Development of a high-performance force display for material science

Force display systems are important in virtual reality and other applications. While conventional force displays are active systems with actuators and as such may become inherently dangerous, passive force displays are effective methods for assuring safety. In this paper, we developed a brake using electrorheological (ER) fluid, and showed a passive force display system using ER brakes with two degrees of freedom. We also discuss basic control experiments of the system.

We have developed a high performance force display system with a parallel manipulator. The manipulator is composed of a parallel mechanism with direct drive linear servo actuators. The mechanism is called a fixed linear type parallel mechanism. Since the actuators are fixed on the base, the high speed motion of the manipulator is possible. In addition, the mechanism has high load capacity and back derivability. These characteristics lead to a high performance force feedback control. We describe the design policy, the analysis of the operation area, the prototyping and control of the parallel manipulator.

We developed ER actuators with high performance. An ER actuator consists of ER clutch, reduction gear unit and electric motor. The electrodes of the output-shaft side in the developed ER actuators are made of light material such as CFRP, and the moment of inertia of the ER actuators with respect to the output-shaft becomes very small. As a result, the large torque/inertia ratio can be obtained, compared with conventional actuators. When comparing with powder clutches in which the torque/inertia ratio is considered to be extremely high, the torque/inertia ratio of small-size ER actuators is not inferior. Considering the slow response property of powders in powder clutches, it can be stated that ER actuators are devices with extremely high response characteristics. Firstly we discuss the design and structure of ER actuators. Secondly the experimental results are presented. Then, the control experiments are executed. The developed ER actuators are used in order to develop the new force display system which has high-fidelity force-presentation ability.

Development of a fiber daylighting system based on the parallel mechanism and direct focus detection

Despite improvements in cancer survival rates, metastatic and surgery‐resistant cancers, such as pancreatic cancer, remain challenging, with poor prognoses and limited treatment options. Enhancing drug bioavailability in tumors, while minimizing off‐target effects, is crucial. Metal–organic frameworks (MOFs) have emerged as promising drug delivery vehicles owing to their high loading capacity, biocompatibility, and functional tunability. However, the vast chemical diversity of MOFs complicates the rational design of biocompatible materials. This study employed machine learning and molecular simulations to identify MOFs suitable for encapsulating gemcitabine, paclitaxel, and SN‐38, and identified PCN‐222 as an optimal candidate. Following drug loading, MOF formulations are improved for colloidal stability and biocompatibility. In vitro studies on pancreatic cancer cell lines have shown high biocompatibility, cellular internalization, and delayed drug release. Long‐term stability tests demonstrated a consistent performance over 12 months. In vivo studies in pancreatic tumor‐bearing mice revealed that paclitaxel‐loaded PCN‐222, particularly with a hydrogel for local administration, significantly reduced metastatic spread and tumor growth compared to the free drug. These findings underscore the potential of PCN‐222 as an effective drug delivery system for the treatment of hard‐to‐treat cancers.

Experimental research on lubrication and vibration characteristics of water-lubricated stern bearing for underwater vehicles under extreme working conditions

In this paper we present a parallel robot with flexure hinges for target alignment system of a high power laser facility. The robot contains a parallel mechanism with 6 DOF which has nanometer positioning accuracy and is driven by six linear actuators. We design a new flexure hinge which has higher accuracy, strong environmental suitability and simple structure compared with conventional flexure hinge which has backlash and friction issues. The kinematics analysis of the parallel mechanism is also discussed. The simulation analysis of the mechanism is done by ADAMS. The mechanism is proved meeting the design requirements by comparing the results of the theory analysis and the simulations.

In this paper we present a redundantly actuated parallel mechanism for ankle rehabilitation. The proposed device has the advantage of mechanical and kinematic simplicity when compared with the state-of-the-art multi-degree-of-freedom parallel mechanism prototypes while at the same time it is fully capable of carrying out the exercises required by the ankle rehabilitation protocols. Optimization of the device workspace, dexterity, torque output and size was carried out during the design phase of the device. The development of the system involved the realization of a new customized linear actuator able to meet the speed and force requirements of the device functionality. We also discuss the impedance-based control scheme used for the redundantly actuated device, which allows the execution of both assistive and resistive strengthening rehabilitation regimes. Results from the control of a single linear actuator and further experimental tests including the position tracking of the fully actuated platform are presented. It is believed that the performance and the simplicity of the proposed mechanism will allow the widespread use of the system as a new aid tool for ankle rehabilitation.

