Win-Bin Shieh

Design of Statically Balanced Planar Articulated Manipulators With Spring Suspension

This paper proposes a design methodology for the synthesis of statically balanced planar articulated manipulators through direct spring installation. The proposed method can determine all admissible configurations of spring installation with a given planar articulated manipulator. The fundamental principle for gravity balance of a conservative system of spring-gravity is formulated by a stiffness block matrix, wherein each component matrix implies interacting forces among the links. The distribution of nonzero-component matrices can be related to a type of spring configuration. The minimum number of springs that are required for a statically balanced manipulator can be further determined, based on the number of design parameters and the number of simultaneous equations derived from the zero-component matrices of stiffness block matrix. By the representation of conventional adjacency matrix for connectivity of springs among the links, five characteristics are identified to enumerate all admissible spring configurations with a minimum number of springs. Spring configurations for the statically balanced articulated manipulators with up to four degrees of freedom are obtained and illustrated schematically. An index function for the evaluation of the robustness of such a statically balanced articulated manipulator with respect to each spring configuration is also proposed.

Design of a Gravity-Balanced General Spatial Serial-Type Manipulator

A novel methodology for the design of a gravity-balanced serial-type spatial manipulator is presented. In the design, gravity effects of the system can be completely compensated at any configuration. The gravity balance of the n-DOF manipulator is achieved by the suspensions of only n zero-free-length springs, where each spring is individually fitted between a primary link and its adjacent auxiliary link. No spring has to be installed across the spatial manipulator from a far remote link to ground such that the motion interference among the springs and the links can be prevented. Besides, since the embedded auxiliary links along the primary links of the manipulator form a series of spatial parallelogram revolute-spherical-spherical-revolute modules, the active DOFs of the system remain the same as the primary manipulator and the range of motion of the manipulator will not be hindered. As a result, the n-DOF manipulator can serve the general function of an articulated serial-type manipulator in kinematics. The simulated results of a 6DOF gravity-balanced manipulator modeled on ADAMS shows that the static equilibrium as well as the kinematics of the system can be successfully accomplished by this proposed methodology. DOI: 10.1115/1.4001816

Design of Perfectly Static-Balanced One-DOF Planar Linkage With Revolute Joint Only

A systematic methodology for the design of a statically balanced, single degree-of-freedom planar linkage is presented. This design methodology is based on the concept of conservation of potential energy, formulated by the use of complex number notations as link vectors of the linkage. By incorporating the loop closure equations, the gravitational potential energy of the system can be simplified as the function of the vectors of all ground-adjacent links. The balance of the gravitational potential energy of the system is then accomplished by the elastic potential energy of a zero free-length spring on each ground-adjacent link of the linkage. As a result, spring constants and installation configurations of the ground-attached springs are obtained. Since the variation of the gravitational potential energy of the linkage at all configurations can be fully compensated by that of the elastic potential energy of springs, this methodology provides an exact solution for the design of a general spring balancing mechanism without auxiliary parallel links. Illustrations of the methodology are successfully demonstrated by the spring balancing designs of a general Stephenson-III type six-bar linkage and a Watt-I type six-bar linkage with parallel motion.Copyright

On the Operation Space and Motion Compatibility of Variable Topology Mechanisms

With the implementation of just one mechanism, variable topology mechanisms can serve the functions of many mechanisms by changing their topology. These types of mechanisms have raised interest and attracted numerous studies in recent years, yet few of these studies have focused discussing of these mechanisms in light of their operation space. As the change of a variable topology mechanism is induced by either intrinsic constraints or constraints due to the change of joint geometry profile, the operation space of kinematic joints and kinematic chains in various working stages is changed in accordance. A theoretic framework based on the concept of the operation space of variable topology mechanisms is presented here. A number of characteristics with regard to the motion compatibility among joints and loops in different working stages are derived, laying a foundation for systematical synthesis of variable topology mechanisms. Design of a novel latch mechanism for the standardized mechanical interface system is given as an illustrative example for the synthesis of a variable topology mechanism.

Gravity Balancing of a Spatial Articulated Manipulator Based on a New Spring Mechanism

Based on the theory of conservation of potential energy, design of a gravity-balancing spatial articulated manipulator by the use of a proposed spring mechanism is presented. Since the gravitational potential energy of the mass system of a spatial articulated manipulator of n links depends only on the orientation of each link within the system, the entire manipulator can then be considered to be equivalent to an array of n degenerated ground-adjacent links in the aspect of the potential energy. Moreover, since the gravitational potential energy of a rotary link moving in a vertical plane is a trigonometric function and the Scotch york mechanism is also a well-known harmonic motion generator, a new spring mechanism composed of a Scotch york, a compression spring, and a gear pair is used to balance the gravitational potential energy of each degenerated link. With a built-in spring mechanism embedded on each joint of the articulated manipulator, the entire spatial articulated manipulator maintains can be in equilibrium at all configurations, which is verified by the simulation of the system modeled in a commercial software Pro-Engineer. The prototyping of a practical system will be implemented in the near future.Copyright

On the Topological Representation and Compatibility of Variable Topology Mechanisms

