DESIGN AND KINEMATICS ANALYSIS OF MECHANICAL ARM OF TRIMMER

The development of mechanization has greatly liberated the labour force, promoted socialized mass production, and created infinite social wealth. Its influence is significant and far-reaching, and agricultural production has undergone revolutionary changes. Aiming at the problems of poor working environment, high labour intensity and low working efficiency of manual pruning, a mechanical arm of branch pruning machine was designed, which realized the three-dimensional layered cylindrical pruning of individual tree. In this paper, a five-degree-of-freedom trimmer manipulator is designed, which is mainly composed of base, big arm, small arm, wrist and finger blade. The motion equation of the mechanism is established by using the Denavit–Hartenberg parameter (D-H parameter) method, and the corresponding motion curve is fitted by using MATLAB software. The components of the trimmer arm are designed virtually by using 3D modeling software, and assembled into a complete trimmer arm. The assembly drawing is imported into the simulation analysis software ADAMS for kinematics simulation. The results show that the speed-time pattern has obvious positive and negative changes at 3s, which proves that this stage is the hand cutting stage of jujube pruning; The acceleration time graph is gentle in the whole movement, and the curve approaches to a straight line, which proves that the movement of the mechanical arm of the jujube pruning machine is stable in the pruning process. Through the analysis of the simulation curve, it provides a theoretical basis for the research of the mechanical arm of the trimmer.

Positioning Performance of a Sub-Arc-Second Micro-Drive Rotary System

In the macro/micro dual-drive rotary system, the micro-drive system compensates for the position error of the macro-drive system. To realize the sub-arc-second (i.e., level of 1″–0.1″) positioning of the macro/micro dual-drive rotary system, it is necessary to study the positioning performance of the sub-arc-second micro-drive rotary system. In this paper, we designed a sub-arc-second micro-drive rotary system consisting of a PZT (piezoelectric actuator) and a micro rotary mechanism, and used simulation and experimental methods to study the positioning performance of the system. First, the micro-drive rotary system was developed to provide ultra-precise rotary motion. In this system, the PZT has ultrahigh resolution at a level of 0.1 nanometers in linear motion; a micro rotating mechanism was designed according to the composite motion principle of the flexible hinge, which could transform the linear motion of piezoelectric ceramics into rotating motion accurately. Second, the drive performance was analyzed based on the drive performance experiment. Third, kinematics, simulation, and experiments were carried out to analyze the transformation performance of the system. Finally, the positioning performance equation of the system was established based on the two performance equations, and the maximum rotary displacements and positioning error of the system were calculated. The study results showed that the system can provide precision motion at the sub-arc-second and good linearity of motion. This study has a certain reference value in ultra-precision positioning and micromachining for research on rotary motion systems at the sub-arc-second level.

A Barycenter Control Method for the Bioinspired Forest Chassis Robot on Slope

To improve the stability of forestry chassis on the slope, a chassis-installed barycenter adjustable mechanism (BAM) is designed, and the control method of the counterweight is proposed to make the chassis barycenter move suitably to achieve the design purpose. The kinematic analysis of BAM is carried out, and the relationship between the translation, rotation, and vertical displacement of counterweight and the chassis barycenter is calculated. Furthermore, the variation curves obtained in Matlab show the barycenter can translate 100 mm, rotate from 0 to 360 degrees, and lower about 180 mm in the vertical direction. Adams is adopted to complete the kinematics simulation of the chassis, indicating that the control method can effectively adjust the barycenter position. Finally, experiments are carried out under slope conditions to analyze chassis stability by testing plantar pressure. The results show that forest chassis using the barycenter control method helps keep stable on the slope of 15 degrees, much better than standard normal chassis.

Design, Simulation and Verification of a 7-DOF Joint Motion Simulation Platform

The human body has many joints, and joint injuries frequently occur in various sports. To explore the biomechanical state of ligaments or muscles in human joints before and after damage, and to help doctors judge the damage and repair of joints, this article proposes a seven-degree-of-freedom platform based on three rotations spherical parallel mechanism for simulating human joint motion. Taking the knee joint as an example, this article simplified its model, and performed kinematics simulation by ADAMS to verify the feasibility of this mechanism. And based on the TRIO motion controller, we established the physical testing system. The correctness is finally verified by experiment in kind, which proves the feasibility of the joint motion simulation platform. And in terms of accuracy, it also performances very well. For example, when it needs to rotate 30∘ around the Y-axis, its actual rotation angle is 29.6∘, the error is less than 2%, and its translation error is also within 3%.

Novel Surface Design of Deployable Reflector Antenna Based on Polar Scissor Structures

Space-deployable mechanisms can be used as supporting structures for large-diameter antennas in space engineering. This study proposes a novel method for constructing the surface design of space reflector antennas based on polar scissor units. The concurrency and deployability equations of the space scissor unit with definite surface constraints are derived using the rod and vector methods. Constraint equations of the spatial transformation for space n-edge polar scissor units are summarized. A new closed-loop deployable structure, called the polar scissor deployable antenna (PSDA), is designed by combining planar polar scissor units with spatial polar scissor units. The over-constrained problem is solved by releasing the curve constraint that locates at the end-point of the planar scissor mechanism. Kinematics simulation and error analysis are performed. The results show that the PSDA can effectively fit the paraboloid of revolution. Finally, deployment experiments verify the validity and feasibility of the proposed design method, which provides a new idea for the construction of large space-reflector antennas.