monitor? By adding the pressure-sensor electronics to a custom servoamp, OEMs save both unit and installation costs.
One advantage of custom servoamps is that the amp is not constrained by particular packaging philosophies. Rather, packaging is designed according to what is needed. Traditional servoamp packaging includes such niceties as an attractive cover, mounting flanges, and connectors designed to meet any number of standards that may or may not be relevant for the application.
Being free of the traditional packaging constraints allows the engineer to literally think outside the box. Does the unit really need that Mil-Spec connector? What about mounting the amplifier on the actual machine? This second question may be of particular interest because mounting the amplifier where it is needed on the machine may lower wiring costs and improve reliability. The product may also fit into the available or allocated machine space, removing the need (and cost) for an enclosure.
Many products fail simply because their design is driven by perceived, rather than actual, customer needs. Many fine servoamplifiers do an excellent job managing the trade-offs required to make a product meet the requirements of many different applications. However, custom units simply provide exactly what the customer needs no more and no less to meet the true technical and commercial needs of the application.