Hybrid control strategies for a five-finger robotic hand

This paper presents a hybrid controller of soft control techniques, adaptive neuro-fuzzy inference system (ANFIS) and fuzzy logic (FL), and hard control technique, proportional-derivative (PD), for a five-finger robotic hand with 14-degrees-of-freedom (DoF). The ANFIS is used for inverse kinematics of three-link fingers and FL is used for tuning the PD parameters with 2 input layers (error and error rate) using 7 triangular membership functions and 49 fuzzy logic rules. Simulation results with the hybrid of FL-tuned PD controller exhibit superior performance compared to PD, PID and FL controllers alone.     

Arches of the hand in reach to grasp

Topographically, the hand is described by its anterior (palmar) and posterior (dorsal) surfaces that encompass a hollow cavity that changes its shape during hand preshaping and grasping according to the object to be grasped. The hollow cavity has been described as consisting of three arches that run in different directions: transverse, longitudinal and oblique, spanning the anterior surface of the hand. Although described anatomically, the modulation in the palmar arches has not been investigated kinematically during actual grasping. In this study, we describe and compare biomechanical formulations of the palmar arch, specifically, the distal transverse and the oblique arches. In addition, we introduce another biomechanical formulation of the palmar arch, called the kinematic transverse arch that takes account of the thenar and hypothenar involvement in arch formation. Hand shape modulation during two natural power-grasping tasks was studied in eight healthy adults. Results showed a significant influence of the overall contribution of thenar and hypothenar movement during hand shape modulation. While there was relatively more thenar contribution during transport shaping, more hypothenar contribution was evident during preshaping and contact shaping-the two phases of grasping during which the hand establishes contact with the object. The advantage of the new formulation is that it better described the contributions from thenar and hypothenar movement to palmar arch formation which may be a more accurate depiction of hand preshaping during grasping.     

Human control of a simple two-hand grasp

We investigated how people control fast, accurate movements of a load using a simple two-hand grasp. By providing a clear instruction to several subjects, we isolated a single control strategy. The kinematics produced by this control strategy are nearly indistinguishable from those produced during single-hand movements, but the torques are quite different: one hand accelerates not only itself, but also the load and the other hand, while the other hand brakes the hand-load-hand system. As a result, the hands squeeze the load with a large force during the movement.The dynamics of the hand-load-hand system are of the same form as the dynamics of a single-hand system. Apparently, by taking advantage of this dynamic similarity and of the spring-like properties of muscle, the human motor control system can control the two-hand grasp system simply by modifying the muscle activation patterns used to control single-hand movements.The task dynamics of two-hand grasp do not require that the load be squeezed during the movement, and squeezing the load wastes torque that could be used to move more quickly. However, the human motor control system may choose this squeezing strategy because it reliably brakes the hand-load-hand system despite inherent variability in the braking of individual hands.     

Cortical control of grasp in non-human primates

The skilled use of the hand for grasping and manipulation of objects is a fundamental feature of the primate motor system. Grasping movements involve transforming the visual information about an object into a motor command appropriate for the coordinated activation of hand and finger muscles. The cerebral cortex and its descending projections to the spinal cord are known to play a crucial role for the control of grasp. Recent studies in non-human primates have provided some striking new insights into the respective contribution of the parietal and frontal motor cortical areas to the control of grasp. Also, new approaches allowed investigating the coupling of grasp-related activity in different cortical areas for the control of the descending motor command.     

Nonlinear control of bioreactors with input multiplicities

Control of bioreactors exhibiting two input multiplicities, i.e., steady-state gains having opposite sign, is theoretically analyzed. The nonlinear system is represented by a unity gain linear system cascaded with a nonlinear gain. A conventional PI controller designed for the linear portion of the system followed by the solution of the nonlinear gain equation gives a nonlinear controller. The performance of the nonlinear controller is compared with that of the linear PI controller designed for the overall linear system. The nonlinear PI controller performance is superior to that of the linear PI controller.     

Bio-inspired design strategies for central pattern generator control in modular robotics

New findings in the nervous system of invertebrates have shown how a number of features of central pattern generator (CPG) circuits contribute to the generation of robust flexible rhythms. In this paper we consider recently revealed strategies that living CPGs follow to design CPG control paradigms for modular robots. To illustrate them, we divide the task of designing an example CPG for a modular robot into independent problems. We formulate each problem in a general way and provide a bio-inspired solution for each of them: locomotion information coding, individual module control and inter-module coordination. We analyse the stability of the CPG numerically, and then test it on a real robot. We analyse steady state locomotion and recovery after perturbations. In both cases, the robot is able to autonomously find a stable effective locomotion state. Finally, we discuss how these strategies can result in a more general design approach for CPG-based locomotion.     