This paper provides an overview of the embedded joint-space control approach developed for THOR, a new series elastic humanoid. The 60 kg robot features electromechanical linear series elastic actuators (SEAs), enabling low-impedance control of each joint in the lower body via linear to rotary and parallel mechanisms. We present a distributed joint impedance control framework that leverages a custom dual-axis motor controller to track position, velocity, and torque setpoints for each pair of joints. The required actuator forces are tracked using an inner force control loop combining feedforward and PID control with a model-based disturbance observer (DOB). Unlike previous approaches, we utilize an inverse plant model based on the open-loop actuator dynamics to simplify tuning of the cascaded controller by decoupling DOB estimates from the inner loop gains. The effectiveness of the proposed approach is verified through trajectory tracking and dynamic walking experiments conducted on the THOR humanoid utilizing a complementary optimization-based whole-body controller.

Parallel mechanism is composed of a platform connected to a fixed base by some linear actuators called struts. The kinematic chains of parallel mechanism are driven by these actuators to its base and has high stiffness and low weight so it can realize high speed and accurate positioning ability. The Stewart platform is one of the parallel mechanism. In serial mechanism, the direct kinematics solution is easy, but the inverse kinematics solution is very involved. The other way, in the parallel mechanism the inverse kinematics solution is easy but the direct kinematics solution is very involved. In this paper, a new method named “origami solution” to solve the direct kinematics solution of Stewart platform is proposed and some basic equations in “origami solution” are conducted. This method is based on the “Geneqc.c” which is a computer program to get roots of general equations. In the last, the method is evaluated by some examples of the Stewart platform. The direct kinematics solution is solved in 0.01mm accuracy in about 1 second calculation time by 32 bit computer.

Due to the wave, it is dangerous for the crew to transfer from ship to port and offshore platform. Accordingly, some large vessel are equipped a movement reduction device using parallellink mechanism. However, they are too big and expensive to put on the smaller ship such as pleasure cruiser. In this paper, we derive the model of the under-actuated parallel link mechanism for the motion reduction device. For simplicity, planner closed-link with 4 rotational joints and 2 linear actuators is considered. Then a controller is designed for each case with and without gravity.

This paper deals with a multiple mobile working robot, which has a six-legged locomotion function and a vertically articulated manipulator. The walking mechanism consists of a parallel link mechanism connecting two frames with three linear actuators and six extendable legs fixed to the frames. The manipulation function has 4 degrees of freedom and locomotion function has 6 degrees of freedom, thus this working robot is a redundant mechanism with 10 degrees of freedom. We propose a trajectory following control method by switching the normalizing matrix according to the freedom. The simulation results and the experimental results leads to the availability of the method.

Hollow multishelled structures (HoMSs) have distinguished advantages, such as a large effective surface area, an optimized mass transport route, and a high loading capacity, but the fabrication of HoMSs has been a big challenge. In 2009, we developed a universal and facile method for HoMS fabrication, i.e., the sequential templating approach (STA). Progress in the synthetic methodology has enabled the study of HoMSs to develop and has made it a research hotspot in materials science. To date, HoMSs have shown their advantages in a wide range of applications, including catalysis, energy conversion and storage, drug delivery, etc. Based on the understanding in this field, we recently revealed the unique temporal–spatial ordering properties of HoMSs. Furthermore, we have been wondering if the structure of a HoMS can be modulated at the molecular level. Encouragingly, metal–organic frameworks (MOFs) are star materials with clearly defined molecular structures. The compositions, geometries, functionalities and topologies of MOFs have been well tuned by rational design. Integrating the unique properties of MOFs and HoMS could realize the systemic design of materials from the molecular to the micro-level, which would provide a series of advantages for various applications, such as developing high performance catalysts for cascade and/or selective catalysis, combining the reaction and separation process for multiple reactions, releasing drugs in a certain environment for smart medicine, and so on. We believe it is time to summarize the recent progress in the integration of MOFs and HoMSs, including HoMSs coated with MOFs, MOF-derived HoMSs, and MOFs with a hollow multishelled structure, and we also put forward our personal outlook in relation to the future opportunities and challenges in this emerging yet promising research field.

Force-closure workspace analysis of cable-driven parallel mechanisms

Most advanced manufacturing processes require precise linear-position control for material transfer, packaging, assembly, and electrical wiring. To achieve precise linear motion, most of these high-performance manufacturing machines use X-Y sliding tables with permanent-magnet rotary motors and rotary-to-linear couplers. Though this method is the most widely used, it has disadvantages of low accuracy, complex mechanical adjustments, high cost, and low reliability. This paper describes the use of the variable-reluctance-driving principle to construct a novel linear direct-drive actuator system for high-performance position control in manufacturing automation. The proposed actuator has a very simple structure and it can be manufactured easily. There is no need for magnets and no limitation on the traveling distance. The actuator is extremely robust and can be used in hostile environment. A novel control method, using cascade control and the force-linearization technique, is developed and implemented for precision position control of the actuator. Experimental results of the motion system indicate that the system has fast responses with good accuracy.