Experimental comparison between proportional and PWM-solenoid valves controlled servopneumatic positioning systems

The performance of the Dynamical Adaptive Backstepping-Sliding Mode Control (DAB-SMC) scheme for positioning of a pneumatic cylinder regulated by two types of PWM-solenoid valves is experimentally investigated. The goal is to study the compromise in controller’s performance as the system moves from using a proportional valve to employing the low-cost PWM-solenoid valves. Sinusoidal and multiple-step inputs are used as the reference position trajectories. Experimental results show that the DAB-SMC scheme works best with the proportional valve. The performance, however, deteriorates by more than twofold, once the system utilizes PWM- solenoid valves of 3/2-way or 2/2-way configurations. From this study, tradeoff between performances of different types of valves applied on a DAB-SMC scheme-controlled servo positioning system is successfully documented. This information helps to configure appropriate servopneumatic system for positioning applications

Position referenced force augmentation in teleoperated hydraulic manipulators operating under delayed and lossy networks: a pilot study.

Position error between motions of the master and slave end-effectors is inevitable as it originates from hard-to-avoid imperfections in controller design and model uncertainty. Moreover, when a slave manipulator is controlled through a delayed and lossy communication channel, the error between the desired motion originating from the master device and the actual movement of the slave manipulator end-effector is further exacerbated. This paper introduces a force feedback scheme to alleviate this problem by simply guiding the operator to slow down the haptic device motion and, in turn, allows the slave manipulator to follow the desired trajectory closely. Using this scheme, the master haptic device generates a force, which is proportional to the position error at the slave end-effector, and opposite to the operator's intended motion at the master site. Indeed, this force is a signal or cue to the operator for reducing the hand speed when position error, due to delayed and lossy network, appears at the slave site. Effectiveness of the proposed scheme is validated by performing experiments on a hydraulic telemanipulator setup developed for performing live-line maintenance. Experiments are conducted when the system operates under both dedicated and wireless networks. Results show that the scheme performs well in reducing the position error between the haptic device and the slave end-effector. Specifically, by utilizing the proposed force, the mean position error, for the case presented here, reduces by at least 92% as compared to the condition without the proposed force augmentation scheme. The scheme is easy to implement, as the only required on-line measurement is the angular displacement of the slave manipulator joints

Selection of network parameters in wireless control of bilateral teleoperated manipulators.

This paper describes how to establish performance charts for selection of network parameters for effective utilization of a bilateral teleoperated manipulator working under a wireless communication channel. The goal is to construct a set of charts that help researchers and engineers to select appropriate parameters of wireless network setup for a known configuration of environment obstruction. To achieve this goal, a teleoperated setup comprising a master haptic device, a slave manipulator dynamic simulator, and a communication channel emulated using the network simulator version 2 (NS2) simulator is first developed. Next, performance indices are defined to evaluate the quality of position tracking of the slave manipulator end-effector and force tracking of the master haptic. Three indices chosen in this paper are the integral of squared position and force errors, the integral of absolute position and force error, and the amplitude of position and force overshoot. Extensive experiments on the developed setup are then conducted to study effects of time-varying packet loss on the performance of the teleoperated system. The largest mean packet loss, at which the system exhibits satisfactory tracking, is then quantified. This packet loss is used as an indicator to define regions representing the quality of tracking. The effectiveness of the proposed technique is validated by testing a fully instrumented hydraulically actuated system under various real wireless channel scenarios

A prototype telerobotic platform for live transmission line maintenance: review of design and development.

This paper reports technical design of a novel experimental test facility, using haptic-enabled teleoperation of robotic manipulators, for live transmission line maintenance. The goal is to study and develop appropriate techniques in repair overhead power transmission lines by allowing linemen to wirelessly guide a remote manipulator, installed on a crane bucket, to execute dexterous maintenance tasks, such as twisting a tie wire around a cable. Challenges and solutions for developing such a system are outlined. The test facility consists of a PHANToM Desktop haptic device (master site), an industrial hydraulic manipulator (slave site) mounted atop a Stewart platform, and a wireless communication channel connecting the master and slave sites. The teleoperated system is tested under different force feedback schemes, while the base is excited and the communication channel is delayed and/or lossy to emulate realistic network behaviors. The force feedback schemes are: virtual fixture, augmentation force and augmented virtual fixture. Performance of each scheme is evaluated under three measures: task completion time, number of failed trials and displacement of the slave manipulator end-effector. The developed test rig has been shown to be successful in performing haptic-enabled teleoperation for live-line maintenance in a laboratory setting. The authors aim at establishing a benchmark test facility for objective evaluation of ideas and concepts in the teleoperation of live-line maintenance tasks

On quantitative feedback design for robust position control of hydraulic actuators

