A nonlinear feedback scheme for a gravity-assisted underactuated manipulator with second-order nonholonomic constraints is presented in this paper. The joints of the hyper articulated arm have no dedicated actuators but are activated by gravity. By tilting the base link appropriately, the gravitational torque drives the unactuated links to a desired angular position. With simple locking mechanisms, the hyperarticulated arm can change its configuration using only one actuator at the base. This underactuated arm design was motivated by the need for a compact snake-like robot that can go into aircraft wings and perform assembly operations using heavy end-effectors. The dynamics of the unactuated links are essentially second-order nonholonomic constraints for which there are no general methods to design closed-loop control. We propose a nonlinear closed-loop control law that is guaranteed to be stable in positioning one unactuated joint at a time. We synthesize a Lyapunov function to prove the convergence of this control scheme. The Lyapunov function also generates estimates of the domain of convergence of the control law for various control gains. The control algorithm is implemented on a prototype three-link system. Finally, we provide some experimental results to demonstrate the efficacy of the control scheme.

This paper presents algorithms for concurrent deployment of multiple links of a gravity-assisted underactuated robot arm. The joints of the hyper-articulated arm have no dedicated actuators, but are activated with gravity. By tilting the base link appropriately, multiple unactuated links may be steered simultaneously to desired angular positions. This underactuated arm design was motivated by the need for a compact snake-like robot that can go into aircraft wings and perform assembly operations using heavy end-effecters. The dynamics of the unactuated links are essentially 2ndorder non- holonomic constraints, for which there are no general control algorithms. We perform a controllability analysis to establish the feasibility of multi-link positioning using the available inputs, viz., the biaxial tilts of the base link. We propose a feed-forward control algorithm for simultaneous positioning of multiple links. We also propose an intermittent feedback control scheme to compensate for disturbances acting on the system. We built a 4 link prototype where the base is tilted using a Stewart Platform. The proposed control schemes are implemented on our prototype system. The experimental results indicate the efficacy of the control schemes.

Precise robot positioning is important for many applications in indoor environments. Current solutions to the indoor localization problem are either both unreliable and inaccurate, or very expensive. In this paper we propose, design and build a low-cost, robust and accurate indoor localization system using laser light sources. The system calculates the coordinates of a robotic arm by using triangulation algorithms with precisely measured values of the angles of the receiver with respect to the three laser emitters. A system of three rotating lasers and receiver unit was built and deployed in the wing of an aircraft. Using this system, a robotic arm could be localized accurately within error margins defined approximately by Gaussian distributions centered at the object’s true coordinate values and with standard deviations of 0.19 mm, 0.11 mm and 0.34 mm in the x, y and z coordinate directions respectively. The system was also used to detect vertical drop in the robotic arm due to its weight as it extends to perform fitting operations on the skin of the wing. Feedback from the laser localization system was used to adjust the position of the tip of the robotic arm in order to perform a sequence of high precision docking tasks within the aircraft wing

We propose a novel concept for the actuation of a hyper-articulated robot arm for assembly operations inside an aircraft wing-box. Traditional electromechanical actuators powering individual joints are unsuitable for our purpose, because of limited space and large payload requirements. We propose an underactuated system which uses a single actuator at the base for the deployment of a multi d.o.f. serial linkage structure. Our proposed system exploits gravitational and gyroscopic torques in the system dynamics to rapidly deploy the system. There are no general techniques for the control of such underactuated systems. We develop and compare two approaches for determining the input required for a desired output trajectory and verify the results through simulation and experiments

We present a design concept and two initial prototypes of a robot arm for assembly operations inside an aircraft wing-box. The wing-box has a large span, but is only accessible through multiple small portholes along its length. The arm is compact enough to enter the wing-box through the small portholes and is capable of subsequent reconfiguration so as to access a number of assembly points inside the wing-box. Traditional electromechanical actuators are unsuitable for our purpose, because of limited space and large payload requirements. We use an actuator module comprising Shape Memory Alloy (SMA) wires, which are known for their high stress to volume ratio. Our design also addresses the issue of limited strain of SMA wires through a displacement amplification mechanism. Our compact, high displacement actuator module can be readily integrated into the structure of the robot arm. We also discuss a deployment scheme for the robot arm, which eliminates gravity loading during the reconfiguration phase, and also helps to position the end effecter at the various assembly points inside the wing-box.

