Research on Hydraulic Throttle Velocity Adjusting Performance Test System for Machine Tools

**Abstract** This paper discusses the hydraulic parameters associated with the testing methods of computer technology applied to throttle speed control circuits, and analyzes the test results. The keywords include control circuits, parametric testing systems, and hydraulic performance. **Research on Testing System for Hydraulic Throttle and Speed Regulation Performance of Machine Tools** Xu Chuangwen, et al. Hydraulic transmission is increasingly used in the speed control systems of machine tools due to its smooth and uniform movement transmission, wide speed range, high torque capacity, and ease of automation. Both the main motion and feed motion of machine tools require precise speed control. In the hydraulic system of a machine tool, the speed control loop plays a critical role in determining the overall performance of the system. Currently, there are three main types of speed control loops in hydraulic systems: (1) throttle speed control, (2) volumetric speed control, and (3) combined volumetric-throttle speed control. This paper introduces the application of computer testing technology in analyzing the speed-load and power characteristics of throttle speed control circuits, comparing actual test curves with theoretical ones to evaluate the performance of the designed control loop. **1. Characteristics Analysis of Throttle Speed Control Circuit** **1.1 Working Principles and Circuit Parameters (Figure 1)** The speed of the actuator is determined by the flow rate Q1 through the throttle valve into the actuator and the effective working area A1 of the working chamber, as expressed by: $$ v = \frac{Q_1}{A_1} $$ Where: - $ v $: actuator speed, m/s - $ Q_1 $: flow rate into the actuator, m³/s - $ A_1 $: effective working area, m² By adjusting the opening of the throttle valve, $ Q_1 $ can be controlled to adjust the actuator's speed. Any excess oil $ \Delta Q $ returns to the tank via the relief valve. Assuming no leakage, the continuity equation applies: $$ Q_p = Q_1 + \Delta Q $$ Where: - $ Q_p $: pump outlet flow, m³/s - $ \Delta Q $: flow returning to the tank via the relief valve, m³/s The force balance equation for the piston is: $$ p_1 A_1 = F + p_2 A_2 $$ Where: - $ p_1 $: actuator operating pressure, Pa - $ F $: load, N - $ p_2 $: return chamber pressure (back pressure), Pa Neglecting pipe pressure loss, $ p_2 \approx 0 $, so: $$ p_1 = \frac{F}{A_1} $$ This shows that the working pressure $ p_1 $ varies with the load $ F $. The pump outlet pressure $ p_p $ is set by the relief valve. To ensure oil flows through the throttle valve, $ p_p $ must be greater than $ p_1 $, creating a pressure difference across the throttle valve: $$ \Delta p_j = p_p - p_1 = p_p - \frac{F}{A_1} $$ Or: $$ p_p = \frac{F}{A_1} + \Delta p_j $$ Where: - $ \Delta p_j $: pressure difference across the throttle valve, Pa - $ p_p $: pump outlet pressure, Pa When pipeline pressure loss is neglected, the relief valve’s adjustment pressure $ p_p $ should be set based on the maximum load plus the throttle valve’s pressure difference. During working feed, some oil always flows back through the overflow valve, keeping it in an open state. The inlet pressure of the throttle valve remains stable after being set by the relief valve. The flow entering the actuator is calculated using: $$ Q_1 = C A_j (\Delta p)^{\phi} $$ Where: - $ C $: coefficient - $ \phi $: orifice index (e.g., 1 for elongated holes, 0.5 for thin plate holes) - $ A_j $: orifice flow area, m² For accurate measurement, the load is provided by an electro-hydraulic proportional relief valve. The fuel tank outlet is connected to the relief valve inlet, and the load $ F $ is replaced by the inlet chamber pressure $ p_1 $ during testing. **1.2 Relationship Between Speed and Load – Load Characteristics** The speed-load characteristic curve is evaluated using the speed stiffness index, which reflects how the speed regulation loop responds to load changes and its stability at that point. **1.3 Power Characteristics of Hydraulic Pump Output** The output power of the hydraulic pump is: $$ N_p = p_p Q_p $$ Where: - $ N_p $: pump output power, W Neglecting leakage and friction losses, the active power output by the hydraulic cylinder is: $$ N_1 = p_1 Q_1 = p_1 A_1 v = Fv $$ The power loss in the loop is: $$ \Delta N = N_p - N_1 = p_p Q_p - p_1 Q_1 $$ $$ = p_p (Q_1 + \Delta Q) - (p_p - \Delta p_j) Q_1 $$ $$ = p_p \Delta Q + \Delta p_j Q_1 = \Delta N_1 + \Delta N_2 $$ Where: - $ \Delta N_1 = p_p \Delta Q $: overflow loss, W - $ \Delta N_2 = \Delta p_j Q_1 $: throttling loss, W **2. Hardware and Software Design of the Computer Test System** **2.1 Hardware Design** The test system consists of an upper and lower unit. The upper computer uses a 586 microcomputer and printer. The lower unit includes an 80C196KB single-chip microcontroller, pressure sensors, proximity switches, and relays. Its hardware configuration is shown in Figure 2. **2.2 Software Design** The software is a powerful tool for monitoring and controlling large-scale systems. It offers flexible design for each functional module, human-computer interaction interface, and module configuration. The system software includes upper and lower computer components. The upper computer handles command transmission, load pressure values, parameter echoing, data processing, display, and curve printing. It is developed using Visual Basic 5.0, offering a user-friendly interface and easy operation. The lower computer performs real-time analog pressure data acquisition, switch signal detection, and regular data transmission to the upper computer. It is written in assembly language. The parameter detection methods are as follows: 1. **Pressure Measurement**: The working pressure $ p_1 $ and pump outlet pressure $ p_p $ are sent to the ACH4 and ACH5 channels of the microcontroller via a pressure sensor, amplifier, and filter circuit for A/D conversion. 2. **Speed Measurement**: Proximity switches K1 and K2 send signals to the HSI0 and HSI1 high-speed input channels of the 80C196KB microcontroller. The time difference between the two switches’ triggers is used to calculate the actuator’s speed. 3. **Throttle Opening**: Adjusted manually. 4. **Load Pressure Conversion**: The load pressure is converted using the AD7520 D/A converter, and the proportional relief valve is controlled to provide constant pressure. **3. Analysis of Test Results** In Figures 3 and 4, solid lines represent actual test curves, while dashed lines show theoretical curves. The test data was processed using the least squares method. The actual curves closely match the theoretical ones, confirming the feasibility of the designed system. Minor adjustments can also make the system applicable for testing other performance aspects of the machine tool’s hydraulic drive system.

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