Bernard Roth

Analysis of Multifingered Hands

This paper discusses three fundamental problems relating to grasping and manipulating objects within an articulated, multifingered hand: determining how hard to squeeze an ob ject in order to ensure a secure grasp, determining the finger- joint motions required to produce a desired motion of the object, and determining the workspace of the hand. Squeezing the object, or the application of internal grasp forces, is reduced to a linear programming problem which considers friction and joint torque limit constraints. The relationship between the finger-joint motions and the motion of the object, for the case of pure rolling between the finger tips and the object, is formulated as a set of differential equa tions. The total workspace for a hand is determinedfor spe cial cases of planar and spatial hands.

A New Actuation Approach for Human Friendly Robot Design

In recent years, many successful robotic manipulator designs have been introduced. However, there remains the challenge of designing a manipulator that possesses the inherent safety characteristics necessary for human-centered robotics. In this paper, we present a new actuation approach that has the requisite characteristics for inherent safety while maintaining the performance expected of modern designs. By drastically reducing the effective impedance of the manipulator while maintaining high-frequency torque capability, we show that the competing design requirements of performance and safety can be successfully integrated into a single manipulation system.

Playing it safe [human-friendly robots]

We have presented a new actuation concept for human-friendly robot design, referred to as DM/sup 2/. The new concept of DM/sup 2/ was demonstrated on a two-degree-of-freedom prototype robot arm that we designed and built to validate our approach. The new actuation approach substantially reduces the impact loads associated with uncontrolled manipulator collision by relocating the major source of actuation effort from the joint to the base of the manipulator. The emerging field of human-centered robotics focuses on application such as medical robotics and service robotics, which require close interaction between robotic manipulation systems and human beings, including direct human-manipulator contact. As a result, this system must consider the requirements of safety. To achieve safety we must employ multiple strategies involving all aspects of manipulator design.

Kinematics of a Hybrid Series-Parallel Manipulation System

In this paper we first derive the coordinate transformations associated with a three-degree-of-freedom in-parallel-actuated micro-manipulator. Then we combine these results with the transformations associated with an in-series three-axis wrist on which the in-parallel micro-manipulator is mounted. The results are the basic transformation equations between joint-space position variables and end-effector (or task space) position variables for a hybrid series/parallel six-degree-of-freedom manipulator system. This structural combination results in a manipulator which exhibits desirable fine and gross motion characteristics as both a stand-alone device or as a sub-system of a more complex system with redundant degrees of freedom. The forward and inverse position kinematics and rate and force decomposition for this hybrid six-degree-of-freedom linkage are presented.

A new actuation approach for human friendly robot design

Many successful robotic manipulator designs have been introduced. However, there remains the challenge of designing a manipulator that possesses the inherent safety characteristics necessary for human-centered robotics. In this paper, we present a new actuation approach that has the requisite characteristics for inherent safety while maintaining the performance expected of modern designs. By drastically reducing the effective impedance of the manipulator while maintaining high frequency torque capability, we show that the competing design requirements of performance and safety can be successfully integrated into a single manipulation system.

Inverse Kinematics of the General 6R Manipulator and Related Linkages

This paper elaborates on a method developed by the authors for solving the inverse kinematics of a general 6R manipulator. The method is shown to be applicable to determining the joint variables associated with all series-chain manipulators and closed-loop linkages constructed in a single loop with revolute, prismatic, or cylindric joints. The method is shown to yield a single polynomial, of minimum degree, in terms of just one of the joint variables. Once the roots of this polynomial are found, the remaining variables are then usually determined from linear sets of equations. It is shown that this method works equally well for general geometries and for special geometries such as those chararcterized by intersecting or parallel joint axes.

Localization of 5-HT2A receptors on dopamine cells in subnuclei of the midbrain A10 cell group

