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Using an electronic gyroscope with real-time microcontroller; design and implementation of an impedance type kinesthetic interface with high pose, force and timing fidelity

2019
Sızlayan, Seyit Yiğit
In this thesis, we propose the design of a 1-DOF kinaesthetic (kinesthetic) force feedback interface for haptic and other robotic applications. The developed system is based on direct-drive principle. Thus, it provides a mechanically robust (and easy-to-build), and affordable solution. The major advantage of the direct-drive approach is that the coupling between the actuator and human motion is transparent, a desired feature for human-machine interfaces. The main drawback of a direct-drive actuator interface is that the effective motion measurement resolution is very low compared to other systems that utilize capstan-drive-like mechanisms. To overcome this low motion measurement resolution problem, we used an electronic gyroscope to measure the angular velocity from the hand grip transparently. We integrate the asynchronous encoder and synchronous gyroscope measurements to get high fidelity motion information using a statistical fusion filter implemented on an embedded microcontroller board. We developed three different filters, all based on Kalman estimator. Two of the filters fuse the synchronous gyroscope measurements with the asynchronous encoder measurements. One of the two filters uses a classical second-order constant velocity model where the gyroscope and the encoder measurements are treated as observations/measurements. The latter model is a first-order filter where the gyroscope measurements drive the system from the input terminal. The last filter is also a second order filter where we only use the encoder for both position and velocity estimation. We tested and compared the designed filters on encoders with resolution down to 400CPR. Results show that the filters that utilize the gyroscope measurements substantially outperform the encoder-only solution in terms of estimation precision. We did not observe significant differences between the filters that use the gyroscope. The integrated system provides us 1KHz hard-real-time operation and programmable interfaces for a considerably low cost. Another critical sub-system of an haptic interface is the torque control module whose bandwidth needs to be high enough for accurate impedance control. In the literature, PWM based closed-loop torque control is commonly used for this purpose. However, in this thesis, we designed a high-bandwidth, OPAMP-based current controller for rendering force commands. We compared a PWM based solution with our driving circuit and showed that our force control policy provides a much better torque tracking performance. The most important performance metric of a haptic interface is the Z-width of the system, which directly depends on the measurement accuracy, sampling rate, and the force-fidelity. Due to extremely low effective resolution caused by direct-drive mechanisms, the vast majority of the haptic interfaces uses the capstan-like transmission to satisfy the high Z-width requirements. Indeed, our system achieves high measurement and force rendering accuracy, and a quite fast 1KHz hard-real-time operation, while still enjoying the benefits of a direct drive approach. We believe that our approach in this thesis can be used to design and develop direct-drive based (high DOF) haptic systems with great Z-width performance.