T.M. Lam

Artificial Force Field for Haptic Feedback in UAV Teleoperation

The feedback upon which operators in teleoperation tasks base their control actions differs substantially from the feedback to the driver of a vehicle. On the one hand, there is often a lack of sensory information; on the other hand, there is additional status information presented via the visual channel. Haptic feedback could be used to unload the visual channel and to compensate for the lack of feedback in other modalities. For collision avoidance, haptic feedback could provide repulsive forces via the control inceptor. Haptic feedback allows operators to interpret the repulsive forces as impedance to their control deflections when a potential for collision exists. Haptic information can be generated from an artificial force field (AFF) that maps environment constraints to repulsive forces. This paper describes the design and theoretical evaluation of a novel AFF, i.e., the parametric risk field, for teleoperation of an uninhabited aerial vehicle (UAV). The field allows adjustments of the size, shape, and force gradient by means of parameter settings, which determine the sensitivity of the field. Computer simulations were conducted to evaluate the effectiveness of the field for collision avoidance for various parameter settings. Results indicate that the novel AFF more effectively performs the collision avoidance function than potential fields known from literature. Because of its smaller size, the field yields lower repulsive forces, results in less force cancellation effects, and allows for larger UAV velocities. This indicates less operator control demand and more effective UAV operations, both expected to lead to lower operator workload, while, at the same time, increasing safety.

Collision avoidance for a remotely-operated helicopter using haptic feedback

This paper introduces four new collision avoidance systems for a remotely-operated helicopter using haptic feedback on the control stick of the operator. To calculate the feedback force artificial risk fields are used, which give an indication about the risk of hitting an obstacle. For each obstacle in the risk field a risk value is calculated, which is transformed to a risk vector, acting as an artificial force on the vehicle. All risk vectors are integrated into one avoidance vector, which is proportional to the feedback force to the operator. A basic risk field and a parameterized risk field are tested in simulations, together with two risk vector calculation methods, resulting in radial and normal risk vectors. The simulations show most promising results for the parameterized risk field with radial risk vectors and worst results for the basic risk field with normal vectors

Haptic Feedback for UAV Tele-operation - Force offset and spring load modification

Haptic feedback is often suggested to complement visual information through the sense of touch to improve efficiency and safety in the tele-operation of unmanned aerial vehicles. It is, however, of great importance that the improvements are not at the cost of higher operator workload and control activity, which strongly depends on how haptic feedback is presented to the operator. This paper describes the study on two different techniques of haptic feedback for collision avoidance in the tele-operation of a UAV helicopter. The first technique considers the addition of an external force offset generated by an artificial force field, whereas the second technique considers the addition of an external spring constant. The study involves a theoretical analysis and an experimental evaluation of the two haptic feedback implementations. Experiment results indicate that the use of the external spring constant outperforms the force offset. Operator performance improves and workload decreases with equivalent control activity and level of safety with respect to the use of force offset.

Haptic Feedback in Uninhabited Aerial Vehicle Teleoperation with Time Delay

In the teleoperation of an uninhabited aerial vehicle, haptic feedback can be used to provide useful information through the sense of touch. Although this can improve performance and enhance situation awareness, time delays caused by signal transmission generally induce control problems with haptic feedback, causing unsafe operations. Wave variables have been suggested to cope with the control problems in bilateral human-machine systems with time delay. Very little has been reported, however, on effects related to human control activity and workload when using wave variables. This paper describes a theoretical analysis of using wave variables to enhance a collision-avoidance system for visual and haptic uninhabited aerial vehicle teleoperation with time delay. An experiment was conducted to evaluate its effectiveness regarding operator performance, control activity, workload, and the safety of operation. Results indicate that wave variables are indeed successful in improving human performance. The number of collisions, operator control activity, and workload all decreased. Whereas performance and control activity were equivalent to the situation of haptic feedback without time delay, workload remained higher.

Effect of haptic feedback in a trajectory following task with an unmanned aerial vehicle

Due to the limited field of view of a camera, visual information may not be sufficient to control an unmanned aerial vehicle (UAV). In particular when the camera is not pointing into the direction of motion, perception of environment constraints can be considerably difficult. The use of haptic feedback would provide tactile cues complementing the information from the visual channel. This paper presents the results of an experimental evaluation of using haptic feedback for manual control of an UAV helicopter in a trajectory following task. The experiment involves controlling an UAV helicopter along a reference trajectory as fast and accurately as possible. The trajectory is represented by a three-dimensional tunnel-in-the-sky display of which the walls represent the environment constraints. The experiment only considers the horizontal plane. The results of the experiment indicate that haptic feedback can be used to support the operator in perceiving tunnel walls as environment constraints. The performance, control activity and workload strongly depend on the manner in which repulsive forces are fed back to the human operator.

