DETC2005-84349 HYBRID TARGET TRACKING MANIPULATION THEORIES FOR COMBINED FORCE AND POSITION CONTROL IN OPEN AND CLOSED LOOP MANIPULATORS

ABSTRACT This paper presents a new manipulation theory for controlling compliant motions of a robotic manipulator. In previous closed loop control methods, both direct kinematics and inverse kinematics of a manipulator must be resolved to convert feedback force and position data from Cartesian space to joint space. However, in many cases, the solution of direct kinematics in a parallel manipulator or the solution of inverse kinematics in a serial manipulator is not easily available. In this study, the force and position data are packed into one set of "motion feedback," by replacing the force errors with virtual motion quantities, or one set of "force feedback," by replacing motion errors with virtual force quantities. The joint torques are adjusted based on this combined feed back package. Since only Jacobian of direct kinematics or Jacobian of inverse kinematics is used in the control scheme, the computational complexity is reduced significantly. The applications of this theory are demonstrated in simulation experiments with both serial and parallel manipulators. KEYWORDS Target tracking, open loop, closed loop, manipulation, hybrid control INTRODUCTION In many applications such as deburring, grinding, scribing and contour following, a manipulator is required to follow a predefined position trajectory in the tangent direction of a surface while maintaining a contact force in the normal direction. These tasks need appropriate control of motion and force. In the beginning, a typical force control strategy was used to command an actuator torque. This strategy combined feedback of force with feedback of position (and velocity) and corrected the error through a common controlle

Computational kinematics of general Stewart platform

This dissertation addresses the kinematics, redundancy resolution and control methods for Stewart platform and algorithms for mechanism design and optimization. ^ In this dissertation, techniques are developed to support Jacobian analysis and position analysis for kinematics of Stewart platform. Especially, a numerical method for finding all the solutions of the forward position analysis problem for the most general Stewart platform is presented. This method is based on the polynomial continuation method. However, it constructs start system and the homotopy based on physical design rather than mathematical equations. It has superior efficiency since it eliminates all of the extraneous paths before the solution tracking procedure starts. This method is further generalized as a Continuous Design Transmutation Method for solving problems in engineering analysis and design, which involve searching solutions of a system of polynomial equations. ^ To overcome deficiencies of Stewart platform, redundancy schema are suggested in this work. The kinematic constraint equations and system Jacobian for redundant Stewart platform are developed. The global optimal resolutions of joint rates are formulated and solved as a problem of the calculus of variations. The results show that significant improvement can be achieved by introducing and optimizing the redundant DOF. ^ A new manipulation method for controlling compliant motion of a Stewart platform is presented. In this work, the force and position variables are packed into one set of motion feedback by replacing the force errors with virtual motion quantities. The joint inputs are adjusted based on this combined feed back package. Since only the Jacobian of inverse kinematics is used in the control scheme, the computational complexity is reduced. The applications of this method are demonstrated in simulation experiments. ^ At last, a formulation and numerical method for design and optimization of the profile of cutting blades is presented. It is shown that the front line curvature of a cutting blade is related with the cutting force and input force or torque in the form of a first-order differential equation. The mechanics in the cutting process can be improved by adjusting the curvature of the rotary blade according to the solution of the differential equation.

Combining Three Mapping Strategies to Reveal Quantitative Trait Loci and Candidate Genes for Maize Ear Length

Ear length (EL) is an important trait in maize ( L.) because it is positively correlated with grain yield. To understand the genetic basis of natural EL variation, a F, a four-way cross and a genome-wide association study (GWAS) population were used to identify the quantitative trait loci (QTLs) and candidate EL genes. Linkage mapping identified 14 QTLs in two types of populations from multiple environments. Six of them were located in three common genomic regions considered “stable QTLs”. Candidate genes for the three stable QTLs were identified by the GWAS results. These were related to auxin transport, cell proliferation, and developmental regulation. These results confirm that maize EL is under strong genetic control by many small-effect genes. They also improve our understanding of the genetic basis of maize EL