3,817 research outputs found
SPRK: A Low-Cost Stewart Platform For Motion Study In Surgical Robotics
To simulate body organ motion due to breathing, heart beats, or peristaltic
movements, we designed a low-cost, miniaturized SPRK (Stewart Platform Research
Kit) to translate and rotate phantom tissue. This platform is 20cm x 20cm x
10cm to fit in the workspace of a da Vinci Research Kit (DVRK) surgical robot
and costs $250, two orders of magnitude less than a commercial Stewart
platform. The platform has a range of motion of +/- 1.27 cm in translation
along x, y, and z directions and has motion modes for sinusoidal motion and
breathing-inspired motion. Modular platform mounts were also designed for
pattern cutting and debridement experiments. The platform's positional
controller has a time-constant of 0.2 seconds and the root-mean-square error is
1.22 mm, 1.07 mm, and 0.20 mm in x, y, and z directions respectively. All the
details, CAD models, and control software for the platform is available at
github.com/BerkeleyAutomation/sprk
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
Appropriate Design of Parallel Manipulators
International audienceAlthough parallel structures have found a niche market in many applications such as machine tools, telescope positioning or food packaging, they are not as successful as expected. The main reason of this relative lack of success is that the study and hardware of parallel structures have clearly not reached the same level of completeness than the one of serial structures. Among the main issues that have to be addressed, the design problem is crucial. Indeed, the performances that can be expected from a parallel robot are heavily dependent upon the choice of the mechanical structure and even more from its dimensioning. In this chapter, we show that classical design methodologies are not appropriate for such closed-loop mechanism and examine what alternatives are possible
Joint-space adaptive control of a 6 DOF end-effector with closed-kinematic chain mechanism
The development is presented for a joint-space adaptive scheme that controls the joint position of a six-degree-of-freedom (DOF) robot end-effector performing fine and precise motion within a very limited workspace. The end-effector was built to study autonomous assembly of NASA hardware in space. The design of the adaptive controller is based on the concept of model reference adaptive control (MRAC) and Lyapunov direct method. In the development, it is assumed that the end-effector performs slowly varying motion. Computer simulation is performed to investigate the performance of the developed control scheme on position control of the end-effector. Simulation results manifest that the adaptive control scheme provides excellent tracking of several test paths
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