Search

A new method for the design of hybrid position/force controllers for constrained manipulators is derived. This method can be applied to all types of constraint due to contact with the environmcnt; including constraint due to contact at the end effector, constraint due to more than one robot manipulating a workpiece, and constraint due to the bracing of a robot arm against a work surface. The manipulator and its contact with the environment are modeled in terms of lower order pairs. From this model a general equation describing the constraint on the motion of the arm is derived. The task is modeled as a set of essential position vectors and a set of essential force vectors. A hybrid position/force controller is derived to control the position and force at the joints of a manipulator such that the motion of the the robot conforms to the constraints imposed on it due to contact with the environment; and the motion at the end effector, and the force at the contact with the environment are those required for the performance of the task. The method is illustrated by a simple three degree of freedom example.

Emulating on Earth the weightlessness of a manipulator floating in space requires knowledge of the manipulator's mass properties. A method for calculating these properties by measuring the reaction forces and moments at the base of the manipulator is described. A manipulator is mounted on a six-degree-of-freedom sensor, and the reaction forces and moments at its base are measured for different positions of the links of the manipulator as well as for different orientations of its base. A procedure is developed to calculate from these measurements some combinations of the mass properties of the manipulator. The mass properties identified are not sufficiently complete for computed torque and other dynamic control techniques, but do allow compensation for the gravitational load on the links of the manipulator, and for simulation of weightless conditions on a space emulator. The algorithm has been experimentally demonstrated on a PUMA 260 and used to measure the independent combinations of the sixteen mass parameters of the base and three proximal links of the manipulator. >

Programming by human demonstration is an intuitive method of robot programming, in which the programmer demonstrates how a task is performed using a human/robot teaching device that measures human motion, and the data gathered is used to generate the robot program. A direct duplication of the demonstrated trajectory would result in unnecessary robot motion due to human "wiggles" and unintended motion. To identify a more satisfactory robot trajectory, a method is presented that uses multiple demonstrations of the same task. Variation in human trajectories between trials is attributed to human inconsistency and is used to define an obstacle free region, by applying the Jordan curve theorem. The shortest path within the obstacle free region is determined, resulting in a shorter robot path than any of the demonstrations. Thus the presence of human inconsistency is used to improve robot performance. The analysis is restricted to planar translational motion. >

The mechanical engineering design curriculum of one university (MIT) is outlined. The sophomore level Introduction to Design course and the senior level Design Projects course are described in more detail, and compared and criticized. The challenge of design education is ascribed to two sources: (a) the reach of design development that is expected of the students, and (b) the difficulty of providing adequate feedback to the students. It is proposed that (i) the limitations on the science based undergraduate curriculum for providing a professional education in design be formally recognized, and that there be a clearer understanding of what a graduating engineer is expected to be capable of, and what is to be provided by graduate school and/or company based on-the-job training programs; (ii) that established principles of design be taught at appropriate stages in the undergraduate curriculum to the extent that they match the students’ design development and experience; and (iii) that undergraduate design courses incorporate projects in which students’ designs are manifested in hardware to provide an effective complement to the feedback provided by the faculty teaching the course.

A computer graphics based advisory system has been developed to aid in the design and manufacture of submarine hulls. The design and manufacture advisor incorporates models of the materials (steel) and processes (bump forming roll bending. welding and fixturing) used for the manufacture of the hulls and allows the user to explore the effect of different material qualities (described in terms of variances of thickness and yield strength) and different manufacturing parameters (punch penetration punch spacing and number of fixtures for example) on the resulting quality (circuliuity) of the hull section. By Designing through Manufacture in this way the resulting design of the submarine hull section is not just a geometric representation of the desired shape of the hull but incorporates explicit information about the materials and processes used to create the shape and of the quality that results from the designer!5 choice of materials and processes.

Assessment feedback from teachers gains consistently low satisfaction scores in national surveys of student satisfaction, with concern surrounding its timeliness, quality and effectiveness. Equally, there has been heightened interest in the responsibility of learners in engaging with feedback and how student assessment literacy might be increased. We present results from a five year longitudinal mixed methods enquiry, thematically analysing semi-structured interviews and focus groups with undergraduate students who have experienced dialogic feed-forward on a course in a British university. We use inferential statistics to compare performance pre- and post-assessment intervention. The assessment consisted of submitting a draft coursework essay, which was discussed and evaluated face-to-face with the course teacher before a self-reflective piece was written about the assessment process and a final essay was submitted for summative grading. We evidence that this process asserted a positive influence on the student learning experience in a number of inter-related cognitive and affective ways, impacting positively upon learning behaviour, supporting student achievement and raising student satisfaction with feedback. We advocate a cyclic and iterative approach to dialogic feed-forward, which facilitates learners’ longitudinal development. Programme teams should offer systematic opportunities across curricula for students to understand the rationale for and develop feedback literacy.