Dr. Daniel Opila

Haptic Interface Design for an Embedded Controls Class

This was my first project the summer I came to Michigan. The electrical engineering (EE) department runs a lab-based embedded control class (EE 461). Students learn to program the MPC-555, a fairly powerful embedded processor for real-time applications that is popular in automotive applications. The student body is a mix of junior and senior undergraduates with first and second year graduate students, mostly from the EE department. As part of this class, students learn to interface with mechanical components, specifically a motor-driven hand wheel that serves as a haptic interface. They simulate virtual springs, dampers, walls, etc. Later in the semester they use it as driving simulator with assisted lane-holding, where the wheel exerts a small force to help keep you in your lane.
A lab station
Driving with steering assist.

The existing interface device was used for several years, but had some reliability issues with the housing, bearings, and a chain drive. The course instructors wanted a replacement that was more reliable and had better performance. The realism of a haptic simulation (the "feel") is highly dependent on the mechanical device characteristics, so the new device needed to be precise, repeatable, and have good frequency response characteristics.

A lab station
The haptic wheel. Note the red
emergency stop on the side.

The site shows pictures of the old and new designs, CAD designs, mechanical drawings, specifications, and parts lists. This system was designed to be quite versatile and could be used for haptic research as well. The connectors are standardized and the device has 5V and +/- 12V power on board that can be used to power external interface electronics. Optical isolation and careful grounding schemes allow the user several grounding/interface options without modifying the device. An optional force sensor is included; the motor typically mounts on a solid aluminum plate that can be replaced with a machined force sensor. The force sensor can be manually or automatically machined from a flat plate. Only one side is machined, so no refixturing or repositioning is required. Strain gages are attached at appropriate places. The design was a compromise between sensitivity, durability, maximum loads, and modal frequencies.

Power box
The power box sits under the desk.

Inside the power box
Inside the power box: 400W/24V power supply (silver), current amplifier (black),
and inductors (red).

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