Considerable evidence suggests that a dysfunction of the dopamine and serotonin (5-hydroxytryptamine or 5-HT) neurotransmitter systems contributes to a diverse range of pathological conditions including schizophrenia, depression and drug abuse. Recent electrophysiological and behavioral studies suggest that 5-HT modulates dopaminergic neurons in the ventral tegmental area via activation of 5-HT(2A) receptors. It is currently unknown if 5-HT(2A) receptors mediate their actions on dopaminergic neurons in the ventral tegmental area via direct or indirect mechanisms. This study investigated whether 5-HT(2A) receptors were localized on dopamine cells within the A10 dopamine subnuclei of the rat, including the ventral tegmental area. We discovered that 5-HT(2A) receptor-like immunoreactivity colocalized with tyrosine hydroxylase, a marker for dopamine neurons, throughout the A10 dopamine cell population. Colocalization was most prominent in rostral and mid A10 regions, including the paranigral, parabrachial, and interfascicular subnuclei. Though more rare, non-dopaminergic neurons also expressed 5-HT(2A) receptor immunoreactivity in the ventral tegmental area. Additionally, although a dense population of 5-HT(2A) immunoreactive cells was observed in the rostral dorsal raphe nucleus, rarely were these cells immunoreactive for tyrosine hydroxylase. The linear raphe A10 dopamine subdivisions also displayed a low degree of 5-HT(2A) receptor and tyrosine hydroxylase colocalization. These findings provide an anatomical basis for the physiological modulation of dopamine neurons in the rostral ventral tegmental area either directly, by 5-HT(2A) receptors localized on dopamine cells, or indirectly, through a non-dopaminergic mechanism. Interestingly, 5-HT(2A) receptors were expressed on dopamine neurons in several A10 subnuclei that project to mesolimbic forebrain regions implicated in drug addiction, and recent evidence indicates that ventral tegmental area 5-HT(2A) receptor activation may modulate reward-related behavior in rodents. 5-HT(2A) receptors were also expressed on dopamine cells in A10 subnuclei that project to forebrain areas that have been implicated in schizophrenia, and atypical antipsychotic drugs have high affinities for 5-HT(2A) receptors. Thus, findings in this study could have important implications for understanding 5-HT and dopamine circuitry dysfunction in schizophrenia.

Clozapine and other 5-hydroxytryptamine-2A receptor antagonists alter the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro and in vivo

In this study, we demonstrate that clozapine and other atypical antipsychotic drugs induce a paradoxical internalization of 5-hydroxytryptamine-2A receptors in vitro and a redistribution of 5-hydroxytryptamine-2A receptors in vivo. We discovered that clozapine, olanzapine, risperidone and the putative atypical antipsychotic drug MDL 100,907 all induced 5-hydroxytryptamine-2A receptor internalization in fibroblasts stably expressing the 5-hydroxytryptamine-2A receptor in vitro. Two 5-hydroxytryptamine-2A antagonists (mianserin and ritanserin), which have been demonstrated to reduce negative symptoms in schizophrenia, also caused 5-hydroxytryptamine-2A receptor internalization. Four different drugs, each devoid of 5-hydroxytryptamine-2A antagonist activity, had no effect on the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro. Treatment of rats for seven days with clozapine induced an increase in intracellular 5-hydroxytryptamine-2A receptor-like immunoreactivity in pyramidal neurons, while causing a decrease in labeling of apical dendrites in the medial prefrontal cortex. This redistribution of 5-hydroxytryptamine-2A receptors in pyramidal neurons was also seen when rats were chronically treated with another atypical antipsychotic drug, olanzapine. The typical antipsychotic drug haloperidol, however, did not induce a redistribution of 5-hydroxytryptamine-2A receptors in pyramidal neurons in the medial prefrontal cortex. Taken together, these results demonstrate that several atypical antipsychotic drugs with high 5-hydroxytryptamine-2A receptor affinities induce a redistribution of 5-hydroxytryptamine-2A receptors both in vivo and in vitro. It is conceivable that the loss of 5-hydroxytryptamine-2A receptors from the apical dendrites of pyramidal neurons is important for the beneficial effects of atypical antipsychotic drugs and other 5-hydroxytryptamine-2A antagonists in schizophrenia.

Synthesis of Path-Generating Mechanisms by Numerical Methods

Algebraic methods in kinematic synthesis are extended to cases in which the development of iterative numerical procedures are required. Algorithms are developed for the numerical solution of nonlinear, simultaneous, algebraic equations. Convergence is obtained without the need for a “good” initial approximation. The theory is applied to the nine-point path synthesis of geared five-bar motion, in terms of which four-bar motion may be considered as a special case.

On the spatial motion of a rigid body with point contact

This paper is an extension to the 3-dimensional case of our previous work on planar motion with point contact [2]. Here we study the so called roll-slide spatial motions. Such motions occur whenever point contact between bodies is maintained under spatial motion. We consider instantaneous time-based kinematics and assume the presence of a tactile sensor to measure the relative motion at the point of contact. It is indicated how the derived kinematic relationships can be applied to sensor based robotic path planning.