Parallel robotic automated docking method for realizing space segment assembly

PurposeHydrostatic thrust bearing is a key component of the vertical CNC machining equipment, and often results in friction failure under the working condition of high speed and heavy load. The lubricating oil film becomes thin or breaks because of high speed and heavy load and it affects the high precision and stable operation of the vertical CNC machining equipment; hence, it is an effective way of avoiding friction failure for achieving the oil film shape predictionDesign/methodology/approachFor the hydrostatic thrust bearing with double rectangular cavities, researchers solve the deformation of the friction pairs in hydrostatic bearing by using the computation of hydrodynamics, elasticity theory, finite element method and fluid-thermal-mechanical coupled method. The deformation includes heat deformation and elasticity deformation, the shape of gap oil film is got according to the deformation of the friction pairs in hydrostatic bearing, and gets the shape of gap oil film, and determines the influencing factors and laws of the oil film shape, and achieves the prediction of oil film shape, and ascertains the mechanism of friction failure. An experimental verification is carried out.FindingsResults show that the deformation of the rotational workbench is upturned along its radial direction under the working condition of high speed and heavy load. However, the deformation of the base is downturned along its radial direction and the deformation law of the gap oil film along the radius direction is estimated; the outer diameter is close but the inner diameter is divergent wedge.Originality/valueThe conclusion can provide a theoretical basis for the oil film control of hydrostatic thrust bearing and improve the stability of vertical CNC machining equipment.

The operating environment underground in coal mines is harsh. During long-term operations, the driving wheel is subjected to heavy load and high wear rate, increasing the demands on the driving performance of the monorail crane, especially when operating on steep slopes. In this work, the dynamic characteristics of the monorail crane drive system are analyzed and the appropriate starting acceleration for heavy load and steep slope conditions is determined. Using the control variable method, the influence of factors such as load, slope, oil property, and wear degree on the load torque during startup process is investigated and the effects of clamping cylinder oil pressure, load torque, and wear degree on the shear stress in the driving wheel adhesive layer are analyzed. Innovatively, the hydraulic circuit is improved, and a clamping circuit capable of outputting two levels of clamping force is designed. In addition, a double-layer nested stochastic response model for the shear stress in the driving wheel adhesive layer is developed and the reliability of the monorail crane drive system under heavy load and steep slope conditions is then assessed. The research indicates that the driving wheel wear degree is the most significant random variable affecting the reliability of the drive system. Results can serve as a reference for the selection of key parameters and safety assessments of the drive system of the mining monorail crane under heavy load and steep slope conditions.

Identification of failure modes of a PEEK-steel gear pair under lubrication

A novel model-based controller for six degree of freedom (dof) parallel manipulator-PID controller with gravity compensation is developed, in order to improve the control precision of six-dof hydraulic driven parallel manipulator with long stroke hydraulic actuator and heavy load. In this paper, six-dof parallel manipulator is described as a thirteen rigid-body systems. The mathematical model of gravity item including upper platform and hydraulic cylinders is built using Kane method in six dimensions generalized coordinates system, based on close-form solutions and Newton-Raphson method, forward kinematics and inverse kinematics of the six-dof parallel manipulator are established. The PID controller with gravity compensation is presented with the feedback of cylinder length of platform, desired trajectories and dynamics gravity as the input. The physical systems of 6dof parallel manipulator are modeled by ADAMS, and the PID controller with gravity compensation is built with Simulink. The whole control system of 6-dof parallel manipulator is obtained by connecting ADAMS plant with PID control system with gravity compensation in Simulink. The simulation of the whole systems is executed in Simulink, the simulation results indicate the PID controller with gravity compensation can eliminate steady state error of 6-dof hydraulic driven parallel manipulator and improve the control precision.

Parallel structures have remarkable characteristics such as high precision, high load capacity, high rigidity and high speed. Therefore, they have received a lot of attention as alternative structures for robot manipulators. This paper reviews the recent results on properties of the parallel manipulator. First, the basics of the link mechanism, which is necessary to understand the structure of the parallel manipulator, is summarized before the structure of the parallel manipulator is defined. Then, the parallel manipulator is compared with the serial manipulator. The singular point of the parallel manipulator and the optimum design of the structure of the parallel manipulator are also discussed.

Tribological behavior of plasma-sprayed metal based solid self-lubricating coatings under heavy load

In order for decreasing the weight of industrial robot manipulator with high stiffness, the sandwich panel structure is adopted for the parallel laser welding robot manipulators. So, about 37% of the weights of robot manipulators is reduced in our research. The straight line and circle welding joint experiments are made by the parallel laser welding robot with three branches. The end precision of the robot is surveyed online by the CMM (Cordinate Measuring Machine). The measurement data indicate that the end position precision of parallel robots is about 0.2mm. The end posture precision is about 0.05 degrees. Laser welding seams are of good qualities. Experimental results verify that the end accuracy of the robot can meet the requirement of laser welding with high precisions and high stiffness. It is feasible that robot manipulators adopt the sandwich plate structure for the accurate operations.

