The serial link manipulators are most commonly used for industrial applications. The positional accuracy is an important specification for performance evaluation of a serial chain manipulator. The factors influencing the positional accuracy of serial link robotic manipulator includes joint clearances, and drive backlash. This paper presents method for evaluating the effect of joint error on positional accuracy of the robotic manipulator. Serial chain Two Revolute Joint (2R) planar manipulator is modeled to position the end effector in workspace. The inverse kinematic analysis under ideal joint provides the link properties for respective end effector location. Formulation for manipulator link properties under influence of the joint clearance is presented. Effect of drive backlash on positional accuracy of end effector is analyzed. Positional deviations at end effector positions over workspace are estimated. Maximum error under influence of backlash and clearances is estimated at all possible end effector positions.

Closed chain mechanisms are used as robotic manipulators with special features. A planar two-DOF closed loop mechanism provides desired position of an end effecter in a confined workspace with two input motions. Position of end effecter depends on various factors including joint clearance. Positional accuracy forms important parameter for kinematic analysis of mechanism. This paper presents simple approach for quantifying error due to joint clearance in a two-DOF mechanism. Generalized scheme for positional deviation with and without clearance at joint is presented. Orientation of clearance links for maximum positional error is identified. Error at various positions is quantified in relation with clearance link length. Computer programming is used as a tool to workout positional analysis of mechanism. Results show that error is independent of magnitude of clearance, however, a function of location of end effecter in workspace.

Ovality is a main defect in all pipe bending techniques. An objective of the work is to control ovality in pipe bending. A new concept is suggested for reducing the flattening or ovality. Based on the concept, a mechanism is developed for bending pipes. This mechanism has provisions for precompression of the pipe along the directrix of maximum deformation during bending. Experimentation is carried out on this mechanism and dimensions are measured at 13 discrete places along the length of the pipe. Percentage ovality is computed using experimental results. It is justified by using equations of radius and displacement functions. Minimization of potential energy by sequential search method is done. The methodical approach is presented in this paper. Results show that precompression reduces ovality of the pipe after bending.

Straight pipes with a circular cross section are processed into smooth bends by various pipe bending techniques. After bending, the initial circular cross section is deformed with thickness change. These changes from ideal are normally referred to as “ovality” and “thinning.” Their influence on the subsequent behavior of curved pipes is not yet fully understood. The aim of this paper is to present a factual method to reduce thinning of the wall thickness of pipe during bending. A new mechanism is developed for bending of pipes. This mechanism has a provision of precompression (radial squeeze) of the pipe along the directrix of maximum deformation during bending. This is achieved by clamping the pipe using two parallel plates from top and bottom. In fact, the pipe is wrapped using two rollers—one from inside and one from outside in the horizontal plane—and two plates parallel to the horizontal plane—one from the top and one from the bottom. Experimentation is carried out on this mechanism, and thicknesses are measured at the grid points along the length of the pipe. From the experimental values of thicknesses on the tension and compression sides, dimensionless variations in wall thickness of various groups of pipes are computed for different precompression values. In order to represent the thickness at any point, a mathematical equation is derived. Analytical values of thickness variations on tension and compression sides are computed using this equation. Experimental and analytical results are compared, and its methodical approach is presented in this paper. Results show that precompression reduces thickness variation of the pipe after bending.

The results of fracture toughness of the glass/carbon fibre reinforced epoxy hybrid composites, as expressed by K IC and G IC —the critical stress intensity factor and the critical strain energy release rate respectively, in the crack opening mode—are presented in the following paper. The tests have been conducted in the 3-point bending configuration for the specimens having a total reinforcement content of about 55%. The K IC has been evaluated from the G IC and also from the standard expressions normally used for isotropic materials. Similarly, the G IC and K IC have been evaluated by using both P max , the maximum load, and P Q , the point of intersection on the load displacement curve with a line having 5% less slope than the slope of the curve at the origin. The trend of the results obtained by these two methods is considerably different particularly with increasing glass content in the hybrids. The values of G IC and K IC obtained from P Q exhibit a distinct positive hybrid effect. The hybrids having both the glass and carbon fibres not only have values better than those expected by the rule of mixtures but also better than those of the composite reinforced entirely by glass or carbon fibres.