Static Calibration of the DLR Medical Robot MIRO, a Flexible Lightweight Robot with Integrated Torque Sensors

This paper presents a method to calibrate the model of serial and flexible lightweight robots with joint sided torque sensors in the assembled state. The calibration is done in an iterative three-step process, based on static robot poses. In the first step the kinematics and stiffnesses of the flexible components are calibrated. Second the models of the integrated torque sensors are identified in a linear least square solution. In the third step the masses, the centers of gravity and the torque sensor offsets are estimated using linear regression. The calibration steps are repeated stepwise to account for their dependencies. The calibration procedure is simulated and experimentally performed with the medical lightweight robot MIRO of the German Aerospace Center. Through the iterative procedure the pose accuracy improves from about 5mm translational error and 2.5 ° rotational error to 1mm and 0.3 ° regarding the entire workspace

Design and validation of a system for controlling a robot for 3D ultrasound scanning of the lower limbs

Peripheral arterial disease (PAD) is a common circulatory problem featured by arterial narrowing or stenosis, usually in the lower limbs (i.e. legs). Without sufficient blood supply, in the case of PAD, the patient may suffer from intermittent claudication, or even require an amputation. Due to the PAD’s high prevalence yet low public awareness in the early stages, its diagnosis becomes very important. Among the most common medical imaging technologies in PAD diagnosis, the ultrasound probe has the advantages of lower cost and non-radiation. Traditional ultrasound scanning is conducted by sonographers and it causes musculoskeletal disorders in the operators. In addition, the data obtained from the manual operation are unable for the three-dimensional reconstruction of the artery needed for further study. Medical ultrasound robots release sonographers from routine lifting strain and provide accurate data for three-dimensional reconstruction. However, most existing medical ultrasound robots are designed for other purposes, and are unsuited to PAD diagnosis in the lower limbs. In this study, we present a novel medical ultrasound robot designed for PAD diagnosis in the lower limbs. The robot platform and the system setup are illustrated. Its forward and inverse kinematic models are solved by decomposing a complex parallel robot into several simple assemblies. Singularity issues and workspace are also discussed. Robots need to meet certain accuracy requirements to perform dedicated tasks. Our robot is calibrated by direct measurement with a laser tracker. The calibration method used is easy to implement without requiring knowledge of advanced calibration or heavy computation. The calibration result shows that, as an early prototype, the robot has noticeable errors in manufacturing and assembling. The implemented calibration method greatly improves the robot's accuracy. A force control design is essential when the robot needs to interact with an object/environment. Variable admittance controllers are implemented to adapt the variable stiffness encountered in human-robot interaction. An intuitive implementation of the passivity theory is proposed to ensure that the admittance model possesses a passivity property. Finally, experiments involving human interaction demonstrate the effectiveness of the proposed control design