Design and testing of a high precision parallel manipulator with hyperbolic–elliptic flexure hinges

Adaptive robust control of fully-constrained cable driven parallel robots

Double-cylinder parallel manipulators are closed-loop two-degree-of-freedom linkages. They are preferred to use because of their simplicity plus the common advantages of parallel manipulators such as high stiffness, load-bearing, operation speed and precision positioning. Like other parallel manipulators, the output motion of double-cylinder parallel manipulators is not as flexible as two-degree-of-freedom serial manipulators. The motion performance analysis plays a critical role for this type of parallel manipulator to be applied successfully. In this paper, the linkage feasibility conditions are established based on the transmission angle. When feasibility conditions are satisfied, there is no dead position during operation. The workspace is generated by using curve-enveloping theory. The singularity characteristics are analyzed within the workspace. The motion performance index contours within the workspace are produced using the condition number of the manipulator Jacobian matrix. The results of this paper provide guidelines to apply this type of parallel manipulator.

Heavy loads are known to be among the most critical operational factors affecting the behavior of the lubricating oil film within journal bearing related to marine slow speed diesel engines. In light of the fact, a comprehensive investigation was carried out to examine the performance of journal bearing under heavy loads resulting from increased maximum pressure within the combustion chamber. Further, the research test trial procedures have been extended to cover the different speed ranges of 40 rpm, 85 rpm and 105 rpm, as corresponding to the engine loads (40 %, 85% and 100 % respectively), together with the different oil grades of 20W50, 5W40 and 0W30. Universal Journal Bearing Test Rig (UJBTR) was utilized for conducting the experimental test trials due to its capability to contain versatile variations regarding the key operational factors. Experimental test trials basically based on tracing the changes in the oil film pressure distribution and the maximum oil film pressure values, have given insight into the behavior of heavy-loaded journal bearing of diesel engine related to ships. Based all the experimental test trials under optimal and heavy load conditions, oil grade 5W40 was concluded to provide the most optimal operating conditions for all tested speed ranges.

This paper proposes a novel planar electromagnetic-actuated positioning stage. The stage is suspended by the monolithic parallel flexure mechanism, which motion comes from the deformation of the flexure. A linear electromagnetic actuator which consists of a near-uniform magnetic field and four coils is designed and implementation to provide the propelling force for 3-DOF motions. In order to suppress the vibration of the flexure suspension mechanism, an eddy current damper is designed and integrated with the electromagnetic actuator. The non-contact damper is more advanced than the contact damper used in our previous researches. The design traveling range is 3mm × 3mm in planar motion. The experimental results show the vibration of the flexure mechanism could be suppressed by the designed eddy current damper. The results also show the regulation and tracking performance by a well-designed robust adaptive sliding mode controller, which can overcome the disturbance and modeling uncertainty and guarantee a satisfactory performance.

Parallel manipulators have the advantage of high speed and high precision in the theory of mechanisms. This has opened up broad possibilities for the use of parallel manipulators in many fields. But in real applications, due to the inevitable manufacturing tolerances and assembling errors, the actual kinematic parameters of parallel manipulators are always unequal to the nominal values and calibration procedures have to be implemented to compensate the kinematic parameter errors between them. According to the metrology devices adopted, calibration methods of parallel manipulators can be classified into two categories, the external calibration methods and the autocalibration methods. External calibration methods rely on the precise external 3D measuring devices, such as laser tracking systems (Koseki et al., 1998; Vincze et al., 1994), mechanical devices (Jeong et al., 1999) and camera systems (Zou & Notash, 2001; Renaud et al., 2006). With these external devices, one can measure the end-effector position of parallel manipulators and calibrate the kinematic parameters by minimizing either the errors between the measured end-effector positions and the estimated end-effector positions (Masory et al., 1993), or the errors between the measured joint positions and the estimated joint positions (Zhuang et al., 1995; Zhuang et al., 1998). The auto-calibration methods rely on the redundant joint sensors of parallel manipulators, which can be achieved by adding extra sensors to the uninstrumented joints (Baron & Angeles, 1998; Zhuang, 1997; Wampler et al., 1995; Patel & Ehmann, 2000), or by constraining the motion of end-effector or some joints (Khalil & Besnard, 1999; Wang & Masory, 1993). With the redundant joint sensors, extra information can be obtained for the sampled configurations without employing any external measuring devices (Hollerbach & Wampler, 1996; Yiu et al., 2003c; Chiu & Perng, 2004), and the auto-calibration procedure is usually implemented by minimizing a function of closed-loop constraint errors. Obviously, it is more convenient to measure the sampled configurations by the redundant joint sensors than the external 3D measuring devices. especially for the parallel manipulator with inherent redundant joint sensors. But it is

The robot arms used in industry are classified as two categories including the serial robot and the parallel robot. Compared with the serial robots, parallel robots have advantages in high precision, high stiffness, high load, high speed and low inertia. This work proposed and implemented a mechanism to perform spherical motion with merely extra modification of a Delta-based machine and the experimental results showed that this design is practical and stable for usage. According to the quantitative evaluation, the errors are within several millimeters.

Kinematic analysis and error modeling of TAU parallel robot