David A. Abbink

Haptic shared control: smoothly shifting control authority?

Literature points to persistent issues in human-automation interaction, which are caused either when the human does not understand the automation or when the automation does not understand the human. Design guidelines for human-automation interaction aim to avoid such issues and commonly agree that the human should have continuous interaction and communication with the automation system and its authority level and should retain final authority. This paper argues that haptic shared control is a promising approach to meet the commonly voiced design guidelines for human-automation interaction, especially for automotive applications. The goal of the paper is to provide evidence for this statement, by discussing several realizations of haptic shared control found in literature. We show that literature provides ample experimental evidence that haptic shared control can lead to short-term performance benefits (e.g., faster and more accurate vehicle control; lower levels of control effort; reduced demand for visual attention). We conclude that although the continuous intuitive physical interaction inherent in haptic shared control is expected to reduce long-term issues with human-automation interaction, little experimental evidence for this is provided. Therefore, future research on haptic shared control should focus more on issues related to long-term use such as trust, overreliance, dependency on the system, and retention of skills.

The effect of haptic guidance on curve negotiation behavior of young, experienced drivers

Haptic feedback on the steering wheel is reported in literature as a promising way to support drivers during steering tasks. Haptic support allows drivers to remain in the direct manual control loop, avoiding known human factors issues with automation. This paper proposes haptic guidance based on the concept of shared control, where both the driver and the support system influence the steering wheel torque. The haptic guidance is developed to continuously generate relatively low forces on the steering wheel, requiring the drivers active steering input to safely negotiate curves. An experiment in a fixed-base driving simulator was conducted, in which 12 young, experienced drivers steered a vehicle - with and without haptic guidance - at a fixed speed along a road with varying curvature. The haptic guidance allowed drivers to slightly but significantly improve safety boundaries in their curve negotiation behavior. Their steering activity was reduced and smoother. The results indicated that continuous haptic guidance is a promising way to support drivers in actively producing (more) optimal steering actions during curve negotiation.

Sharing Control With Haptics: Seamless Driver Support From Manual to Automatic Control

Objective: Haptic shared control was investigated as a human–machine interface that can intuitively share control between drivers and an automatic controller for curve negotiation. Background: As long as automation systems are not fully reliable, a role remains for the driver to be vigilant to the system and the environment to catch any automation errors. The conventional binary switches between supervisory and manual control has many known issues, and haptic shared control is a promising alternative. Method: A total of 42 respondents of varying age and driving experience participated in a driving experiment in a fixed-base simulator, in which curve negotiation behavior during shared control was compared to during manual control, as well as to three haptic tunings of an automatic controller without driver intervention. Results: Under the experimental conditions studied, the main beneficial effect of haptic shared control compared to manual control was that less control activity (16% in steering wheel reversal rate, 15% in standard deviation of steering wheel angle) was needed for realizing an improved safety performance (e.g., 11% in peak lateral error). Full automation removed the need for any human control activity and improved safety performance (e.g., 35% in peak lateral error) but put the human in a supervisory position. Conclusion: Haptic shared control kept the driver in the loop, with enhanced performance at reduced control activity, mitigating the known issues that plague full automation. Application: Haptic support for vehicular control ultimately seeks to intuitively combine human intelligence and creativity with the benefits of automation systems.

Measuring Neuromuscular Control Dynamics During Car Following With Continuous Haptic Feedback

