Motion System Design

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During machine builds, most design engineers in charge think first about needed components, and then look for custom parts to complete the system. This is when the real work begins — drawing, sizing, measuring, and specifying the complete list of components. It's also when much precious time and money is spent completing designs.

How the big guys design

As a result, during the past 20 or so years, large machine builders have invested heavily in standardization. Through the creation of standardizing departments, these companies have increased value-adding standard engineering projects to streamline every aspect of machine design, build, and procurement to reduce overall system cost and lead time while optimizing the design itself. It's been effective: Large machine builders that invested in such departments have cut project cycles in half compared to those of 10 or 20 years ago. And other machine builders have followed suit, creating modular concepts for their machines, to increase consistency and ease of doing business with customers.

At smaller companies

On the other hand, many small to medium machine builders cannot afford special standardization departments, and they find it increasingly difficult to compete in the world of automated machinery. Often these companies cannot even dabble in standardization — especially when they produce a range of unique automation machines that do not lend themselves to commonality between designs.

Traditionally, these builders used in-house machining for linear shafts, guides, rollers, rotary shafts, locating pins, posts, washers, and so on. But now, as builder operations contract and expand, many smaller builders must part with talented individuals during slow business periods, only to be short on staff when the next big job is assigned. So, after components are designed, machine builders must often decide between purchasing components and manufacturing them in-house. If it's the latter, to keep the shop from going idle, builders often manufacture other components internally too, even if this increases overall machine price. The only drawback is that this can make it difficult to meet project budgets, as internal machine shops (and their staff, maintenance, paperwork, and space requirements) can be costly.

Another approach: Order out

In factory automation, there are three major component types. Custom designs are drawn by an engineer and ordered. Standard designs are typically stocked and sold at high volumes. Configurable components, a newer option, consist of basic designs that can be highly modified with plug-in parameters. The latter are most often specified and ordered online.

It works like this: Machine builders pick a basic unit — whether coupling, ballscrew, or other device — and then work within parametric standards used in industry to finalize that piece of their design. These components are made to order, so it's possible to purchase small quantities or even one component at a time. Pricing and lead times are competitive with high-volume catalog components. It's an approach that gives smaller machine builders the efficiency of large builders, and it fits well with increasingly common lean automation supply chains that aim to tailor component output to design engineer requests.

Let's say a machine builder uses an angle plate on almost all machine build projects. Well, the engineer cannot just create a standard and stock those angle plates, because hole locations and overall size will likely vary from project to project. But with configurable components, the engineer can go online, set parameters, use CAD configurators to place holes and size dimensions for angle plates, download native CAD files (with part number, cost, and shipping time) and put them right into their assemblies when the physical parts are delivered. Calculating specifications and drawing custom components are eliminated, and multiple configuration specifications meet a variety of industry needs. So, design engineers simply configure the component they need, and eliminate most extra custom components. Parametrical design typically makes components fit together with little effort.

Approach comparison

Typically, after the conceptual stage, design engineers calculate forces and motion needed for machine operability and performance, and then size motors and select as many of the final components as possible. This is when the work really begins; design engineers must address all the issues of connecting custom-designed and manufactured components. This stage is also where most efficiency is lost.

With configurable components, design engineers reduce custom details. This in turn reduces compatibility issues and performance compromises associated with standard components that are suitable, but don't offer the fit needed for a quality machine build.

One example

Say an engineer installs configurable linear shafts and linear bushings, and then integrates configurable ballscrews with machined ends that fit standard shaft supports. Well, a nut bracket can be designed to fit the nut, and the height specified to even fine increments. This allows the ballscrew to adjust for shaft assembly height, eliminating custom components there. Plates and brackets can also be configured and machined to engineer specifications, all the way down to the location and size of machined holes. Once the motor is sized, the engineer can select a coupling with holes that have inner diameters of almost any practical size, in either inch or metric styles. Hybrid couplings and sizing components (linear shafts in 1-mm length increments, for example) are also possible; washers and collars, too, have configurable ODs and IDs, thickness, and other dimensions.

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Japan uses this approach

In Japan, there is a famous saying that the nail that sticks up gets hammered down. Well, the Japanese value placed on uniformity extends into their industry. It's one of the major differences between machine builds from Japan and those from the States: Japanese machines are very modular. Their factory automation is also very uniform in design, look, feel, performance, and compatibility — so much so, that machines can look as if the same engineering team designed them. Typical builders there have small work cells, a few design engineers, and no stockroom of parts or machine shop at all. Their design engineers use configurable components from common suppliers. In sharp contrast, nearly every U.S. machine is unique — even those from the same company or team of engineers. Design engineers often use a group of major component suppliers.

There are advantages and disadvantages to each approach, but Japanese machines are definitely more efficient. They put in use the configurable components we discuss here.

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