Yaser Maddahi

Calibration of wheeled mobile robots with differential drive mechanisms: An experimental approach

Exact knowledge of the position and proper calibration of robots that move by wheels form an important foundation in mobile robot applications. In this context, a variety of sensory systems and techniques have been developed for accurate positioning of differential drive mobile robots. This paper, first, provides a brief overview of mobile robots positioning techniques and then, presents a new benchmark method capable of calibrating mobile robots with differential drive mechanisms to correct systematic errors. The proposed method is compared with the commonly used University of Michigan Benchmark (UMBmark) odometry method. Two sets of comparisons are conducted on six prototyped robots with differential drives. The first set of tests establishes the workability and accuracy that can be achieved with the new method and compares them with the ones obtained from the UMBmark technique. The second experiment compares the performance of a mobile robot, calibrated with either the UMBmark or the new method, for an unseen path. It is demonstrated that the proposed method of calibration is simple to implement, and leads to accuracy comparable to the UMBmark method. Specifically, while the error corrections in both methods are within i¾±5% of each other, the proposed method requires single straight line motion for calibration, which is believed to be simpler and less timely to implement than the square path motion required by the UMBmark technique. The method should therefore be considered seriously as a new tool when calibrating differential drive mobile robots.

An augmented virtual fixture to improve task performance in robot-assisted live-line maintenance

Display Omitted We introduce the concept of augmented virtual fixtures to reduce tracking error.We experimentally validate effectiveness of the proposed scheme.The application, targeted in this paper, is live transmission line maintenance.The proposed scheme shows a marked improvement over the virtual fixture mode alone.Specifically, for presented experiments, our scheme reduces position error by 71%. Virtual fixtures can be used in haptic-enabled hydraulic telemanipulators to facilitate certain tasks. Using this concept, however, the operator may tend to move the master fast due to relying on the virtual fixture. As a result, the slave manipulator could start to lag due to latency in the hydraulic actuation control system. This paper describes how to mitigate the position errors between master and slave robots by overlaying an augmentation force on the master that is collinear but opposite of the master instantaneous velocity. The magnitude of this force is proportional to the position error at the slave end-effector. Experiments, conducted on a teleoperated hydraulic manipulator to perform several live-line maintenance tasks, show that the augmented scheme exhibits less position error at the slave side, better task quality, but longer task completion time as compared to the virtual fixture alone.

Live-line maintenance training using robotics technology

This paper describes performance evaluation of a teleoperated platform which allows operators to remotely perform live-line maintenance. Effectiveness of the system is validated when several maintenance tasks are performed by novice (students) and experienced (linemen) operators. The system comprises a PHANToM Desktop haptic device controlling a Kodiak hydraulic manipulator. Validations are performed under two modes, when the operators are asked to guide the slave manipulator by moving the haptic device implement. In the first mode, the force capability of the haptic device is not utilized. In the second mode, the haptic device is used to create a forbidden region virtual fixture that helps the operator stay on the desired path. In the second mode, the task completion time reduces as compared to the mode in which no force is generated by the haptic. The concept of virtual fixture also results in a smooth motion at the slave manipulator end-effector, and reduces the mental load on both expert and novice operators. Furthermore, the system familiarizes the participants with new techniques used in live-line maintenance in a controlled experimental setting.

WIRELESS CONTROL OF A TELEOPERATED HYDRAULIC MANIPULATOR WITH APPLICATION TOWARDS LIVE-LINE MAINTENANCE

This paper presents the procedure of establishing performance charts for effective utilization of a teleoperated hydraulic manipulator working under wireless communication channels. A teleoperated system, comprising a master haptic device and an industrial hydraulic manipulator, is constructed. The master and slave communicate through a communication channel emulated using the NS2 simulator. Two sets of experiments are designed to construct performance charts that guide us to select appropriate parameters of wireless network setup by which a particular value of position error appears at the slave hydraulic manipulator end-effector. The network parameters are: configuration of environment obstruction, transmission power of the router, and distance between the master and slave sites. The first set of experiments is conducted to define three regions of tracking quality, and to construct the performance charts. The second set of experiments confirms satisfactory performance, when the teleoperated system is located within the recommended regions in the established charts. One application of this study is live-line maintenance using remotely-operated hydraulic manipulators.

Haptic-enabled teleoperation of base-excited hydraulic manipulators applied to live-line maintenance

This paper investigates haptic-enabled teleoperation of a base-excited hydraulic manipulator working under a wireless communication channel. The intended application is live power line maintenance. With respect to this application, three main challenges are recognized in the field: need for the force feedback, wireless communication between master and slave sites, and base excitation of the slave manipulator. In this paper, a test rig is developed to examine how an operators hand speed regulating scheme enhances the linemans performance while the entire system works under a wireless communication channel and the slave base is under excitation. Two sets of experiments are performed when the haptic device produces no force and when the regulating haptic force is added to the master device. Performance of the system is evaluated by measuring four indices: operators failure in completing a task, end-effector displacement, slave manipulator controller effort, and task completion time. Results indicate that adding the haptic force to the system helps linemen function more effectively when the system is subject to base-excitation and communicates through a wireless network.

Position referenced force augmentation in teleoperated hydraulic manipulators operating under delayed and lossy networks

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 operators 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. We introduce a novel force scheme for master-slave setups operating under a delayed/lossy network.The scheme reduces position errors at the slave end-effector, caused by the delay and packet loss.We experimentally validate effectiveness of the scheme by testing on a teleoperated hydraulic manipulator.Addition of the proposed scheme, for the cases tested, could reduce tracking errors up to 92%.We detect significant difference between slave position errors with and without the force scheme.

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.

Calibration of omnidirectional wheeled mobile robots: method and experiments

Odometry errors, which occur during wheeled mobile robot movement, are inevitable as they originate from hard-to-avoid imperfections such as unequal wheels diameters, joints misalignment, backlash, slippage in encoder pulses, and much more. This paper extends the method, developed previously by the authors for calibration of differential mobile robots, to reduce positioning errors for the class of mobile robots having omnidirectional wheels. The method is built upon the easy to construct kinematic formulation of omnidirectional wheels, and is capable of compensating both systematic and non-systematic errors. The effectiveness of the method is experimentally investigated on a prototype three-wheeled omnidirectional mobile robot. The validations include tracking unseen trajectories, self-rotation, as well as travelling over surface irregularities. Results show that the method is very effective in improving position errors by at least 68%. Since the method is simple to implement and has no assumption on the sources of errors, it should be considered seriously as a tool for calibrating omnidirectional mobile having any number of wheels.

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.

Development of a graphical user interface for a socially interactive robot: A case study evaluation

In this paper, we present the development of a graphical user interface for a commercially available humanoid robot to study its interaction with children. The interface has been designed to facilitate the overall operation of the robot, and ultimately improve the interaction with children. Four pilot cases are studied to investigate overall effectiveness of the developed robotic setup in interacting and educating children. Case studies included communication with children in university environment, a day nursery, a junior high school, and at the Winnipeg Childrens Hospital. Children and their parents/staffs were asked to provide feedback on how they/their children felt about interacting with the robot. Responses were then translated into quantitative measures. The measures received by each group of children and parents/staffs were compared using the ANOVA test. Results failed to reject the null hypothesis of equality in means of all measures. Therefore, the feedback, provided by both groups using questionnaires, was considered very close to each other. In other words, results indicated that children and parents/staffs expressed great interest in use of the developed system, and believed that such a robot could be a helpful tool in child therapy like autism.