In previous research, a driver support system that uses continuous haptic feedback on the gas pedal to inform drivers of the separation to the lead vehicle was developed. Although haptic feedback has been previously shown to be beneficial, the influence of the underlying biomechanical properties of the driver on the effectiveness of haptic feedback is largely unknown. The goal of this paper is to experimentally determine the biomechanical properties of the ankle-foot complex (i.e., the admittance) while performing a car-following task, thereby separating driver responses to visual feedback from those to designed haptic feedback. An experiment was conducted in a simplified fixed-base driving simulator, where ten participants were instructed to follow a lead vehicle, with and without the support of haptic feedback. During the experiment, the lead vehicle velocity was perturbed, and small stochastic torque perturbations were applied to the pedal. Both perturbations were separated in the frequency domain to allow the simultaneous estimation of frequency response functions of both the car-following control behavior and the biomechanical admittance. For comparison to previous experiments, the admittance was also estimated during three classical motion control tasks (resist forces, relax, and give way to forces). The main experimental hypotheses were that, first, the haptic feedback would encourage drivers to adopt a “give way to force task,” resulting in larger admittance compared with other tasks and, second, drivers needed less control effort to realize the same car-following performance. Time- and frequency-domain analyses provided evidence for both hypotheses. The developed methodology allows quantification of the range of admittances that a limb can adopt during vehicle control or while performing a variety of motion control tasks. It thereby allows detailed computational driver modeling and provides valuable information on how to design and evaluate continuous haptic feedback systems.

Haptic gas pedal feedback

Active driver support systems either automate a control task or present warnings to drivers when their safety is seriously degraded. In a novel approach, utilising neither automation nor discrete warnings, a haptic gas pedal (accelerator) interface was developed that continuously presents car-following support information, keeping the driver in the loop. This interface was tested in a fixed-base driving simulator. Twenty-one drivers between the ages of 24 and 30 years participated in a driving experiment to investigate the effects of haptic gas pedal feedback on car-following behaviour. Results of the experiment indicate that when haptic feedback was presented to the drivers, some improvement in car-following performance was achieved, while control activity decreased. Further research is needed to investigate the effectiveness of the system in more varied driving conditions. Haptics is an under-used modality in the application of human support interfaces, which usually draw on vision or hearing. This study demonstrates how haptics can be used to create an effective driver support interface.

Reduced Power Method: how to evoke low-bandwidth behaviour while estimating full-bandwidth dynamics

Many human motion control studies use system identification methods to estimate the human admittance (the frequency response function from force to position). Admittance was found to be affected by task instruction, environmental properties and perturbation properties. From literature it is known the frequency content (bandwidth) of the perturbation modulates the admittance, due to modulation of the reflexive feedback. However, reducing the perturbation bandwidth reduces the identifiable admittance bandwidth. Yet, the full dynamic range is necessary to understand the changes in control behaviour, and also to ensure accurate parametric fits of neuromusculoskeletal models to the estimated admittance. The goal of this study is to develop a perturbation signal that evokes low bandwidth control behaviour while it enables identification over the full admittance bandwidth. This study introduces the Reduced Power Method. Effectively, multisine torque perturbations are supplemented with reduced power (a small percentage of full power) beyond the perturbation bandwidth, large enough to allow accurate identification, and small enough not to influence control behaviour. The method was tested in an experimental study. The dynamic ankle control behaviour of subjects (n=10) was measured while performing a variety of tasks in face of continuous torque perturbations with and without the addition of reduced power. The estimated admittance varied substantially as a result of task instruction and perturbation bandwidth, but not as a result of the additional reduced power. In conclusion, the proposed method was successful in estimating the full dynamics of the admittance while the resulting control behaviour was adapted to the low-frequent full power perturbations.

Design of a Haptic Gas Pedal for Active Car-Following Support

The research presented in this paper focuses on the design of a driver support system for the manual longitudinal control of a car during car-following. The aim of the design was to develop a system that would cooperate with the driver in comfortably maintaining (safe) separation with a lead vehicle. Three important design issues for a haptic gas pedal feedback system can be distinguished: 1) quantification of intervehicle separation parameters; 2) the type of haptic feedback; and 3) the relation between haptic feedback and intervehicle separation. Because of the inverse relationship between time-to-contact (TTC) and time-headway (THW)-the smaller the THW, the more important the avoidance of high TTC-THW should act as an amplifier for the haptic gas pedal feedback based on TTC. Using gas pedal stiffness feedback is expected to better facilitate the manual control of intervehicle separation changes, quantified by THW and TTC, because stiffness feedback allows perception of force and force-slope changes. The force changes inform drivers of instantaneous changes in the environment. Force-slope changes prevent drivers from input to the car that would continue to reduce the following gap in situations where this would be undesirable. A review of fixed-base simulator and field tests confirms that haptic gas pedal feedback improves driver vigilance during car-following without increasing the workload.

