Leg Lift During Non-Overconstrained Pseudo-Static Walking

A non-overconstrained pseudo-static walking machine has 1 leg joint under position control for every degree-of-freedom of the body. When 1 joint is position controlled on each of 6 legs, leg lift during a step results in 1 unregulated degree-of-freedom of the body. A second joint in one of the 5 legs that maintain contact with the ground must be switched to active position control at the same time that a foot is lifted. In theory any passively controlled joint in the 5 supporting legs may be chosen. However the requirement that no leg be in tension and practical limits on torques available from joint actuators severely restrict choice of both additional joint to actively position control and possible body positions where legs can be lifted.

A Methodology for the Configuration Synthesis of Machining Centers With Automatic Tool Changer

The purpose of this paper is to present a design methodology for the configuration synthesis of machining centers with automatic tool changer to meet the required topology and motion characteristics. According to the concept of coordinate systems, graph theory, generalization, specialization, and motion synthesis, this design methodology is proposed and computerized, and the machining centers with automatic tool changer up to eight links are synthesized. As the result, for the machining centers with drum type tool magazine, the numbers of configurations of machining centers with 6, 7, and 8 links are 2, 13, and 20, respectively. And, for the machining centers with linear type tool magazine, the numbers of configurations of machining centers with 5, 6, 7, and 8 links are 1, 5, 20, and 60, respectively. Furthermore, this work provides a systematic approach for synthesizing spatial open-type mechanisms with topology and motion requirements.

A Proposed Model for Stochastic Vibration Analysis of Gear Transmission Systems

A new mathematical model is presented for analyzing the vibration of gear transmission systems with consideration of the influence of the time-variant stiffness, loads, gear transmission errors. The gear transmission system is modeled as a non-linear, time-correlated and stationary stochastic system. The transmission errors of gears are decomposed into harmonic and random components in terms of the different characteristics of their spectrums. The random component is simulated by a second order Markov process. A simulation system for vibration analysis of gear transmission systems is then developed, based on this new model. The input to this system is a Guassian white noise process and harmonic errors, and the output is the rotational vibration acceleration of gears. Some experiments are conducted to verify the proposed model. By comparing the results generated from the simulation system with those from the experiments, the proposed model is found to reach a fairly good accuracy, and thus the model is useful in designing gear transmission systems with the objective to reduce the vibration and noise of the systems in operation.

Acceleration Analysis of Platform-Type Manipulators

The screw algebra is used to efficiently derive expressions in compact form for both the angular accelerations of the moving links and the linear accelerations of points on the links of platform-type manipulators. The analysis employs the property that the acceleration state of the manipulator platform can be determined by considering the acceleration states of the links of only one — any one — of the manipulator legs. The obtained expressions provide an ease in symbolic and algebraic manipulation. The analysis is then extended to specify the acceleration center point of ithe nstantaneous motion of the manipulator platform. The acceleration center point is then used in expressing the distribution of the acceleration field of the platform instant motion which is important in manipulator synthesis. The special case of planar manipulators is studied and simpler expressions are derived. Numerical examples are presented for the analysis of a 3-DOF planar platform-type and of a 6-DOF spatial “Stewart Platform” manipulators to illustrate the analysis procedure.

On Force and Motion Control of Serial-Parallel Robots

A serial-parallel robot has the high stiffness and accuracy of a parallel robot, and a large workspace and compact structure of a serial robot. In this paper, the resolved force control algorithm is derived for serial-parallel robots, including a 3-articulated-arm platform robot, a linkage robot, and two cooperating serial robots. A S matrix is derived to relate joint torque to the external load. Using the principle of virtual work, S is used in resolved rate control algorithm to relate the tool velocity to joint rate. S can be easily expanded to the control of redundant actuation, and it can be used to interpret singularity. MATLAB is used to verify these control algorithms with graphical motion animation.

Synthesis of Non-Uniform Stroke Piston Engines

Piston engines have generally been designed with strokes that are uniform throughout the engine cycle. Variable-stroke engines have been designed with the capability to change the stroke lengths from cycle to cycle depending on load requirement. This article examines the synthesis of piston engines that are designed to have different stroke lengths and different relative stroke timing over an engine cycle. Such piston trajectories have been found to exhibit very high thermal efficiencies without resorting to high compression ratios. An investigation into different mechanisms and approaches toward the synthesis of such engine mechanisms is presented.

Kinematic Geometry of Wheeled Vehicle Systems

This paper addresses instantaneous motion characteristics of wheeled vehicles systems on even and uneven terrain. A thorough kinematic geometric approach which utilizes screw system theory is used to investigate vehicle-terrain combinations as spatial mechanisms that possess multiple closed kinematic chains. It is shown that if the vehicle-terrain combination satisfies certain geometric conditions, for instance when the vehicle operates on even terrain, the system becomes singular or non-Kutzbachian — it possesses finite range mobility that is different from the one obtained using Kutzbach criterion. An application of this geometric approach to the study of rate kinematics of various classes of wheeled vehicles is also included. This approach provides an integrated framework to study the kinematic effects of varying the vehicle and/or terrain geometric parameters from their nominal values. In addition, design enhancements of existing vehicles are suggested using this approach. This kinematic study is closely related to the force distribution characteristics of wheeled vehicles which is the subject of the companion paper [SN96].

Construction of a Six-Degrees-of-Freedom Parallel Manipulator With Three Planarly Actuated Links

The construction of a new type of a six-degrees-of-freedom parallel robot is presented in this paper. Coordinated motion of three planar motors, connected to three fixed-length links, produces a six-degrees-of-freedom motion of an output link. Its extremely simple design along with much larger work volume make this high performance-to-simplicity ratio robot very attractive.

A New Approach for Curvatures of Conjugate Surfaces

A new and general approach for curvatures of conjugate surfaces is provided in this paper. The main characteristic of the approach is that relative curvatures and geodesic torsions of the conjugate surfaces are directly calculated in terms of the normal curvatures and geodesic torsions of the generating surface on two non-orthogonal tangents of surface curvilinears in global surface system. In comparison with the current approaches that use two orthogonal tangents or the principal directions in local system at each calculating point, the approach developed in this paper has a simple calculating process and a simple computer program. Based on the curvature equations, sliding velocities and sliding ratios of the conjugate surfaces are studied. The approach is illustrated by a numerical example of a plane enveloping globoidal wormgear drive.

A New Method for Displacement Analysis of Multi-Loop Spatial Linkages Based on Ordered Simple-Opened-Chains

This paper presents systematically a new method for the displacement analysis (DA) of multi-loop spatial linkages (MLSLs) based on ordered simple-opened-chains (SOCs). In performing DA, a MLSL is converted into not a set of base points, a set of isolated links or a tree with/without isolated links in common use, but a weakly coupled MLSL in this paper. The characteristics of the proposed method are: (a) The number of unknowns in the set of equations for displacement analysis (EDA) of a MLSL is reduced to the minimum; (b) All the possible configurations corresponding to a given set of inputs of a weakly coupled MLSL or a strongly coupled MLSL with the coupled degree k = 1 can be obtained quickly. As compared with the other two methods available to find all the solutions to the DA in the case of MLSL with k = 1, the proposed method is superior to the resultant method in that it is applicable to more complex MLSLs and superior to the continuation method in that it takes much less CPU time to find all the solutions; (c) The set of EDA can be formulated and solved automatically; and (d) The new approach makes it possible to perform the kinematic and kineto-static analyses in a unified and simplified way.