Narrow clearance peg-in-hole assembly is a typical industrial assembly scene. Due to the motion accuracy limitation of industrial robot system and the uncertainty of the assembly circumstance, robotic autonomous assembly of narrow clearance peg in hole assisted by machine vision and force feedback has always been a research focus in this field. However, few studies focused on accomplishing it in a short time while maintaining minimal forces. On the other hand, in some extreme scenarios, such as nuclear, camera lenses may age quickly when exposed to high-dose radiation, requiring a non-visual peg-in-hole method. In this article, aiming at peg-in-hole assembly tasks without vision, and inspired by wrist force sense of human, a robotic narrow clearance peg-in-hole location and insertion methods with wrist force sensation are proposed. The collaborative robot obtains the accurate location of the hole by touching the hole edge several times, named “force-sense-based location”. And then, the peg is automatically inserted into the hole by the collaborative robot with four basic motions named “approach”, “slippage”, “rolling” and “drilling”. A geometric theoretical model was deduced to guarantee the feasibility of the developed method. To avoid excessive contact force, all four motions were designed with admittance hybrid/position control in different directions. The experimental results demonstrate the effectiveness of the proposed method, while the key factors affecting their performance were analyzed. Finally, we compared the methods with three peg-in-hole methods and comprehensively analyzed their performances in terms of assembly time, assembly force, and sensitivity to initial bias. This article provides a new effective method for automatic assembly of narrow clearance peg-in-hole tasks.Note to Practitioners—The efficiency of product assembly has significantly increased thanks to the emergence of robotics. Robots are progressively taking the role of humans in many manual assembly procedures. Peg-in-hole assembly is a common assembly activity accounting for about 40% of the total assembly work. The majority of peg-in-hole assembly techniques start by locating the holes visually, then make modifications based on high-frequency force input. However, vision is frequently prohibited in many real-world assembly scenarios, such as those that actually happen in the dark, low light, or radiation. This paper proposed the use of a UR5e collaborative robot mounted with a six-dimensional force/torque (FT) sensor to complete the peg-in-hole assembly task. The collaborative robots are excellent for applications requiring frequent interactions such as peg-in-hole assembly for high security and great price-performance ratio. A robotic peg-in-hole locating algorithm based on touch sense is presented. This method does not require the assistance of visual equipment like cameras or laser-type displacement transducer. Instead, the location and contact force of the component in various contacts are used to estimate the part’s positional information. The presented method can locate different rigid cylindrical parts and performs fairly precise positioning. The algorithm’s tolerance for position error uncertainty allows it to handle chamfered peg-in-hole assemblies with a narrow clearance ($25\sim 90\mu $m). The mathematical derivation ensures the reliability and adaptability of the assembly approach. But a limitation of this approach is that it can only presently be used for cylindrical peg-in-hole assembly with flat end faces. In the future, to expand the application of our method, we will carry out theoretical derivation, control strategy design for more parts with typical shapes, as well as the placement and insertion task of irregular parts.

This work proposed surgical forceps as a sensor that integrated step-coated Fiber Bragg Grating (FBG) for the 3-axial force sensing in the percutaneous spinal endoscopic robot. The step-coated FBG achieved a reflection spectrum with double wavelength peaks, providing more wavelength signals for fault-tolerant decoupling. The temperature and force sensitivity were regulated by adjusting the coating size to reduce decoupling error to 3.68% F.S, solving the span temperature (≥ 20 °C) disturbance from the operating room to the operative area. The optical fiber metallization and laser welding package was proposed to achieve stable connections between the quartz optical fiber and metal forceps. The innovative package made the forceps tolerate 180 °C dry-heat sterilization and aqueous erosion, allowing for sterilized reuse (11 times with error lower than 4.98% F.S) and long-term stability (one month with error lower than 4.36% F.S). A Wavelet Fuzzy Entropy (WFE) and Extreme Learning Machine (ELM) based dynamic fault-tolerant decoupling strategy was proposed. The WFE-ELM reduced the sensor error to 4.42% F.S. under the influence of spectrum chirp noise and single-branch FBG breakage, and the fault-tolerant recovery rate within 10% F.S. error was raised to 40.23%. The designed surgical instruments were integrated with a spinal endoscopic surgical robot to conduct the spine model and pig experiments, verifying its force-sensing effectiveness.

Six-axis force/moment (6-A F/M) sensors make surgical robots effectively sense intraoperative force feedback and drilling status information, reducing the operating challenges and psychological burden of doctors, which also improves the quality and safety of surgery. However, it is difficult for current commercial electrical 6-A F/M sensors to adapt the electromagnetic environment in the operating room, and status changes after installation can also reduce accuracy. At the same time, there is a strong vibration coupling of low-frequency force information, leading to low identification accuracy and slow response speed in the drilling and milling status. Aiming at these problems, an elliptical torus-based 6-A fiber optic F/M sensor and its in-situ calibration method for orthopedic surgical robot force sensing are proposed. Furthermore, combined with the multichannel one-dimensional convolutional gated recurrent unit (M1-DCGRU), a fast and accurate identification of seven drilling stages was realized. The final force sensing error is less than 7.1%, and the drilling state identification accuracy is at least 93.9%. The designed sensor has higher accuracy, is compatible with magnetic resonance imaging (MRI), and accurately identifies finer drilling stages without relying on other sensors.

