Design and analysis of a novel active screw-drive pipe robot

This study proposes a novel active screw-drive in-pipe robot that can adapt the circular-type and square-type pipe structure. The pipe robot is composed of four driving units and a wall-pressing suspension mechanism. Each driving unit contains a motor, a transmission train, and an electromagnetic brake, which is for switching the motion transmission route. DC motors drive the helical wheels, and the incline angle of the helical wheels can be adjusted by using the electromagnetic brake. The wheels of the driving unit exhibit rolling and steering motion. Thus, the robot is capable of translation movements, rotation movements, and screw motions with respect to the axis of the pipe according to the different positions of the helical wheels. The robot can avoid obstacles by using the rotation and screw modes. Moreover, the wall-pressing mechanism is analyzed and modified, and a criteria for entering a reduction pipe reducer are derived for the double scissor-like suspension mechanism. We also analyze the robot motion in curved pipes in two typical postures. The simulation experiments reveal the relationship between the translation and rotation motion of the robot and indicates that the steering angle of the wheels can be regarded as a regulator to adjust the movement speed of the robot aside from tuning the posture of the robot. Elbow experiments are conducted to verify the effectiveness of the motion strategy. The robot can be adapted for both circular and square tube pipes without any change in its structure due to the special configuration.

Design and analysis of a tendon-based computed tomography–compatible robot with remote center of motion for lung biopsy

Nowadays, biopsy is a decisive method of lung cancer diagnosis, whereas lung biopsy is time-consuming, complex and inaccurate. So a computed tomography–compatible robot for rapid and precise lung biopsy is developed in this article. According to the actual operation process, the robot is divided into two modules: 4-degree-of-freedom position module for location of puncture point is appropriate for patient’s almost all positions and 3-degree-of-freedom tendon-based orientation module with remote center of motion is compact and computed tomography–compatible to orientate and insert needle automatically inside computed tomography bore. The workspace of the robot surrounds patient’s thorax, and the needle tip forms a cone under patient’s skin. A new error model of the robot based on screw theory is proposed in view of structure error and actuation error, which are regarded as screw motions. Simulation is carried out to verify the precision of the error model contrasted with compensation via inverse kinematics. The results of insertion experiment on specific phantom prove the feasibility of the robot with mean error of 1.373 mm in laboratory environment, which is accurate enough to replace manual operation.

Axodes Analysis of the Multi DOF Parallel Mechanisms and Parasitic Motion

The general motion of a spatial mechanism is a screw motion about an instantaneous screw axis (ISA). The locus of a series of ISAs will form a ruled surface, which can be called as an axode. For a spatial mechanism with only one degree of freedom (DOF), the ISAs or the axodes of the moving platform are unique. However, the axodes of the parallel mechanisms (PMs) with multi DOF are related to the specific motion which has various possibilities. In this paper, the ISAs of the multi DOF PMs are studied using the jacobian matrix which is changing with the configurations of the moving platform. The axodes of the multi DOF PMs with different inputs or outputs are obtained using this method. Based on the analyzed results, it is very clear that the general motions of the PMs are screw motions or rotations about a series of ISAs. In the end, the parasitic motion of the PMs is studied. For a PM, the parasitic motion will exist if the rotational freedoms are not rotations about a fixed point or axis.

Four Motion Branches of an Origami Based Eight Bar Spatial Mechanism

An eight bar spatial mechanism inspired from an origami paper fold by considering the carton panels as links and creases as revolute joints is proposed. The constraint deposition and motion characteristics analyses of the eight bar spatial mechanism show that the mechanism implements one screw motion and one pure translation. The configuration space of the mechanism comprises four subspaces. Through adding different geometrical constraints to the eight bar spatial mechanism, different motions of the end-effector are limited leading to three 2-DOF and one 1-DOF motion branches. Additional geometrical constrained conditions in four motion branches with aimed motions of double translations, single translation and two single screw motions are revealed. In the first two motion branches, the eight bar spatial mechanism remains the constant relative orientations of joint-axes. However, the joint-axes of the eight bar spatial mechanism change their orientations in the last two motion branches. Kinematic analyses are discussed in four motion branches, respectively.

Analysis Method of Screw Algebra for Motion Characteristics of a 4-URU Parallel Metamorphic Mechanism

A new 4-URU parallel metamorphic mechanism is proposed. A new method using screw adjacency matrix to describe the structural transformation of metamorphic mechanisms is put forward. This method overcomes the limitations of existing topological description method which cannot analyze the metamorphic mechanisms spatial structures and motion characteristics. Then the screw algebra method for analyzing the metamorphic mechanisms motion characteristics is introduced in detail. Firstly, screw motions homogeneous system of linear equations is determined by the screw adjacency matrix. Then the equations basic solution system determines the anti-screw system. Finally calculate the moving platforms motion screw system. Thus the metamorphic mechanisms motion characteristics, such as spatial structure in different configurations, the number of components and joints, degrees of freedom are obtained.

HELICOIDAL MINIMAL SURFACES IN ℍ2×ℝ

It is shown that a minimal surface in ℍ2×ℝ is invariant under a one-parameter group of screw motions if and only if it lies in the associate family of helicoids. It is also shown that the conjugate surfaces of the parabolic and hyperbolic helicoids in ℍ2×ℝ are certain types of catenoids.