By Chris Blaszczyk
Chris Blaszczyk is the Manager of Product Development, Automation Components Div., Misumi USA, Inc.
You have choices on how to precisely move a load in a single axis: actuators, linear guides, slides, stages, or tables will all handle the required motion. To control their function, you may choose among hydraulics, electromechanics, electromagnetics, or other means. And when you use these units as part of a machine, or as part of a piece of equipment, assembly line, or testing device, it’s your choice as to whether to buy or build.
Your decision rests on several factors, as there are specific attributes required of these single-axis devices. They must provide precisely controlled fast motion, while remaining as friction-free as possible, and encounter a minimum of mechanical wear. They must also deliver reliable and repeatable positioning. Today’s linear motion devices let you control the motions more precisely. Plus, newer construction materials better suit the particular needs of various industries.
Dozens of manufacturers offer single axis motion systems in a variety of sizes, styles, and material construction. Several of the most common types of motorized linear actuators are:
• Ball screw driven and ball guided units that handle high thrust, heavy load, precise positioning, and stiffness requirements.
• Ball screw driven and single guided units that are low in cost yet suited for harsh operating environments where contaminants are present.
• Belt driven and ball guided units that offer a long use life and smooth operation, plus high speeds, acceleration, and accommodation of medium payloads.
• Belt driven and slide guided units that require little maintenance but offer high-speed, plus smooth, quiet operation under acceleration.
Various styles of linear motion devices are available today. The decision to make or buy one of these devices hinges on many factors, including the availability of standard or custom product,
the quantities required for the application, the ability of the engineering talent to design and build.
Applications in automotive, appliance, packaging, medical, semiconductor, general assembly and test, and factory automation industries all take different factors into account to select the right operating mode, construction material, performance features, as well as conditions involving ambient noise. Costs are affected by the availability of standard or easily customized product, the quantities required for the application, the ability of the resident engineering talent to design and build, plus the immediacy of need.
The build choice
The decision to build will typically depend on whether you can find an already built unit to suit your application needs. Industries such as medical and semiconductor, where the unit will function in a clean room or other controlled environment, will mandate the use of certain construction grade materials, which may or may not be readily available from traditional component manufacturers. Here, the typical choice would be to build the single-axis unit.
You may find units that meet special material needs, but they may not offer the necessary force, load, travel distances, resolution, deflection, and other mechanical specifications. Other features may be difficult to find as well. These features would include, but not be limited to, the correct size, speed, accuracy, stroke and load-bearing ranges, as well as the finish and lubricant compatibility for certain industries such as food, medical, and semiconductor where particulate migration is a concern.
A purchased unit will often require some minimal design costs. Many companies offer an online configurator that lets you make minor changes for a small fee.
Regardless of the operational mode selected, the choice to build involves calculating the forces, loads, and tolerance build-up for each component. Furthermore, you must calculate the use life of each component, the fit, the function, the durability and the maintenance requirements of each component.
The choice to buy
With a purchased unit, the size, speed, accuracy, positioning repeatability, load, stroke and other feature information are sometimes available at the unit level but not at the component level. Even so, this information can shorten evaluation time. With the decision to build, you often must spend time investigating whether available standard components will properly fit together. A decision to purchase removes this task, saving configuration time.
You must still consider the overall durability of the unit, its lifespan in the particular application, maintenance requirements, and availability. These questions can usually be answered quickly, either by catalog documentation online or, through a phone call to a knowledgeable applications engineer. You must still choose the correct size, speed, accuracy, load, stroke, and motor compatibility for the job.
Suppliers will typically have native CAD files ready to download in various formats to suit your platform. Some will offer an online configuration option that lets you select modifications, often without surcharge, to the standard catalog items.
Thus, you can contain cost, save substantial time, and eliminate outside machining or in-house shop utilization to make modifications before final assembly into the end product or manufacturing operation.
What’s the cost?
Pricing is always a consideration, whether building semiconductors or screwdrivers. The decision to build versus buy takes pricing into account, but in different ways.
When pricing the build of a linear motion unit, there’s the obvious expense of buying individual components separately from various vendors, with the attendant paperwork. To build a single-axis, motor-driven, ball screw actuator with 340 mm base length, 150 mm table width and 12 mm lead screw diameter that will handle a vertical load of about 140 kg, you’ll need a number of components. These components include the ball screw, the guide, support units, table, brackets, and machined aluminum base. Each of these parts will cost approximately $100 to more than $400, based on today’s online published prices. On average, it can cost you a total of more than $2000 to build your unit.
Buying a unit, especially one configured online, is simpler. In many cases, all you need to do is choose the most cost-effective solution. With reputable suppliers, maintenance tasks and purchase costs are generally lower, which can ease budgeting.
A purchased unit will often require some minimal design costs. However, once specifications are entered into an online configurator and you’ve found a suitable CAD file, the procurement process is simple. You will be working with one vendor, one price, one purchase order, and one part number.
In terms of the time required, bear in mind that the build route requires multiple lead times from multiple vendors. Additionally, there’s the internal engineering time for component selection, an assembly drawing, component drawings, order placement, shipping, assembly into production, and inspection. Such a project can typically take several weeks up to several months, depending on the complexity of the chosen components.
Buying, on the other hand, gives you a predictable delivery schedule, which gives you greater control to manage the machine build time. Check, however, to be sure your chosen supplier does not have a large back-order log, which could delay the delivery of your unit.
The decision to build or buy requires an honest assessment of the resident engineering and machine shop resources at your company. In many cases and in most industries, the available products from vendors will save you time and cost, and be a reliable alternative for your linear motion requirements.
Misumi USA Inc.
:: Design World ::
Filed Under: Actuators, Linear motion • slides, Motion control • motor controls