Collision avoidance in UAV tele-operation with time delay

Tele-operation of an unmanned aerial vehicle (UAV) may involve time delay due to signal transmission. This will result in poor operator performance and control difficulties. Particularly, in a tele-operation system with haptic feedback, time delay may lead to instability, which leads to unsafe tele-operation. Wave variables are often suggested as a method for increasing operator performance in a bilateral system with time delay. However, very little has been reported about effects on human-machine interactions, such as control activity and workload, when using wave variables. This paper describes a theoretical analysis of using wave variables with a collision avoidance system for UAV tele-operation with time delay. An experiment was conducted to evaluate the effectiveness of wave variables in a collision avoidance system for tele-operation with time delay in a UAV control station equipped with haptic feedback. Operator performance, safety, control activity, and workload were studied. Results indicate that wave variables can increase the performance of a collision avoidance system with presence of time delay. The amount of collisions, control activity, and workload decreased. Operator performance remained the same as with no time delay.

Comparison of Control and Display Augmentation for Perspective Flight-Path Displays

Manually performed piloting tasks with a perspective flight-path display require considerable effort. To improve this, display augmentation is used: additional symbology such as a flight-path predictor is added. An alternative approach would be to use control augmentation, using fly-by-wire techniques to simplify the control task of the pilot. A control-theoretical analysis of different display and control augmentation concepts is presented. It is shown how design techniques for flight directors can be applied to the analysis of display augmentation. The different concepts have also been tested in a piloted experiment, conducted in a high-fidelity moving-base flight simulator. Experimental results confirm the findings from the control-theoretical analysis. Overall, the control augmentation concepts outperform the display augmentation concepts: Pilot workload and control activity are strongly reduced with equal or better performance. These benefits become more apparent as the task difficulty increases.

Force-Stiffness Feedback in Uninhabited Aerial Vehicle Teleoperation with Time Delay

This study investigates the use of haptic feedback to support the teleoperation of an uninhabited aerial vehicle with time delay. Two means of supplying the haptic feedback are investigated: first, an additional force on the control inceptor, and second, an additional force combined with an increased stiffness of the control inceptor. The advantage of combining the force feedback with stiffness feedback, over force feedback alone, is that the additional stiffness of the control inceptor increases the authority of the haptic feedback system in critical situations. The goal of this study is to increase the safety of teleoperation while reducing operator workload. A theoretical analysis shows that force― stiffness feedback improves the stability in the human control loop while allowing for lower force-feedback gain settings as compared with force feedback alone, which indicates that this could contribute to reducing operator workload. In an experiment, the two haptic feedback conditions were compared with a baseline condition without haptic feedback. The fidelity of the experiment was improved over an earlier experiment by introducing a time penalty for collisions. The number of collisions was different for all three conditions, with the lowest number for the force―stiffness condition and the highest number for the baseline condition. Both haptic feedback conditions were rated equally on subjective workload metrics and scored better than the baseline. This finding is in contrast with results from earlier experiments, which indicated a higher workload with haptic feedback, and shows the importance of creating realistic test conditions when using subjective workload ratings.

UAV Tele-operation using Haptics with a Degraded Visual Interface

In the tele-operation of a UAV, haptic feedback can be used to complement visual feedback, resulting in a multi-sensory interface that allows operators to enhance their situation awareness. However, when inconsistencies between haptic information and visual information exist, it is questionable whether haptic feedback is still useful. This paper describes an experimental evaluation of using haptic feedback with a degraded visual interface. The display failure was expressed by errors in the coordinates of objects projected on the navigation display. Experiment results indicate that errors in the navigation display leads to a considerable increase of collisions. Haptic feedback helps reducing the increase of the number of collisions, hence, less deterioration of the level of safety.

Tele-operating a UAV using haptics - modeling the neuromuscular system

This paper describes a theoretical study on the use of an artificial force field in a collision avoidance system to generate force feedback to a neuromuscular arm. The study involves two separate tasks. The first task identifies the intrinsic and reflexive parameters of the human neuromuscular arm model. The second task is to include the neuromuscular arm model in closed-loop offline simulations in order to achieve more insight into the human-machine interaction, when applying haptic feedback. Results indicate that the human neuromuscular arm model responds well to the force feedback generated by the artificial force field and offers the possibility to tune the force field in order to achieve good performance without excessive control activity.