Wavelet packet transform based compression for bilateral teleoperation

This paper introduces a codec scheme for compressing the control and feedback signals in bilateral control systems. The method makes use of Wavelet Packet Transform (WPT) and Inverse Wavelet Packet Transform (IWPT) for coding and decoding operations respectively. Data compression is carried out in low pass filter output by reducing the sampling rate; and in high pass filter output by truncating the wavelet coefficients. The proposed codec works on both directions of signal transmission between a master robot and a slave robot over a networked motion control architecture. Following the formulation of the compression/decompression methodology, experimental validation is conducted on a single degree of freedom (DOF) motion control system. In the experiments, responses from different Wavelet structures are analyzed and a comparative study is carried out considering the factors of compression rate, reconstruction power error and real time computational complexity. It is confirmed that the controller using the proposed compression algorithm performs very close to the uncompressed one while enabling transmission of much less data over network

Application of Ethernet Powerlink for communication in a Linux RTAI open CNC control system

In computerized numerical control (CNC) systems, the communication bus between the controller and axis servo drives must offer high bandwidth, noise immunity, and time determinism. More and more CNC systems use real-time Ethernet protocols such as Ethernet Powerlink (EPL). Many modern controllers are closed costly hardware-based solutions. In this paper, the implementation of EPL communication bus in a PC-based CNC system is presented. The CNC system includes a PC, a software CNC controller running under Linux Real-Time Application Interface real-time operating system and servo drives communicating via EPL. The EPL stack was implemented as a real-time kernel module. Due to software-only implementation, this system is a cost-effective solution for a broad range of applications in machine control. All software systems are based on GNU General Public License or Berkeley Software Distribution licenses. Necessary modifications to the EPL stack, Linux configurations, computer basic input/output system, and motherboard configurations were presented. Experimental results of EPL communication cycle jitter on three different PCs were presented. The results confirm good performance of the presented system

Assistive control for non-contact machining of random shaped contours

Recent achievements in robotics and automation technology has opened the door towards different machining methodologies based on material removal. Considering the non force feedback nature of non-contact machining methods, careful attention on motion control design is a primary requirement for successful achievement of precise cutting both in machining and in surgery processes. This thesis is concerned with the design of pre-processing methods and motion control techniques to provide both automated and human-assistive non-contact machining of random and complex shaped contours. In that sense, the first part of the thesis focuses on extraction of contours and generation of reference trajectories or constraints for the machining system. Based on generated trajectories, two different control schemes are utilized for high precision automated machining. In the first scheme, preview control is adopted for enhancing the tracking performance. In the second scheme, control action is generated based on direct computation of contouring error in the operational space by introducing a new coordinate frame moving with the reference contour. Further, non-contact machining is extended for realization in a master/slave telerobotic framework to enable manual remote cutting by a human operator. With the proposed approach, the human operator (i.e. a surgeon) is limited to conduct motion within a desired virtual constraint and is equipped with the ability of adjusting the cutting depth over a that contour providing advantage for laser surgery applications. The proposed framework is experimentally tested and results of the experiments prove the applicability of proposed motion control schemes and show the validity of contributions made in the context of thesis