Improving Mechanical Muscle in Machine Design

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."