Analysis and compensation control of passive rotation on a 6-DOF electrically driven Stewart platform

With the development of motor control technology, the electrically driven Stewart platform (EDSP), equipped with a ball screw or lead screw, is being widely used as a motion simulator, end effector, and vibration isolator. The motor drives the lead screw on each driven branch chain to realize 6-DOF motion of the moving platform. The control loop of the EDSP adopts the rotor position as a feedback signal from the encoder or resolver on the motor. When the moving platform of the EDSP performs translational or rotational motion, the lead screw on each driven branch chain passively generates a relative rotation between its screw and nut in addition to its original sliding motion. This type of passive rotation (PR) of the lead screw does not disturb the motor; hence, it cannot be detected by the position sensor attached to the corresponding motor. Thus, the driven branch chains cause unexpected length changes because of PR. As a result, the PR generates posture errors on the moving platform during operation. In our research, the PR on the EDSP was modeled and analyzed according to the geometry configuration of EDSP. Then, a control method to compensate for the posture errors caused by the PR was proposed. Finally, the effectiveness of the analysis process and compensation control method were validated; the improvement in pose accuracy was confirmed both by simulation and experiments.

Research on boundary slip of hydrostatic lead screw under different driving modes

The flow state of oil film in the hydrostatic lead screw directly affects the transmission performance of the screw pair. The static and dynamic characteristics of a new type of double driven hydrostatic screw-nut pair (DDHSNP) are studied under different motion modes. The boundary condition of navier slip model is introduced into the lubricating mathematical model of DDHSNP, and the influences of boundary slip on the axial bearing capacity, axial stiffness and damping coefficient in micro scale are researched by finite difference method. The results show that when the motor runs at high speed (the rotating speed range of the screw and nut driven motor is 1000–9000 rpm), the existence of boundary slip leads to a improvement of the axial bearing capacity and stiffness coefficient of DDHSNP in the case of single-drive operation and dual-drive differential feed (the range of rotation difference is 10–100 rpm), which is more obvious under the single-drive mode. The increase rate of stiffness coefficient induced by boundary slip is much larger than that of bearing capacity. In addition, the boundary slip has little effect on the damping coefficient of DDHSNP in either single drive operation or dual drive differential operation.

Optimization of the drive mechanism with lead screw using Isight software

The ball screws are characterized with better positioning accuracy and higher efficiency and load ratings than the same size lead screw, but still cannot fully replace their functionality mostly due to the self-locking. Leads screws are recommended especially for such applications as grippers, lifters, presses and vertical positioning drives. By proper selection of the lead screw geometrical features and application of the modern materials, it is possible to obtain much more advantageous parameters of the drive system. In this paper, the methodology of optimization of the drive mechanism with lead screw using Isight software is presented. The performed sensitivity analysis allowed not only to find the influence of various constructional features such as: size of the thread, length of the screw and material properties, on the maximum load capacity of the drive mechanism and its inertia, but also determine its scale impact. The obtained results can improve the design process of lead screw mechanism.

Modeling and Analysis for the Transmission Characteristics of a Proposed Dual-Drive Hydrostatic Lead-Screw System

This paper proposes a novel dual-drive hydrostatic lead-screw system (DDHLS). The design enables a lower feed speed and a better transmission performance than the conventional hydrostatic lead screw (HLS). Considering the nut-misalignment, the lubricating mathematical model of the DDHLS is established based on the perturbation method and solved by the finite difference method. The influences of the nut-radial-displacement, the nut-tilt, and the dual-drivable design on the transmission performance of the DDHLS are researched. The results show the nut-misalignment can regularly reduce or increase the axial load capacity, the axial stiffness coefficient, and the axial damping coefficient. Significantly, the dual-drivable design can improve the axial load capacity and the axial stiffness coefficient while hardly affects the axial damping coefficient.

Design and Fabrication of Wheelchair into Foldable Bed

In this paper lead screw mechanism is used to convert a wheelchair into bed and vice versa. When lead screw mechanism is operated, the foot rest which is downward goes till the level of seat of wheelchair and simultaneously the back support goes down to the same level making, its stretcher and vice versa, when it is converted into wheelchair from stretcher. Below the seat, a defecation system has been provided which is detachable and is operated by sliding mechanism. It is designed and fabricated in such a way that it can be used in hospitals as well as for personal use at home. Below the seat, a defecation system has been provided which is detachable and is operated by sliding mechanism. Also, obstacle avoiding sensor i.e., ultrasonic sensor is used to know if any obstacle will come in front of wheelchair, siren bell will ring. Keywords: Fabrication, Hospital, Mobility Aid, Lead Screw, Design, Wiper Motor, Wheelchair, Battery

A Study of Parameters that Effect to Width of Chocolate Line Based on Additive Manufacturing and Screw Based Extrusion

This paper presents a study of parameters that effect to width of chocolate line based on additive manufacturing and screw based extrusion. In order control a width of chocolate extruded lines for constructing chocolate model, three pitch of lead screw, three distances between nozzle and workspace, and three extrusion rates are assigned as independent variables. The result was showed that those three independent parameters were affects to width of extruded chocolate line. When the pitch of lead screw and the chocolate extrusion rate were increased, the width of the chocolate width had been expended. Moreover, if the distances between nozzle and workspace was increase, the chocolate width had been narrow.