We propose a novel concept for the actuation of a hyper-articulated robot arm for assembly operations inside an aircraft wing-box. The wing-box has a large span, but is only accessible through multiple small portholes along its length. The arm should be compact enough to enter the wing-box through the small portholes, yet capable of subsequent reconfiguration so as to access a number of assembly points inside the wing-box. Traditional electromechanical actuators powering individual joints are unsuitable for our purpose, because of limited space and large payload requirements. We propose an underactuated system which uses a single actuator at the base for the deployment of a multi d.o.f. serial linkage structure. Our proposed system exploits gravitational and gyroscopic torques in the system dynamics to rapidly deploy the system. We develop a methodology for determining the input required for a desired output trajectory and verify the results through simulation.

A new method for repositioning a rigid body with a flexible sheet is developed and is applied to a rehabilitation bed for turning and transferring a bedridden patient to alleviate bedsores and other ailments. The patient position and orientation are fully controlled by manipulating a flexible bed sheet under no-slip conditions. The use of a flexible sheet and the untethered nature of manipulation make the repositioning method particularly well suited to handling the human body. First, the basic design concept of the rehabilitation bed for automated patient repositioning is presented. The kinematic and static behaviors of body-sheet interactions are analyzed, and conditions for no-slip, quasi-static repositioning are obtained. In order to prevent injury to the patient's fragile skin, it must be ensured that the patient does not slip on the sheet during repositioning. A prototype bed with a pair of servoed arms for manipulating the bed sheet is developed, and the no-slip conditions and the repositioning method are experimentally verified. A closed-loop control based on the measurement of a patient's position and orientation is implemented and tested. Note to Practitioners-This work was motivated by the problems faced by bedridden patients as well as caregivers in the healthcare industry. The labor-intensive repositioning and transfer of bedridden patients are performed with a robotic system supervised by a single caregiver. Our repositioning scheme uses the bed sheet for rolling and moving the patient and closely mimics the current practice prevalent in nursing homes and hospitals. Our approach will be a natural alternative to manual repositioning and transfer and will be acceptable for most caregivers and patients. Initial prototyping and experiments have been completed in consultation with a professional caregiver.

Long hours of driving cause the tissues to be pressurized for an extended period and result in considerable discomfort and driver fatigue. Periodically stimulating the tissues in contact with the car seat, as well as providing adequate ventilation and pressure relief may alleviate these problems. In this paper, we describe the design of a robotic car seat capable of actively redistributing the contact pressure on the tissue and thus providing relief to the weary driver. The distributed nature of the surface actuation and space limitations necessitate the use of a large number of actuators that must be confined to a small volume. We design and use Shape Memory Alloy actuator units, which can accomplish the above goals by virtue of their high power to weight ratio. Matrix architecture is used for the drive amplifier that can drive N/sup 2/ actuator units using only 2N switches and is thus suitable for vast degree of freedom systems in terms of scalability. The prototype car seat uses 16 SMA actuator units, which are driven in a matrix architecture using 8 switches. The actuators are compactly housed under the car seat and the force and displacements are transmitted to the flexible seat surface through a novel routing scheme. We create a distributed lifting motion of the seat surface in order to stimulate the tissue. A complementary distributed sinking motion of the seat surface is created in order to provide pressure relief and ventilation.

The marionette bed presents a new method for rolling and repositioning a bedridden patient using a pair of actuated rollers attached to both sides of the bedsheet in order to lift and manipulate the patient body. This prevents development of painful bedsores and of pneumonia. This paper builds a simple kinematic model to create trajectories for generation of desired body motion. It also addresses a closed loop control strategy, based on patient position and orientation feedback, for the marionette bed. Closed loop control provides flexibility and safety in the various modes of operation of the bed. The bed can now handle patients of various sizes when supplied with some parameters. The safety of the patient is also ensured because the position and orientation is continuously monitored. A prototype is built and initial experiments demonstrate that a human body is rolled and manipulated by the assist device, as desired.

A new method for manipulation of a rigid body with a flexible sheet is presented, and the method is applied to repositioning of bedridden patients. A key feature of the proposed system is that the body is not securely connected to the sheet and the contact region between the body and the sheet changes dynamically during manipulation. The use of a soft flexible sheet and the untethered nature of manipulation, makes the system particularly well suited to handling the human body. We present an application to a rehabilitation bed for repositioning a bedridden patient to alleviate secondary ailments such as bedsores. In order to prevent injury to the patient's fragile skin, it must be ensured that the patient does not slip on the sheet during repositioning. We model the system and present a no-slip condition based on system parameters. The model is used to develop a closed loop control strategy for coordinating the motions of multiple actuators of the prototype bed. The prototype bed can successfully reposition test subjects using the control strategy developed.