Optimization and Control of a Planar Three Degrees of Freedom Manipulator with Cable Actuation

The paper analyzes a planar three degrees of freedom manipulator with cable actuation. Such a system can be understood as a special type of hybrid parallel kinematic mechanism composed of the rigid serial chain and the additional auxiliary cable system. The advantage of the auxiliary cable mechanism is the ability to reconfigure the whole system. The fulfillment of sufficient prestressing is the constraint of the optimization process. Computed Torque Control with a cable force distribution algorithm is implemented. The control algorithm performance is examined on different trajectories, including non-smooth motion requests, and its robustness is tested by randomly generated errors of the model parameters in regulators. The results demonstrate that the optimized structure is capable of controlling the manipulator motion and keeping the cable prestressing within the given limits.

Kinematics Analysis of Incomplete Gear and Rack Pumping Unit

A pumping unit with incomplete gear and rack reversal was designed for smooth motion and low energy consumption. This paper first describes the working principle of the pumping unit. The kinematical equation of the pumping unit is established on the basis of analyzing the kinematic relationship between the first tooth meshing area, the normal meshing area and the final tooth meshing area of incomplete gear and rack. The kinematic relationship curve of the pumping unit is obtained by ADAMS simulation. The simulation results show that the theoretical model is correct. By comparing the results with the conventional pumping unit, it can be seen that: the pumping unit has a smooth movement of the up-down strokes, with fluctuations of movement only in the process of changing directions. The incomplete gear and rack drive is smooth, which can improve the kinestate of the pumping unit.

Dynamic Modelling and Motion Control of a 4-DOF SCARA Robotic Arm for Various Farm Applications

Agriculture as a key industry for human food suply will face various concerns in near future. This research is complementary and aims to present the dynamic modelling and simulation, as well as algorithm development of a 4-DOF SCARA-type robotic arm designed for real agricultural cultivation process, such as seeding, watering, fertilizing, weeding, etc. In terms of a previously designed system, the equations of motion profile were solved (acceleration and deceleration control of joints) to reduce inertia, ensure a smooth motion, and minimize torque requirement. The algorithm is evaluated by PTP motion, TCP linear motion, and spline motion. The results show that the developed algorithm can move the TCP using ST-profile. Furthermore, it can control all joints for an estimated time duration. A novel method was developed to manoeuvre the TCP along the shortest path to reach a goal point. Finally, the algorithm was evaluated in a closed path inside the working space.

High-resolution light field prints by nanoscale 3D printing

A light field print (LFP) displays three-dimensional (3D) information to the naked-eye observer under ambient white light illumination. Changing perspectives of a 3D image are seen by the observer from varying angles. However, LFPs appear pixelated due to limited resolution and misalignment between their lenses and colour pixels. A promising solution to create high-resolution LFPs is through the use of advanced nanofabrication techniques. Here, we use two-photon polymerization lithography as a one-step nanoscale 3D printer to directly fabricate LFPs out of transparent resin. This approach produces simultaneously high spatial resolution (29–45 µm) and high angular resolution (~1.6°) images with smooth motion parallax across 15 × 15 views. Notably, the smallest colour pixel consists of only a single nanopillar (~300 nm diameter). Our LFP signifies a step towards hyper-realistic 3D images that can be applied in print media and security tags for high-value goods.

A 4-DOF SCARA Robotic Arm for Various Farm Applications: Designing, Kinematic Modelling, and Parameterization

The agriculture industry has faced various challenges nowadays. This research is the first part of a project that presents the designing process, kinematic modelling, and parameterization of a 4-DOF SCARA-type robotic arm specifically designed for work in an agricultural field in terms of seeding, watering, fertilizing, weeding, harvesting, and transporting. The designing of parameters, such as optimum degrees of freedom and component configuration, was done. The kinematic model was calculated using the Denavit-Hartenberg method. The structure of robot was developed for inertia reduction, smooth motion, and torque minimization. The results show that the working space, maximum front access, and side access of developed robotic arm were 11.4 m2, 2.9 m, and 2.4 m, respectively. The results indicate that the robot has sufficient surface coverage for defined farm work.

Optimisation of a Polarisation Nephelometer

An analysis of the influence caused by polarization nephelometer parameters on the scattering matrix measurement accuracy in a non-isotropic medium is presented. The approximation errors in the actual scattering volume and radiation beam by an elementary scattering volume and an elementary radiation beam are considered. A formula for calculating the nephelometer base is proposed. It is shown that requirements to an irradiation source of a polarizing nephelometer, i.e. mono-chromaticity and high radiation intensity and directivity in a wide spectral range can be satisfied by a set of high brightness LEDs with a radiating (self-luminous) small size body. A 5-wavelength monochromatic irradiation source, with an emission flux of (0.15–0.6) W required for a polarization nephelometer, is described. The design of small-sized polarizing phase control units is shown. An electronic circuit of a radiator control unit based on an AVR-Atmega 8-bit microcontroller with feedback and drive control realized by means of an incremental angular motion sensor and a software PID controller is presented. Precise and smooth motion of the radiator is ensured by standard servo-driven numerical control mathematics and the use of precision gears. The system allows both autonomous adjustment of the radiator’s reference positions and adjustment by means of commands from a personal computer. Both the computer and microcontroller programs were developed with the use of free software, making it possible to transfer the programs to Windows‑7(10), Linux and embedded Linux operating systems. Communication between the radiator’s position control system and the personal computer is realised by means of a standard noise immune USB-RS485 interface.

Identification of Non-Transversal Motion Bifurcations of Linkages

The local analysis is an established approach to the study of singularities and mobility of linkages. The key result of such analyses is a local picture of the finite motion through a configuration. This reveals the finite mobility at that point and the tangents to smooth motion curves. It does, however, not immediately allow to distinguish between motion branches that do not intersect transversally (which is a rather uncommon situation that has only recently been discussed in the literature). The mathematical framework for such a local analysis is the kinematic tangent cone. It is shown in this paper that the constructive definition of the kinematic tangent cone already involves all information necessary to distinguish different motion branches. A computational method is derived by amending the algorithmic framework reported in previous publications.

Hydrostatic pressure prevents chondrocyte differentiation through heterochromatin remodeling

Articular cartilage protects and lubricates joints for smooth motion and transmission of loads. Due to its high water content, chondrocytes within the cartilage are exposed to high levels of hydrostatic pressure, which has been shown to promote chondrocyte identity though unknown mechanisms. Here we investigate the effects of hydrostatic pressure on chondrocyte state and behavior, and discover that application of hydrostatic pressure promotes chondrocyte quiescence and prevents maturation towards the hypertrophic state. Mechanistically, hydrostatic pressure reduces H3K9me3-marked constitutive heterochromatin and concomitantly increases H3K27me3-marked facultative heterochromatin. Reduced H3K9me3 attenuates expression of pre-hypertrophic genes, replication, and transcription thereby reducing replicative stress. Conversely, promoting replicative stress by inhibition of topoisomerase II decreases Sox9 expression, suggesting that it enhances chondrocyte maturation. Our results reveal how hydrostatic pressure triggers chromatin remodeling to impact cell fate and function.