The article of record as published may be located at http://dx.doi.org/10.1016/j.conengprac.2009.11.007This paper discusses several practical issues related to the design of robust position controllers for hydraulic actuators by quantitative feedback theory (QFT). Important properties of the hydraulic actuator behavior, for control system design, are identified by calculating a family of equivalent frequency responses from acceptable nonlinear input-output data. The role of this modeling approach towards reducing over-design by decreasing the sizes of the QFT plant templates is described. The relationship between the geometry of the QFT bounds and the complexity of the robust feedback law is examined through the development of two low-order controllers having characteristics suitable for different applications. Experimental test results demonstrate the extent that each QFT controller is able to maintain robustness against variations in the hydraulic system dynamics that occur due to changing load conditions as well as uncertainties in the hydraulic supply pressure, valve spool gain, and actuator damping.The authors thank the Natural Sciences and Engineering Research Council of Canada (NSERC) who provided financial support for this research

Dynamic simulation and control of teleoperated heavy-duty hydraulic manipulators

Some relevant aspects of dynamics and control of heavy-duty hydraulic machines in a teleoperated mode were investigated. These machines, such as excavators and forest harvesters, are mostly used in primary industries. They have a manipulator-like structure with a nonlinear and coupled actuating system. The aim of the project is to investigate different approaches towards converting such machines, with minimum changes, into task-oriented human-supervisory control systems. This provides the opportunity to use both human supervision and robotic power in hazardous environments and for tasks for which human decision is necessary. A methodology was developed for fast and accurate simulations. Analytical, steady-state and numerical techniques were combined using Large-Scale Systems analysis. The inclusion of nonlinearities in the form of discontinuities (e.g., gear backlash and stick-slip friction) in the model was investigated. Numerical simplifications of the structural dynamics and alternative solutions for the hydraulic part were also studied. The model describing the performance of the machine has been written in ACSL (Advanced Continuous Simulation Language) on a VAX computer system. A modified version of the program is at present running close to real-time on a single processor in conjunction with high speed graphics in a manner similar to a flight simulator used for human interface studies and training. The model also evaluates the performance of the machine in a teleoperated mode and under different control strategies. As a result a velocity control algorithm has been developed which is applied in conjunction with the closed-loop components for teleoperation of heavy-duty hydraulic machines; it is basically a feedforward compensation which uses the measured hydraulic line pressures along with fluid-flow equations as criteria to control the joint velocities as well as to uncouple the interconnected actuating system. The control algorithm has been written in C language and is running on an IRONICS computer system, interfaced between the human operator and the machine. The simulation results are supported by the experimental evidence. The experiments were performed on a Caterpillar 215B excavator. Improved operator safety, extension of human capability, job quality and productivity increase are the advantages of a successful implementation of robotic technology to these industrial machines.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

Computer-aided rolling of parts with variable rectangular cross-section

A computer-aided process planning scheme for flat rolling of symmetric parts with variable rectangular cross-section is proposed. As a starting point, El-Kalay and Sparling's formula for spread was found to be suitable for this application and thus was used in developing the method. Two distinct criteria were considered in the analysis, namely: kinematic and dynamic constraints. In order to control the precision of the rolled parts, provisions were made for specifying the tolerances of the finishing passes in the form of convexity constraints. Numerical formulation was used and the resulting non-linear equations were solved by an iterative method. Based on the process constraints and the numerical solution, a computer algorithm was then developed to determine the number of rolling passes required, as well as the dynamic variation of the roll gap as a function of the rolled length. Preliminary laboratory experiments were then conducted to verify the validity of the predicted results and the applicability of the spread formula in determining the process behaviour. These experiments led to the modification of the spread formula. Using the modified formula it was found that a good agreement existed between the predicted results and those of the experiments. Operating aspects were also considered. It was proposed that a control system based on the rolled length would be both simple and suitable. It was then concluded that for rectangular parts with moderate variation in shape and reasonable complexity, where formed-die rolling and die-forging are also applicable, this method has considerable advantages as it replaces the forging hardware with the rolling software.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

Interpolation of Bandlimited Signals from Uniform or Non-uniform Integral Samples

A digital filter with finite impulse response is developed for interpolating a bandlimited signal at an arbitrary point from uniform or non-uniform integral samples. The convergence of approximation is established via a closed form upper bound on the error of interpolation. The accuracy of interpolation is further demonstrated with numerical experiments. The proposed method has potential applications in the design of interferometers and integrating sensors

Comparison Between an Intelligent Controller and a Sliding Mode Controller to Positioning Pneumatic Actuators

Sliding Mode Control (SMC) technique is a well-established method in positioning pneumatic actuators due to its consistent performance in the presence of model uncertainties. Brain Emotional Learning Based Intelligent Controller (BELBIC) is a new model free controller with flexible structure and low computational load. It has been successfully applied to many control problems. In this work we study, for the first time, how well a BELBIC performs in comparison with SMC approach in positioning a pneumatic actuator. Different position tracking tasks are evaluated on a low-cost pneumatic actuator and in presence of significant friction. Comparison is done based on positioning accuracy, non-oscillatory motion and robustness to external load. The results show that while both controllers successfully track different trajectories, SMC is generally more accurate. BELBIC maintains its performance in the presence of large static friction. Furthermore, it produces less oscillatory control action. This work concludes that BELBIC can be a good choice for positioning of pneumatic actuators. 1