Motivation for continuous haptic gas pedal feedback to support car following

The last years, increased effort has been dedicated to the design of systems that assist the driver in car following. The need for assistance systems arises from the fallibility of the visual feedback loop, for example due to inattention. Existing driver assistance systems either automate the car-following task or support drivers with binary warning systems to redirect their attention when necessary. The goal of this paper is to discuss the benefits and limitations of these systems, and to show the possibilities of an alternative design approach. To attain the goal, a theoretic analysis is presented, that views car following as a closed-loop control task that requires sufficient feedback about the separation (relative distance, relative velocity) to a lead vehicle. A task analysis helps to identify the areas where the current systems assist the driver well, and where they do not. The new design approach aims to keep the human in the loop, by supplementing the semi-continuous visual feedback loop with an additional continuous feedback loop, namely haptic feedback applied directly at the gas pedal. Expected benefits compared to existing systems include: better situation awareness (even during periods of visual inattention) and faster responses (the haptic feedback is available directly at the gas pedal, allowing the use of fast reflexes). Several design issues are presented, such as the prevention of nuisance and fatigue, deciding which separation states the feedback is based upon, and challenges in determining the correct characteristics of the haptic signals. The benefits of the approach are illustrated through several examples from literature that describe experimental humanin-the-loop studies with continuous haptic feedback. It is concluded that haptic feedback on the gas pedal is a promising way of supporting drivers.

The Impact of Haptic Feedback Quality on the Performance of Teleoperated Assembly Tasks

In teleoperation, haptic feedback allows the human operator to touch the remote environment. Yet, it is only partially understood to what extent the quality of haptic feedback contributes to human-in-the-loop task performance. This paper presents a human factors experiment in which teleoperated task performance and control effort are assessed for a typical (dis-)assembly task in a hard-to-hard environment, well known to the operator. Subjects are provided with four levels of haptic feedback quality: no haptic feedback, low-frequency haptic feedback, combined low- and high-frequency haptic feedback, and the best possible-a natural spectrum of haptic feedback in a direct-controlled equivalent of the task. Four generalized fundamental subtasks are identified, namely: 1) free-space movement, 2) contact transition, 3) constrained translational, and 4) constrained rotational tasks. The results show that overall task performance and control effort are primarily improved by providing low-frequency haptic feedback (specifically by improvements in constrained translational and constrained rotational tasks), while further haptic feedback quality improvements yield only marginal performance increases and control effort decreases, even if a full natural spectrum of haptic feedback is provided.

A Task-Specific Analysis of the Benefit of Haptic Shared Control During Telemanipulation

Telemanipulation allows human to perform operations in a remote environment, but performance and required time of tasks is negatively influenced when (haptic) feedback is limited. Improvement of transparency (reflected forces) is an important focus in literature, but despite significant progress, it is still imperfect, with many unresolved issues. An alternative approach to improve teleoperated tasks is presented in this study: Offering haptic shared control in which the operator is assisted by guiding forces applied at the master device. It is hypothesized that continuous intuitive interaction between operator and support system will improve required time and accuracy with less control effort, even for imperfect transparency. An experimental study was performed in a hard-contact task environment. The subjects were aided by the designed shared control to perform a simple bolt-spanner task using a planar three degree of freedom (DOF) teleoperator. Haptic shared control was compared to normal operation for three levels of transparency. The experimental results showed that haptic shared control improves task performance, control effort and operator cognitive workload for the overall bolt-spanner task, for all three transparency levels. Analyses per subtask showed that free air movement (FAM) benefits most from shared control in terms of time performance, and also shows improved accuracy.