Jian Ruan

Electrohydraulic Synchronizing Servo Control of a Robotic Arm

The large robotic arm is usually driven by the electrodraulic synchronizing control system. The electrodraulic synchronizing system is designed with the digital valve to eliminate the effect of the nonlinearities, such as hysteresis, saturation, definite resolution. The working principle of the electrodraulic synchronizing control system is introduced and the mathematical model is established through construction of flow rate equation, continuity equation, force equilibrium equation, etc. To obtain the high accuracy, the PID control is introduced in the system. Simulation analysis shows that the dynamic performance of the synchronizing system is good, and its steady state error is very small. To validate the results, the experimental set-up of the synchronizing system is built. The experiment makes it clear that the control system has high accuracy. The synchronizing system can be applied widely in practice.

Actuation and Control of a Micro Electrohydraulic Digital Servo Valve

Structure of the micro digital servo valve is given. A micro stepper motor is used as electrical-to-mechanical interface of the valve. A special mechanical device is designed to convert the rotation of the stepper motor into the linear motion of the spool. This moving conversion device functions through an eccentric ball head rigidly connected to the axis of the stepper motor and plugged into a slot at the central spool land. While the stepper motor rotates, the eccentric ball head will actuate the spool to make a linear motion. Unlike conventional servo or proportional valves, in which the spool is forced to central position by a spring force, when the current supply is switched off, the digital valve has a program to control the spool to its central position each time the electrical power supply is switched on or off. The two end screws are used to adjust the position of the sleeve to sustain a mechanical central position coincided with electrical central position given by the stepper motor after initialization. The adjustment has to be carried once before the first time the servo valve is put into service. This paper presents theoretical analysis and experimental study of dynamic characteristics of the proposed micro digital servo valve. Experimental results demonstrated that the valve takes the advantage of high accuracy and fast response.

Dynamic Characteristics and Stability Analysis of Two-Dimensional (2D) Electro-Hydraulic Proportional Directional Valve

A 2D electrohydraulic proportional directional valve is proposed, which integrates both direct and pilot operation of the valve. In this valve, the output magnetic force of the proportional solenoid is converted to rotate the spool through a thrust-torsion coupling and thus the pressure in the valve sensitive chamber is varied. The varied pressure exerted on the areas of the spool end produces a hydrostatic force to move the spool linearly, which will rotate the spool reversely. Theoretical analysis is carried to the proposed valve and the effects of the key geometric parameters on the dynamic characteristics of the 2D valve and stability are investigated. Experiments are also designed to access to the characteristics of the valve working under direct and pilot operation. The 2D electrohydraulic valve can work properly for both direct operation and pilot operation. The hysteresis and frequency response are measured and the results are within the acceptable range in practical engineering application required of the directional proportional valve.Copyright

Parametric Simulation on Torque-Angle Characteristic of Rotary Electromagnet with Low Inertia

Since conventional electro-mechanical converter of 2D digital valve had limitations of large inertia and low dynamic response, a novel low inertia rotary electromagnet with coreless rotor structure was proposed. The axial magnetic flux generated by permanent magnet and the radial magnetic flux generated by excitation coils were superimposed and then electromagnetic torque was produced to drive rotor to track the input signal simultaneously. Based on the approach of 3D finite element electromagnetic field simulation, the influence of key structure and operating parameters such as excitation ampere turns, working air gap, tooth height, tooth width and wall thickness of coreless rotor on torque-angle characteristic was discussed. The result obtained provides a certain reference value on the structural optimization of electro-mechanical converter of 2D digital valve.

Drive Control of Dithering Table for Grinding

In grinding viscous materials, such as stainless steel, aluminum and many polymeric materials, the application of a dither on the workpieces proves to be an effective way to enhance the quality of surface finish. A linear stepper motor is utilized for this purpose. By means of the PWM control to the adjacent phase coils, the linear stepper can drive the sliding table to make reciprocating motion and also to produce a desired dither signal, while the grinding is undertaken to the attached workpiece. In this paper, a linear stepper motor is introduced to drive the sliding table and a modulated control strategy is used to control the linear stepper continuously, which also generates an additional dither on the sliding table and the attached workpiece. The dither amplitude can be adjusted by means of the modulated frequency. Experiments are designed to measure the practical dither signals and to verify the effectiveness of improving surface finish quality using a dither. It is demonstrated by both theoretical and experimental results that by means of proposed table drive, a rather wide band of dither signal can be acquired and can meet the most demand of viscous material grinding.

The Image Texture Analysis of the Turning Workpieces Based on FBM Model for TCM

The method of tool condition monitoring based on the theory of Fractional Brownian Motions (FBM) is introduced in this paper. The fractional Brownian surface and the FBM model of image gray-level field are discussed. The image texture of turning workpieces is analyzed using FBM model. The texture characteristic of turning workpiece surface can be expressed by the power spectrum of FBM of the workpiece surface image. The experiment results indicate that the power spectrum of the gray function of the workpiece image line is correlative with the condition of the used tool. The fractal dimension D and the fractal parameter H can be used to recognize the condition of the tool. Introduction In recent years, a lot of researches are done on the auto-monitoring of tool condition, because cutting tool state is a significant factor, which affects the manufacture cost and workpiece quality [1,2]. Among all tool condition monitoring methods, the methods based on image analysis have many advantages. They may get the precious value of the wearing, be convenient for use in industry and work rapidly. The tool condition can be monitored by analyzing the surface state of workpiece. If the cutting tool is in good condition, there should be regular cutting track on the surface of workpiece. While if the tool is wear or breakage, or has accumulated scraps, the track on the surface of workpiece should be disconnected, blurry and abnormal. The texture of the image of workpiece can be analyzed and the corresponding features can be extracted for diagnosing the state of cutting tool. Fractional Brownian motions (FBM) is extended from Brownian motions. It has characters such as zero average value and infinite long relativity. In this paper, the method based on the FBM model for describing the texture features of workpiece surface image will be presented and its application in tool condition monitoring will discussed. The Basic Theory of Fractional Brownian Motions The fractional Brownian motion (FBM) was proposed by Mandelbrot and Ness in 1968[3]. Because of its mathematical simplicity, FBM has become a typical model of calculating the auto correlation signals. Many other stochastic processes including fractal signal model, such as 1/f noise, commonly include FBM model. Suppose that H (0,1), and b0 is a random real number. If random function meets:

A Hydraulic Elastic Feed Drive for Fine Grinding of Non-Circular Element

The hydraulic elastic feed drive utilizes a hydraulic bellows tube as the actuator. While pressure oil is etin, the bellows tube will axially expand and exert a pushing force on the vertical arm of the grinding frame. This pushing force will cause the deformation of the elastic arm and thus the displacement of the grinding head. Within the extent of elasticity, the displacement of the deformation is linearly proportional to the value of pressure. Thus, by controlling the pressure wave form, the desired trajectory of the grinding head can be obtained. A pressure valve is used to create the pressure waves. In this paper, the dynamic characteristics which significantly affect the position accuracy of the grinding head and thus the surface finish quality of the non-circular element are theoretically analyzed. A special experiment has been designed to test the performance of the hydraulic elastic feed drive, in which a constant force is applied to simulate the grinding force while the grinding head is keeping track of the contour of non-circular element. The experimental results demonstrate that the stiffness of the feed drive is large enough to maintain the position accuracy.