An advanced backhoe user interface has been developed which uses coordinated control with haptic feedback. Results indicate that the coordinated control provides more intuitive operation that is easy to learn, and the haptic feedback also relays meaningful information back to the user in the form of force signals from digging forces and system limitations. However, results show that the current system has significant problems with biodynamic feedthrough, where the motion of the controlled device excites motion of the operator, resulting in undesirable forces applied to the input device and control performance degradation. This unwanted input is difficult to decouple from the intentional operator input in experiments. This research presents an investigation on the effects of biodynamic feedthrough on this particular backhoe control system, using system identification to empirically define models to represent each component. These models are used for a preliminary simulation study on potential methods for biodynamic feedthrough compensation.
This research investigates and seeks to mitigate the undesirable effects of biodynamic feedthrough in backhoe operation. Biodynamic feedthrough occurs when motion of the controlled machine excites motion of the human operator, which is fed back into the control input device. This unwanted input can cause significant performance degradation, which can include limit cycles or even instability. Backhoe user interface designers indicate that this is a problem in many conventional machines, and it has also proved to degrade performance in this testbed. A particular backhoe control system, including the biodynamic feedthrough, is modeled and simulated. Cab vibration control is selected as a means to mitigate the biodynamic feedthrough effect. Two controller based methods are developed based on these models and presented, both of which use the working implement itself to reduce the cab motion. In this case, the backhoe arm has dual functionality, to perform excavation operations and to cancel cab vibration. Results show that significant reductions in cab motion can be obtained with minimal tracking performance degradation, without additional actuators.
Biodynamic feedthrough can occur in many types of human-controlled machines where the operator is also a passenger. The motion of the controlled machine excites motion of the human operator's body, causing motion of the operator's hand, creating undesirable input. Backhoes are one example of a machine that is susceptible to significant performance degradation from biodynamic feedthrough. This study investigates and models the system dynamics, including the human operator and biodynamic feedthrough, develops two methods of compensation for biodynamic feedthrough based on those models, compares them with similar controllers without vibration compensation, and experimentally validates the performance of the biodynamic feedthrough compensation. The performance results, as well as operator survey results, show that the operators perform better and prefer the vibration-compensating controllers over their non-vibrationcompensating counterparts.
This paper describes the development of a hydraulically actuated patient transfer device, utilizing a force amplifying passivity based control strategy. The patient transfer device is intended for moving mobility limited patients, for example, from a bed to a chair, from a wheelchair into a car, or from the floor into a wheelchair. Our needs assessment has indicated that a more powerful, more easily maneuverable device is needed which is operable by a single caregiver with one hand. For this purpose, we are proposing a coordinated force amplifying control strategy. The caregiver input to the device is measured from a force sensor mounted on the device near the patient. The output is the force applied by the device actuators in the same direction as the input; this force may be amplified to assist the caregiver. Passivity-based control provides a way to implement this force amplifying control to aid in stability, which is critical for a device that interacts directly with humans. This paper describes the implementation of this force amplifying passivity-based control on a simpler pre-prototype two DOF patient transfer device.
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