Blue Joule Corporation answered the call from Johns Hopkins University - Applied Physics Laboratory (JHU-APL) for a compact gimbal for use as laboratory equipment to allow for extremely precise testing and documenting of their own equipment. The company developed and recently delivered the Mini Mount (MM) Gimbal. Made of stainless steel and comprised of a package of pre-integrated motion control components from various HEIDENHAIN brands, the gimbal is approximately 20" tall and is tested to be accurate at better/smaller than 1/1000th of a degree.
“This is in the top tier in the world of gimbals and designed at lower costs than previously attainable,” explained Neal Romine, owner of Blue Joule Corp. Over the past 40 years, Romine has worked for such companies as McDonnell Douglas Aircraft and Emerson Electric and served as past owner of Multiple Services Technologies before its 2004 sale to EMS Technologies.
Romine added that although the gimbal is on the smaller scale in stature, the accuracy level of the positioning gimbal is what is typically used in equipment that tracks aircraft. “In the past, I fulfilled a contract with NASA for a gimbal used for tracking of the space shuttle’s return to flight (RTF) program, so I know,” said Romine. “I call this new gimbal for JHU-APL the Mini Mount because it’s about half the size of a typical gimbal of these types.”
“The requirement of this gimbal project for Johns Hopkins University was for an extremely high-precision positioning system/platform in order to be able to provide highly accurate position feedback,” said Romine. “It will likely first be mounted with some sort of optical stabilization equipment for very high-speed photography, though the options of course are theirs. Therefore, the selection of the use of the highly accurate AMO absolute encoders (made of a multi-layered stainless-steel ring) that integrated seamlessly with the motors and controller were a critical part of its design.”
The development of the Blue Joule MM gimbal took more than a year to complete and provides ±4 arcsec level accuracy, with sub-arcsecond repeatability and 23 bits of resolution. Part of the unique design includes the use of two encoder reader heads that combine with one encoder ring, which then eliminates mechanical errors and thus boosts the accuracy levels. “This gimbal provides 23 bits of resolution at an unusually low cost and is extremely rugged. You can spray it down with dirty oil and it just doesn’t care,” said Romine.
The AMO angle encoder used is the combined flange-mounted WMFA ring and two WMKA absolute reader heads that seamlessly communicate with the system using the EnDat 2.2 interface to connect with ETEL TMB+ motors and AccurET 300 drive control. “While other interface options are available, this entire package was chosen because it was made up of all HEIDENHAIN brand components, which offered a big risk reduction in implementation,” added Romine. “That’s not available anywhere else and afforded me the luxury of avoiding a lot of debugging that I just didn’t have to do. It’s an extremely high-accuracy and reliable positioning system.”
The structure of any gimbal is comprised of three main sections: a Riser assembly, an Elevation section, and an Azimuth assembly. The MM is a two-axis (elevation over azimuth) gimbal with each axis powered by an ETEL TMB+ motor. These frameless torque motors are capable of up to 66.1 Nm of torque. “This motor was chosen because of its excellent quality and integrated cooling that offers just another level of reliability to the MM gimbal,” said Romine.
The MM has operational travel range of ±155 degrees in Azimuth and ±95 degrees in Elevation. These travel limits simplify the mechanical system (increasing its reliability) and include elastomer bumpers.
Romine emphasized the fact that the MM structure is made of stainless steel that is inherently corrosion-resistant and incredibly stiff, making this gimbal extremely unique. “In my 40 years in business, I have never seen a gimbal manufactured of stainless steel,” said Romine.
He added that aluminum is the usual material used for gimbal development because it is traditionally available at a lower cost, is easier to machine, and has good thermal transfer. Since stainless steel has come down in price recently, Blue Joule was able to very closely match thermal characteristics between the bearings and the housings. This is typically a problem that requires a complex manufacturing process. Also, stainless steel is known to be significantly better in terms of durability, payload capacity, and performance (stiffness). “Stiffness is paramount in a gimbal,” said Romine. “If you want to hang a heavy payload like a camera or telescope off it, you want to minimize the flexure and make sure that nothing droops. And while it is heavier than aluminum, this was not a concern for JHU-APL.”
As usual protocol, a host of tests are completed on all new Blue Joule project designs. One example of testing on the MM include Simple Step and Ramp. Here, Simple Step and Ramp responses of the system showed exceptional performance. The autotuning feature of the ETEL AccurET/ComET controller software allowed quick, critically damped tuning. It also allows for intuitive manual tuning for those so inclined. “The auto-tuning in Elevation worked so well it almost looks too good,” said Romine.
This new gimbal will allow JHU-APL to mount larger, heavier payloads in a smaller footprint while operating with higher precision than traditionally available. “Especially for a gimbal of this size and price, the accuracy is exceptional,” shared Romine. “And while very few organizations have needed this level of accuracy (such as big telescopes do), that is changing. Possible upcoming applications for something like this include tracking and surveillance systems, stabilized platforms, and high-level camera mounts, to name a few.”
This article was contributed by HEIDENHAIN, Schaumburg, IL. For more information, visit here .