Disassembly is a core procedure in remanufacturing. Disassembly is currently carried out mainly by human operators. It is important to reduce the labor content of disassembly through automation, to make remanufacturing more economically attractive. Threaded fastener removal is one of the most difficult disassembly tasks to be fully automated. This article presents a new method developed for automating the unfastening of screws. An electric nutrunner spindle with a geared offset adapter was fitted to the end of a collaborative robot. The position of a hexagonal headed screw in a fitted stage was known only approximately, and its orientation in the hole was unknown. The robot was programed to perform a spiral search motion to engage the tool onto the screw. A control strategy combining torque and position monitoring with active compliance was implemented. An existing robot cell was modified and utilized to demonstrate the concept and to assess the feasibility of the solution using a turbocharger as a disassembly case study. Note to Practitioners-Remanufacturing is known to generate substantial economic, social, and environmental benefits. Disassembly is the first operation in a remanufacturing process chain. Unfastening threaded parts (“unscrewing”) is a common disassembly task accounting for approximately 40% of all disassembly activity. Like other disassembly tasks, often, unscrewing has to be carried out manually in remanufacturing due to difficulties caused by the variable and unpredictable condition of the end-of-life (EoL) products to be remanufactured. Automating unscrewing operations should reduce the labor content of disassembly, thus lowering remanufacturing costs and promoting the adoption of remanufacturing. This article proposes the use of a collaborative robot to perform autonomous unfastening of hexagonal headed screws. Collaborative robots have built-in force sensors and can be programed to carry out operations involving not only position but also active force and compliance control. They can work safely alongside human operators, enabling the latter to focus on jobs requiring high cognitive or manipulation abilities. The article presents a novel spiral search technique developed to improve the rate of successful engagement between the robot end effector and the screw heads despite uncertainties in the location of the screws. The technique was successfully demonstrated on the dismantling of a turbocharger but can readily be applied to other EoL products with hexagonal headed screws. It can also be used with other kinds of screws (e.g., Phillips screws and slotted-head screws) simply by changing the tool and tuning the robot control parameters. A limitation of the proposed technique is that it can only deal reliably with undamaged screws. In our future research, we will consider screws that are in imperfect conditions through usage and develop appropriate solutions for their removal by robots.

The purpose of this research is to present a new method to achieve precise position tracking control for robot finger with variable stiffness mechanism. First, the variable stiffness design of the finger which is actuated by SMA-3 fibers is presented. Then, the relationship between the variation of pulling force ΔF of the bending robot finger and input voltage of SMA-3 is established. In addition, the relationship between the pulling force F and the input voltage of SMA-2 wire is established as well. Therefore, a control method based on these models for the position tracking of robot finger with variable stiffness characteristics is proposed. The experimental results show that the proposed method has better performance than traditional PID control when the stiffness changed by heating current, resulting in a reduction of maximum error by 86%.

The chained form system is a controllable nonholonomic system, wherein the motion planning and control had been often researched. Therefore, based on the chained form transformation, the motion planning and control of nonholonomic system can be researched by the motion planning and control of chained form system. According to this thought, motion planning and control of nonholonomic multi-joint manipulator were researched in this paper. A method of nonholonomic motion planning and control was proposed by the chained form transformation, and validity of the method was proved by computer simulation

A wheeled mobile robot with trailers has been studied as a class of nonholonomic systems. It is proved that a system of a tractor and trailers with an appropriate connecting mechanism can be stabilized to desired positions via nonholonomic motion control. Trailers, on the other hand, have been developed and widely used in the industry. The main focus of industrial design is set on reducing tracking error from a reference trajectory. This paper attempts to bridge over the gap between these two approaches. We develop a design theory of trailer systems with passive steering. The designed systems show a good performance in practical path following, and accept the chained form transformation and nonlinear control strategies for nonholonomic systems.

A wheeled mobile robot with trailers has been studied as a class of nonholonomic systems. It is proved that a system of a tractor and trailers with an appropriate connecting mechanism can be stabilized to desired positions via nonholonomic motion control. Trailers, on the other hand, have been developed and widely used in the industry. The main focus of industrial design is set on reducing tracking error from a reference trajectory. This paper attempts to bridge over the gap between these two approaches. We develop a design theory of trailer systems with passive steering. The designed systems show a good performance in practical path following, and accept the chained form transformation and nonlinear control strategies for nonholonomic systems.