Tuning of Parameters for Robotic Contouring Based on the Evaluation of Force Deviation

The application of industrial robots with advanced sensor systems in unstructured environments is continuously becoming wider. A widely used type of advanced sensor systems is the force-torque sensor. Force-torque sensors are typically used for applications such as robot grinding, sanding, polishing, and deburring, where a constant force is exerted upon a workpiece. In this research, control parameters for exerting a constant force along a predefined path are evaluated in laboratory conditions. The experimental setup with the contouring force feedback is composed of a Fanuc LRMate six-degree-of-freedom industrial robot with an integrated force-torque sensor. Control parameters of the Contouring function within the Fanuc robot controller are tuned in four contouring experiments. The experiments conducted in this research are: i) flat beam, ii) flat beam with a rigid support, iii) wave shaped compliant plate, and iv) compliant flat plate. During the experiments, contouring parameters were altered in order to collect the feedback on the values of the force to be used for the evaluation of the force deviation. A fitness function for the evaluation of the force deviation and the tuning of the control parameters is presented. The fitness function enables a selection of initial control parameters which minimize the force deviation during the robot contouring process

Improved Instrumented Compliant Wrist Design

Interaction between robot and environment is an extremely important aspect of robotic research. Compliance helps reduce the impact effects of robot/environment interaction. Hybrid position/force control is important in most robotic tasks; accurate position control is needed in unconstrained directions, and accurate force control is needed in constrained directions. Force control can be more responsive with a compliant force/torque sensor, but positional accuracy is reduced with compliance. An instrumented compliant wrist device can be used to achieve both responsive force control and accurate position control. The wrist is connect in series between the end of the robot and the tool, and is designed to partially surround the tool, thus reducing the distance between the end of the robot and the end of the tool. The wrist device uses rubber elements for compliance and damping, and a serial linkage, with potentiometers at each joint, is used for sensing the deflections produced in the wrist. This document describes the newest version of the instrumented compliant wrist, including modifications and improvements to the wrist described in Design of a Tool Surrounding compliant Instrumented Wrist , available as tech report MS-CIS-91-30, GRASP LAB 258 from the University of Pennsylvania. Changes include a more protective sensing linkage structure and improved electronics. The compliance, kinematics, and accuracy of the wrist are presented. Also, software for determining the wrist transform, and plans for the wrist are given

Design of a Tool-Surrounding Compliant Instrumented Wrist

Interaction between robot and environment is an extremely important aspect of robotic research. Compliance helps reduce the effects of impact when there is robot/environment interaction. To accomplish useful tasks, it is important to implement hybrid control; accurate position control is needed in unconstrained directions and accurate force control is needed in constrained direction. Force control can be more responsive with a compliant force/torque sensor [3], but positional accuracy is reduced with compliance. An instrumented compliant wrist device can be used to achieve both responsive force control and accurate position control. The wrist is connected in series between the end of the robot and the tool. The wrist device uses rubber elements for compliance and damping, and a serial linkage, with potentiometers at each joint, is used for sensing the defections produced in the wrist. Several major improvements are proposed for the Xu wrist. The wrist can be designed to surround the tool, thus reducing the distance between the end of the robot and the end of the tool, thus reducing the distance between the end of the robot and the end of the tool. The compliant structure is redesigned for more even compliance, and the sensing structure kinematics are simplified. In this over, the compliance, kinematics, and accuracy of the wrist will be presented. Also, software for finding the wrist transform, and plans for the wrist are given

Body Lift and Drag for a Legged Millirobot in Compliant Beam Environment

Much current study of legged locomotion has rightly focused on foot traction forces, including on granular media. Future legged millirobots will need to go through terrain, such as brush or other vegetation, where the body contact forces significantly affect locomotion. In this work, a (previously developed) low-cost 6-axis force/torque sensing shell is used to measure the interaction forces between a hexapedal millirobot and a set of compliant beams, which act as a surrogate for a densely cluttered environment. Experiments with a VelociRoACH robotic platform are used to measure lift and drag forces on the tactile shell, where negative lift forces can increase traction, even while drag forces increase. The drag energy and specific resistance required to pass through dense terrains can be measured. Furthermore, some contact between the robot and the compliant beams can lower specific resistance of locomotion. For small, light-weight legged robots in the beam environment, the body motion depends on both leg-ground and body-beam forces. A shell-shape which reduces drag but increases negative lift, such as the half-ellipsoid used, is suggested to be advantageous for robot locomotion in this type of environment.Comment: First three authors contributed equally. Accepted to ICRA 201

Analysis and experimental evaluation of a Stewart platform-based force/torque sensor

The kinematic analysis and experimentation of a force/torque sensor whose design is based on the mechanism of the Stewart Platform are discussed. Besides being used for measurement of forces/torques, the sensor also serves as a compliant platform which provides passive compliance during a robotic assembly task. It consists of two platforms, the upper compliant platform (UCP) and the lower compliant platform (LCP), coupled together through six spring-loaded pistons whose length variations are measured by six linear voltage differential transformers (LVDT) mounted along the pistons. Solutions to the forward and inverse kinematics of the force sensor are derived. Based on the known spring constant and the piston length changes, forces/torques applied to the LCP gripper are computed using vector algebra. Results of experiments conducted to evaluate the sensing capability of the force sensor are reported and discussed