Philip A. Voglewede

On the connections between cable-driven robots, parallel manipulators and grasping

Although cable-driven robots and parallel manipulators have very similar architecture, the presence of the unidirectional constraints in cable-driven robots makes it impossible to apply many of the concepts and methods used for parallel manipulators. Instead many tools from grasping are more suitable, since fingers also provide unidirectional constraints. This article reviews some of the connections, provides some basic definitions that we hope leads to standardized terminology for cable-driven robots, and finally transfers the antipodal grasping theorem to planar cable-driven robots.

Overarching framework for measuring closeness to singularities of parallel manipulators

Singular configurations where a parallel manipulator can lose stiffness are well documented and studied in literature. There exist many proposed measures on how close a pose is to these singularities. This paper develops a framework which unites many of the existing measures, provides further understanding for others, and creates new ones. The framework originates from a physical understanding of singularities with a natural progression to a constrained optimization problem. The solution to the optimization problem is a simple general eigenvalue problem of constant matrices. The power of this new framework is that it is easy to compare existing measures and develop new ones. Several examples of measures within the framework are given.

Dynamic Performance of a SCARA Robot Manipulator With Uncertainty Using Polynomial Chaos Theory

This short paper outlines how polynomial chaos theory (PCT) can be utilized for manipulator dynamic analysis and controller design in a 4-DOF selective compliance assembly robot-arm-type manipulator with variation in both the link masses and payload. It includes a simple linear control algorithm into the formulation to show the capability of the PCT framework.

Application of the antipodal grasp theorem to cable-driven robots

Cable-driven robots and multifinger grasps are closely related to each other by the fact that both systems can provide unidirectional forces to the object to be constrained. While prior research primarily related cable-driven robots to grasps without friction, this article seeks to establish relationships between certain cable-driven robots and grasps with friction. Those relationships are used to transfer the antipodal grasp theorem to cable-driven robots, resulting in the so-called antipodal cable theorem. A planar and spatial version are presented.

Application of Workspace Generation Techniques to Determine the Unconstrained Motion of Parallel Manipulators

Due to clearances in their passive joints, parallel manipulators always exhibit some unconstrained motion at the end effector. The amount of unconstrained motion depends on the pose of the manipulator and can increase significantly at or near singular configurations. This paper shows precisely how much unconstrained end effector motion exists at the end effector for a large class of parallel manipulators, namely those with passive revolute and/or spherical joints, if all the joint clearances are known. This includes the planar 3RRR, and, in approximation the Gough-Stewart and the Hexa manipulators. For the analysis, the passive joints are assumed to be revolute or spherical because these are the simplest cases. However the general framework also applies to other joint types, although leading to more complex calculations. For most manipulators, determining the amount of end effector motion can be transformed to a workspace generation problem. Therefore, general workspace generation techniques can be utilized.

Design of an Active Ankle-Foot Prosthesis Utilizing a Four-Bar Mechanism

This article discusses the design and testing of a powered ankle prosthesis. This new prosthesis mimics nonamputee (normal) ankle moments during the stance phase of gait through the use of an optimized spring loaded four-bar mechanism. A prototype prosthesis based on the optimization was designed, fabricated, and tested. The experimental results achieved 93.3% of the simulated theoretical ankle moment giving substantial evidence that this approach is a viable in designing powered ankle prostheses.

Mechanical Vibration Inhibits Osteoclast Formation by Reducing DC-STAMP Receptor Expression in Osteoclast Precursor Cells

It is well known that physical inactivity leads to loss of muscle mass, but it also causes bone loss. Mechanistically, osteoclastogenesis and bone resorption have recently been shown to be regulated by vibration. However, the underlying mechanism behind the inhibition of osteoclast formation is yet unknown. Therefore, we investigated whether mechanical vibration of osteoclast precursor cells affects osteoclast formation by the involvement of fusion-related molecules such as dendritic cell-specific transmembrane protein (DC-STAMP) and P2X7 receptor (P2X7R). RAW264.7 (a murine osteoclastic-like cell line) cells were treated with 20ng/ml receptor activator of NF-κB ligand (RANKL). For 3 consecutive days, the cells were subjected to 1h of mechanical vibration with 20μm displacement at a frequency of 4Hz and compared to the control cells that were treated under the same condition but without the vibration. After 5days of culture, osteoclast formation was determined. Gene expression of DC-STAMP and P2X7R by RAW264.7 cells was determined after 1h of mechanical vibration, while protein production of the DC-STAMP was determined after 6h of postincubation after vibration. As a result, mechanical vibration of RAW264.7 cells inhibited the formation of osteoclasts. Vibration down-regulated DC-STAMP gene expression by 1.6-fold in the presence of RANKL and by 1.4-fold in the absence of RANKL. Additionally, DC-STAMP protein production was also down-regulated by 1.4-fold in the presence of RANKL and by 1.2-fold in the absence of RANKL in RAW264.7 cells in response to mechanical vibration. However, vibration did not affect P2X7R gene expression. Mouse anti-DC-STAMP antibody inhibited osteoclast formation in the absence of vibration. Our results suggest that mechanical vibration of osteoclast precursor cells reduces DC-STAMP expression in osteoclast precursor cells leading to the inhibition of osteoclast formation.

Mechanism State Matrices for Planar Reconfigurable Mechanisms

This paper improves augmented mechanism state matrices by replacing joint code with screw system notation. The proposed substitution allows for a more specific description of the joints in the mechanism and the capability to describe both spatial and planar mechanisms. Examples are provided which elucidate the proposed approach.Copyright

Multidisciplinary Engineering Systems Graduate Education: Master of Engineering in Mechatronics

Abstract - The masters graduate degree program in engineering must change to respond to the needs of the modern practicing engineer. What is needed is a balance between theory and practice, between academic rigor and the best practices of industry, presented in an integrated way that feeds the needs of modern practicing engineers and the companies they work for. The new Master of Engineering in Mechatronics program attempts to remedy these deficiencies. The key element is the one-credit module which: balances theory and practice where concepts are application-driven, not theory-driven; identifies and understands industrial best practices by dissecting them into engineering and mathematical fundamental models; achieves innovation by assembling these fundamental models into new products and processes; analyzes both existing and new products and processes using computer simulations within a topic area; demonstrates hardware to show system realization and validity of modeling and analysis results; shows videos of industry systems and interviews with industry experts; discusses best practices to achieve sustainability of products; and maintains flexibility through 15 one-hour blocks of instruction - a 5-week mini-course or longer if preferred.

Controller Implementation of a Powered Transtibial Prosthetic Device

A new type of powered transtibial prosthesis was designed and fabricated. This device has reasonable size, weight and strength for daily use. In order to test the device on human subjects, a control algorithm and a control system are required. A two level control algorithm, which includes a higher level finite state controller and lower level PID controllers, is proposed and the configuration of this system is presented in this paper. An absolute encoder, a current sensor and two sets of force-sensing resistors are used to provide the feedback; a dSPACE system and MATLAB Simulink are used to realize the higher level control, and a DC motor controller is used to realize the lower level PID controller.Copyright