Variable topology mechanisms can serve many design functions with only one mechanism through changing their topology, these mechanisms have raised broad interest and attracted many studies in recent years, yet few have consolidated the different types of these mechanisms, nor discussed them in the light of the space they operate in. This work classified the variable topology mechanisms, and presented an expression of the mechanism’s working space. Variable topology mechanisms are classified into three types, topology changed by intrinsic constraints, topology changed by joint geometry change, and topology changed by external constraints. The causes and effects of various constraints inducing a topology change are described with the operating space, compatibility characteristics of joints, loops, and working stages with the operating space are established, verifying whether joints will constraint and lock up each other. The admissible operating space for a loop interface pairs so that loops are compatible, and the requisites of different working stages being workable with each other are identified. As a result, some basic requirements for admissible variable topology mechanisms are unveiled, laying a foundation stone for systematical synthesis of variable topology mechanisms.Copyright

On the Design of the Gravity Balancer Using Scotch Yoke Derivative Mechanism

Design of the gravity balancer prototypes based on the modified Scotch yoke type spring mechanism is presented. Followed by the brief description of the conceptual design and validation of the method, design of a one degree-of-freedom (dof) rotary system is proposed. In the 1st generation prototype model, the spring-gravity system is designed as a whole, while, in the 2nd generation model, the gravity balancer is designed as a modular unit for easy adjustment and simple replacement. The friction force due to the prismatic joints of a Scotch yoke derivative mechanism for the latter model has been greatly reduced by using a bushing bearing along with a guidance pole. As a consequence, by showing the equilibrium of the rotary system being sensitive to the fine-tuned position of the end-effector payload, the 2nd prototype model successfully demonstrates the gravity balancing capability of the entire system at all configurations within its range of motion. The issues related to the design of the one-dof gravity balancer are discussed, and the potential use of such balancers in the multiple-dof system is also proposed.

Design of the Deployable Mechanisms Based on the Cardanic Motion of Planar Four-Bar Linkage

A deployable mechanism is a mechanism that is designed to be repeatedly expanded and contracted without failure. Most deployable mechanisms are over-constrained mechanisms with a mobility of one. Although many deployable mechanisms had been proposed and employed in application in the past decades, few generalized methodologies for the synthesis of both planar and spatial deployable mechanisms are available. In this paper, a systematic methodology, based on the Cardanic motion of planar linkage, for the synthesis of both the spatial and planar deployable mechanisms is presented. By using the characteristics that some of the coupler points of Cardanic linkages are able to move along a straight line, a building unit mechanism that utilizes such a linkage can be extended or retracted as desired. Once the boundary conditions of the building unit mechanisms are obtained, design of an entire deployable mechanism, planar or spatial, can be fulfilled. After the design is achieved, motion of the synthesized mechanism is simulated in Pro/Engineer, and the prototype of a planar model is manufactured for the justification of this method.Copyright

Kinematic Modeling and Kinesiology Study of a Human Index Finger Based on a Tendon-Driven Articulated Manipulator With Disc-Cam Pulleys

A tendon-driven articulated manipulator with disc-cam pulleys is presented for the kinematic modeling and the motion analysis of a human index finger. Using the proposed model as a foundation, the driving forces of the tendons of human finger could be further evaluated and compared with the estimation from the EMG signals. The motivation of using such a tendon-driven articulated manipulator model to emulate the structure and functionality of a human finger is initiated by the similarities between these two systems, where the joint motions of the systems are both activated by the force transmission of tendons either by the base-driven actuators or the contraction of human muscles. However, the distinction between these two systems is that the extension/flexion motion of a human finger is coupled with the abduction/adduction motion due to the anatomical complexity of the expansion hood of a human finger, while the motion of a general articulated manipulator is not coupled. Moreover, since the shapes of the base and head of phalanges are irregular, the joints of a human finger cannot be simply treated as a perfect revolute joint. Hence, for the motion compatibility between the human finger and the articulated manipulator, the functionality of the expansion hood and the tendon system of a human index finger are identified and the joints are treated as revolute joints with non-circular pulleys. Based on the kinematic model and motion simulation of the finger-alike tendon-driven articulated manipulator is accomplished, and the prototyping model of the manipulator is constructed. Motion comparison between the models with the constant and non-constant moment arms is also implemented.Copyright

Design of an Orthosis for the Weight Balance of Human Lower Limbs

Most existing lower limb orthosis use actuators and active controller to guide the motion of human lower limbs. Actuators with relatively large power are usually required to compensate the gravity effect of the human lower limbs, even for a normal walking. Hence, design of an orthosis for the weight balance of human lower limbs is desired. For the motion compatibility, the human hip joint is treated as a planar pair and the knee joint as a revolute pair. As a consequence, while the lower limb is in motion, the exact positions of the mass centers of the human lower limbs cannot be obtained. Hence, in this work, topological synthesis of the orthosis mechanisms, which can trace the mass centers of the human thigh and shank, respectively, is implemented. The weight balance of the human lower limbs is achieved by fitting a minimum number of zero-free-length springs. Based on the anthropometric parameters, dimensions of the lower limb orthosis is determined and the proposed design is justified by the simulation executed by the software of ProEngineer. Finally, a first generation prototype is built.Copyright