Improving Mechanical Muscle in Machine Design

The Thoughtful Combination of Mechanical and Electronic Componentry Usually Provides the Best Motion Solution

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Over the several years we've surveyed our audience regarding its particular uses of mechanical components in its machine designs, the respondents are quite consistent about the chief challenges they confront while facing relentless pressure to improve machine performance, flexibility and reliability. They rank these challenges by importance thusly:

1.    Integration of electronic and mechanical components
2.    More precision/less drift
3.    Faster updates/better synchronization (this was fourth on list in 2009)
4.    Integration of digital safety with motion (third in 2009)
5.    Migration to more electronic components and away from mechanical
6.    Combining electronics with pneumatics and/or hydraulics
7.    Migration to more electronic components and away from pneumatic and hydraulics

SEE ALSO: Integration Tops Motion Challenges

Our audience often reminds us that an entirely electronic solution isn't always the best solution. In a recent article, "From A to B With Mechanical Control," Tekno, a builder of conveyors and material handling solutions, told us that cost is one reason the company sometimes turns to mechanical motion control. A mechanical solution usually is cheaper initially, and it can cost less to operate because of lower support costs and quicker time-to-repair. "That's a consequence of the simplicity of the system and the ability to spot and diagnose problems quickly," said CEO Larry Mustread. "I know that it's going from point to point. If it starts losing that movement from point to point, it's easy to pick up that I'm getting wear somewhere."

Similarly, Darek Tkacz, chief mechanical engineer at M&R Printing, a screen printing machine builder, said his company's initial solution for a demanding indexing requirement involved a direct-drive approach with a high-end servo motor and gearbox. The latter had less than 0.05° of backlash — an accuracy needed because it had to position a carousel within a stationary fork to lock it. For a 40 in. diameter carousel, the location had to be accurate to within less than 0.002 in. Though the direct-drive approach worked and offered higher throughput, it was significantly more expensive than the pneumatic method. So for its lower-range machine, "instead of a direct drive, we installed a crank-type index design," Tkacz explained. "The crank is connected through a link to a capture fork, so rotary motion is converted into linear motion back and forth."

He said the crank design boosts the throughput of some presses by about 50%, with little increase in price over the older technology, partly because the crank arm method is more forgiving in what it demands from a gearbox. "We've been able to choose a gearbox that can have 10 arc-min backlash and we can still achieve our linear accuracy for the indexing."

Aerotech's AGR Series Repeatable. Repeatable   
AGR Series motorized rotary worm-gear-drive stages claim accuracy to 20 arc sec, with 8 arc sec bi-directional repeatability, 30 rpm maximum speed, and 360° continuous or optional limited travels. Tilt error motion is 10 arc sec, axial error motion is 5 µm, radial error motion is 10 µm, and maximum axial load is to 425 kg. Apertures are available at 50–200 mm diameter. Vacuum-compatible versions for pressures to 10-6 torr are available.
(412) 963-7470
Baldor Electric's Dodge Maxum XTR concentric reducer Concentric Reductions   
Dodge Maxum XTR concentric reducer with precision, carburized, ground gearing meets AGMA Q11 standards and AGMA 2301 cleanliness specifications. O-ring sealing and steel shims eliminate gasket creep. The reducers are available in nine case sizes, with torque ratings 9,800–575,000 in-lb torque. Reducer accessories include internal high-capacity backstops, shaft-driven fans, scoop motor bracket package, or top motor mounts.
Baldor Electric
(479) 646-4711
Bimba Manufacturing's Original Line Electric Thruster Full Thrusters   
Original Line Electric Thruster (OLET) guided electric cylinder combines the Original Line Electric (OLE) cylinder with the strength of the legacy T/TE pneumatic thruster, with speeds to 24 in./s and thrust to 350 lb general-duty and heavy-duty versions offer three bearing options.

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