Overcoming limitations, compact DC servo design delivers torque and precision for battery-powered robots
BY TOM HOFFMAN, PRESIDENT/CEO, R.M. HOFFMAN COMPANY
A picture is worth a thousand words. But a video is worth millions. The following news video from CNET shows an example of remarkably efficient warehouse robots in action. Each battery-driven robot transports portable industrial shelving from vast warehouse storage to the stock-picking area. One of the most efficient warehousing and fulfillment schemes ever devised by humans, this example demonstrates rechargeable robots operating 24/7. Durability and reliability are key qualities for the underlying hardware. These same qualities are found in the robotic drive designed by Hoffman for our comparable application.
Tight Space, DC Power and Short Deadline Dictated Creative Engineering
- 24VDC battery-powered operation with an emphasis on power conservation
- Sufficient torque to precisely rotate the robot via a turntable as it supports a huge stack of multi-tiered industrial shelving loaded with several hundred pounds of products
- The design envelope was exceptionally small, a low profile space too challenging for our client
- Special gearing, connectors and adapters were needed to meet specifications. For example, connector positions were tightly specified with no margin for error
Working against a short deadline, our design team employed standard and non-standard components to fashion the solution. The DC servo at the heart of the drive and several other components were special challenges due to a lack of off-the-shelf solutions. Project engineer Ray Krieger recalls
"the robot’s turntable motion and restrictive physical envelope were fully defined and could not be changed. And the electrical connector position was extremely restricted. We had to figure out how to provide the motion in the confined space while guaranteeing the exact connector position."
- We created a planetary gear train containing a tapered roller bearing; and engineered an available planetary section (a partial gearbox).
- Thanks to great contacts and relationships, our DC motor vendor was willing to custom-make a special, short sealed motor at a competitive cost. This motor delivered speed, torque and low heat within tough limits while being very compact.
- The motor design included a wiring exit to match the electrical connector position which happened to be at an angle with respect to the motor centerline (very difficult considering the manufacturer’s normal layout of internal wiring).
- A taper roller bearing was needed to absorb the thrust and radial loads of the application. We worked with our gearbox vendor to supply a cross key female attachment to handle the reversing torque of the drive, all at a competitive cost.
- We designed a spur gear output with cross key attachment, choosing an appropriate vendor to supply.
- We found and added the required compatible shaft encoder to custom fit the confined envelope and mate with the customer’s digital control system.
In future blog episodes, we’ll present other interesting case studies of Hoffman’s value-added motion solutions developed to solve specific problems. In the meantime, please review our wide range of successful projects. You’ll be able to get in touch quickly to begin our Discovery process with no obligation. CLICK HERE.