Dear Colleagues,
Electrical and mechanical engineering professionals often lose track of important issues in each other’s field. Mechatronics is an excellent example of multidisciplinary engineering often combining state-of-the-art mechanical and electrical engineering with control and instrumentation thrown in.
Some tips follow for the mechanical guys in creating the best design taking consideration of the electrical issues (adjusted from Dan Throne’s note). This will help optimise the operation with lower operating and maintenance costs. As I chewed on this, I am sure there will be some additional comments and indeed, disagreements – so please send comments through and I will highlight them in the next blog.
Top Electrical Considerations for mechanical professionals
Create a clean mechanical design. Although mechanical engineers think that the automation and electrical engineers can often compensate for problems in the mechanical areas (which they can do); this can be challenging and obviously isn’t the best approach. A “clean” mechanical design means a strong, rigid frame so that there is stability no matter what motion the machine goes through. Rigid bearings and support should be utilised where motors are mounted on machines. This avoids the inevitable result of shafts being sheared. Other issues are avoiding unnecessary vibration / motors placed in best position so that electric cables aren’t in awkward places waiting for operators to trip over them / machine guarding placed appropriately / heat from motors and electronics is dealt with appropriately and vibration is minimised. And naturally - components can be easily (and safely) accessed for maintenance.
Directly couple the motor to the load. Older designs (some a few hundred years old) were based on an ac motor powering a machine line shaft to which were connected gearboxes, pulleys and other mechanical devices. Try and simplify this by individual servo motors coupled directly (and as close as possible) to the load. This minimises additional failure points, costs of pulleys, gears, sprockets and maintenance costs and reduces costs dramatically (with no more irritating backlash problems with gears).
Utilise electronic gearing and camming. Today you can create a “virtual electronic line shaft” (as Dan Throne so aptly puts it). This can electronically synchronise all drives and motors on the machine thus eliminating the mechanical line shaft (with no mechanical backlash – yay!). Motion precision can be made incredibly high.
Design green for energy efficiency. Today energy costs are ramping up dramatically and people are considerably more environmentally aware of the need for energy savings. Sizing of motors needs to be done just right with careful consideration of acceleration requirements of the load; the size of the mass to be moved and precision requirements for the acceleration and deceleration. If you undersize, you may strain your drives; if you oversize you waste energy by drawing too much power. With larger machines, regenerative power supplies can feed excess power (e.g. due to the deceleration process of the motors) back into the electricity grid (and not waste it as heat as in older drives).
Use HMIs/ SCADA and PLCs effectively for troubleshooting. As an example of how to do this properly, one only needs to think of the irritating paper jams on your photocopier. Nowadays (well, on ours at least), the diagnostics on the little display panel (HMI) shows how to fix these in an idiotproof way (and written so that even an orang utan can remedy the problem). A mechatronics designer can incorporate in the HMI easy-to-action diagnostics and easy-to-read drawings on identifying and fixing problems. The PLC and associated sensors can be set up with tolerance bands so you can build in predictive maintenance into your machine with unacceptable variations in load; temperatures; vibration; torque; belt tightness; gear meshing etc detected and reported via the HMI.
Thanks to Dan Throne off Rexroth Bosch Group for a great whitepaper (and no, we don’t get paid for promoting them!). I think I can safely say with my experiences with troubleshooting mechatronics systems that this comment is probably true from Sidney J. Harris: Never take the advice of someone who has not had your kind of trouble.
Yours in engineering learning
Steve