Nonlinear feedforward control of bioreactors with input multiplicities

A steady-state nonlinear feedforward controller (FFC) for measurable disturbances is designed for a continuous bioreactor, which is represented by Hammerstein type nonlinear model wherein the nonlinearity is a polynomial with input multiplicities. The manipulated variable is the feed substrate concentration (S_f) and the disturbance variable is the dilution rate (D). The productivity (Q=DP) is considered as the controlled variable. The desired value of Q=3.73 gives two values of feed substrate concentration. The nonlinearity in the gain is considered for relating output to the manipulated variable and separately for the relation between output to disturbance variable. The FFC is also designed for the overall linearized system. The performance of the FFC is evaluated on the nonlinear differential equation model. The FFC is also designed for the model based on a single nonlinear steady-state equation containing both D and S_f. This nonlinear FFC gives the best performance. The nonlinear FFC is also designed by using only linear gain for the disturbance and nonlinear gain for the manipulated variable. Similarly, nonlinear FFC is also designed by using linear gain for the manipulated variable and the nonlinear gain for the disturbance variable. The performances of these FFC schemes are compared.     

Optomotor course control in flies with largely asymmetric visual input

We have studied freely flying and walking flies as well as flies flying in a flight simulator in order to discover how functionally blinding one of the eyes affects the fly's ability to move straight. It is hard to tell just by observing the animals' movements whether they have been deprived of vision in one eye. Statistical analysis is need to show that there are differences in the locomotory paths of monocular and binocular flies: monocular flies tend to turn slightly towards the side of the seeing eye. It is possible that the superimposed translational and rotational optic flow fields, generated on the trajectory of monocular flies, sum to zero net flow. This overall flow over the retina of the open eye might lead to a state of optomotor equilibrium. Accepted: 11 October 1999     

Nonlinear control of bioreactors with input multiplicities in dilution rate

Control problems of continuous bioreactors having two input multiplicities in dilution rate on the productivity are analyzed. The nonlinear system is represented by a unity gain linear subsystem cascaded with a nonlinear gain subsystem. A conventional PI controller designed for the linear subsystem followed by the solution of the nonlinear gain equation gives a nonlinear controller. The performance of the nonlinear controller is compared with that of the conventional PI controller and also of the nonlinear controller [1] designed based on the output equation. The present nonlinear PI controller gives a superior performance. A single set of controller settings can be used for both the operating points. Whereas the linear PI controller and the nonlinear controller proposed by Henson and Seborg [1] destabilize the system.     

Prehensile control of a hand prosthesis by a microcontroller

The functional replacement of a natural hand and wrist is usually achieved by a split hook or an electrically powered and myoelectrically controlled artificial hand with one degree of freedom. In contrast to the commercial devices, this paper describes an experimental hand with four electric motors, nineteen sensors, and control algorithms which are written for a microcontroller. The hand significantly improves the prehension capabilities of an artificial device and leads to a design which is easily controlled by a user as it mimics the control system of the natural hand.     

Visuo-motor control: giving the brain a hand

Sensory information is acquired in spatial coordinate systems linked to sense organs, yet movement must be executed in coordinate systems linked to motor effector organs. Neurophysiological experiments are yielding new insights into how the brain transforms coordinate systems to facilitate movement.     

Distributed power and control actuation in the thoracic mechanics of a robotic insect

Recent advances in the understanding of biological flight have inspired roboticists to create flapping-wing vehicles on the scale of insects and small birds. While our understanding of the wing kinematics, flight musculature and neuromotor control systems of insects has expanded, in practice it has proven quite difficult to construct an at-scale mechanical device capable of similar flight performance. One of the key challenges is the development of an effective and efficient transmission mechanism to control wing motions. Here we present multiple insect-scale robotic thorax designs capable of producing asymmetric wing kinematics similar to those observed in nature and utilized by dipteran insects to maneuver. Inspired by the thoracic mechanics of dipteran insects, which entail a morphological separation of power and control muscles, these designs show that such distributed actuation can also modulate wing motion in a robotic design.     

A physiological basis for control of a prosthetic hand

Recent surveys from upper limb amputees indicate the sentiment that prosthetic hands do not function in a life-like manner and are not intuitively controlled. Thus, two methods of control for a prosthetic hand are presented. A proportional derivative (PD) force controller is compared to a novel biomimetic application of sliding mode control. The biomimetic sliding mode (BSM) controller was designed to map human muscle signals into prosthesis motor command signals in a physiologically expected manner.The BSM and PD controllers were evaluated analytically and subjectively by one amputee and nine nonamputee test subjects. The posture of the hands of the nonamputee test subjects were measured with a CyberGlove and used to determine if the position of the prosthesis (when driven by both controllers) was highly correlated to the posture of the human hands. Force tracking experiments were also performed by all test subjects with both controllers to evaluate the ability to control the applied force. Finally, a dual object lifting task was performed by all test subjects to determine if the mapping of electromyogram (EMG) signals with the BSM controller resulted in physiologically expected motions. A nonparametric Mann–Whitney U-test was performed on the subjective evaluations to determine the statistical significance of the evaluations.The BSM controller was shown to replicate the posture of the human hand much more accurately than the PD force controller. The BSM controller also enabled better average force tracking results and higher success rates with the dual object lifting experiment while the same task was nearly impossible to perform with the PD controller. Finally, the BSM controller was subjectively rated to be more similar to control in comparison to the human hand with respect to position and force.     

Rapid disappearance of a massive iatrogenic haematoma of the left hand following radial coronary angiogram

A 73-year-old man with a medical history of coronary artery disease and status post coronary artery bypass grafting underwent elective coronary angiography for progressive left ventricular systolic dysfunction using the radial artery access.     

Engineering synthetic signaling proteins with ultrasensitive input/output control

Many signaling proteins are built from simple, modular components, yet display highly complex signal-processing behavior. Here we explore how modular domains can be used to build an ultrasensitive switch--a nonlinear input/output function that is central to many complex biological behaviors. By systematically altering the number and affinity of modular autoinhibitory interactions, we show that we can predictably convert a simple linear signaling protein into an ultrasensitive switch.     

Song-selective auditory input to a forebrain vocal control nucleus in the zebra finch

Neurons in nuclei on the motor pathway for vocalizations in songbirds are known to responses in one such nucleus, robustus archistriatalis (RA), were characterized by making multi-unit recordings in awake and anesthetized adult male zebra finches and in birds that had received lesions of the input to RA from the lateral part of the magnocellular nucleus of the anterior neostriatum (LMAN) or the Higher Vocal Center (HVC). In awake birds, RA neurons have a high level of spontaneous activity and vigorous auditory responses to song stimuli. Significantly greater responses are seen to the bird's own song (BOS) than to BOS played in reverse (REV) or to the songs of conspecifics (CON). Under ketamine-xylazine anesthesia, spontaneous activity is reduced, response latency increases and responses to BOS, REV and CON are indistinguishable. Responses obtained under urethane anesthesia are similar to those seen in awake birds. Thus, the pattern and selectivity of auditory responses in RA depend on the animal's state. Auditory responses in RA are qualitatively unchanged following lesion of the input to RA from LMAN, indicating that this pathway is not required for the sensory processing that underlies the preference for BOS on the vocal production pathway. Our results show that an input other than that from LMAN must be primarily responsible for auditory responses in RA. The direct projection form HVC is the most likely pathway by which song selective auditory information arrives in RA, since lesioning HVC abolished auditory responses in RA. © 1993 John Wiley & Sons, Inc.     

Learning to walk with a robotic ankle exoskeleton

We used a lower limb robotic exoskeleton controlled by the wearer's muscle activity to study human locomotor adaptation to disrupted muscular coordination. Ten healthy subjects walked while wearing a pneumatically powered ankle exoskeleton on one limb that effectively increased plantar flexor strength of the soleus muscle. Soleus electromyography amplitude controlled plantar flexion assistance from the exoskeleton in real time. We hypothesized that subjects' gait kinematics would be initially distorted by the added exoskeleton power, but that subjects would reduce soleus muscle recruitment with practice to return to gait kinematics more similar to normal. We also examined the ability of subjects to recall their adapted motor pattern for exoskeleton walking by testing subjects on two separate sessions, 3 days apart. The mechanical power added by the exoskeleton greatly perturbed ankle joint movements at first, causing subjects to walk with significantly increased plantar flexion during stance. With practice, subjects reduced soleus recruitment by approximately 35% and learned to use the exoskeleton to perform almost exclusively positive work about the ankle. Subjects demonstrated the ability to retain the adapted locomotor pattern between testing sessions as evidenced by similar muscle activity, kinematic and kinetic patterns between the end of the first test day and the beginning of the second. These results demonstrate that robotic exoskeletons controlled by muscle activity could be useful tools for testing neural mechanisms of human locomotor adaptation.