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

**Abstract** This paper discusses the hydraulic parameters associated with the test methods of computer technology in throttle speed control circuits, and analyzes the test results. **Keywords**: Control Circuits, Parametric Test Systems **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 motion transmission, wide speed range, high torque capacity, and ease of automation. Both the main movement and feed movement of machine tools require precise speed control. In the hydraulic system of a machine tool, the speed control loop plays a crucial role, significantly affecting the overall performance of the system. Currently, there are three main types of speed control loops in machine tool hydraulic systems: (1) throttle speed control loop; (2) volumetric speed control loop; (3) combined volumetric-throttle speed control loop. This paper introduces the application of computer testing technology in analyzing the speed-load and power characteristics of throttle speed control loops, compares actual test curves with theoretical ones, and evaluates 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 various speeds of the actuators are determined by the flow rate Q1 through the throttle valve entering the actuator and the effective working area A1 of the working chamber, as given by: $$ v = \frac{Q_1}{A_1} $$ Where: - $ v $: actuator speed, m/s - $ Q_1 $: actuator flow, 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 movement speed. The excess oil $ \Delta Q $ flows back 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 rate returning to the tank, m³/s The force balance equation for the piston is: $$ p_1 A_1 = F + p_2 A_2 $$ Where: - $ p_1 $: operating pressure of the actuator, Pa - $ F $: load, N - $ p_2 $: return chamber pressure (back pressure), Pa Neglecting pipe pressure loss, $ p_2 \approx 0 $, so: $$ p_1 = \frac{F}{A_1} $$ Equation (4) 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 into the actuator, $ 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 If pipeline pressure loss is neglected, the relief valve adjustment pressure $ p_p $ should be set according to the maximum pressure required under the maximum load plus the throttle valve pressure difference. During work feed, some oil always flows back to the tank through the overflow valve, keeping it in an open state. The inlet pressure of the throttle valve is maintained at a constant level after being set by the overflow valve. The flow entering the actuator is calculated using: $$ Q_1 = C A_j (\Delta p)^{\phi} = C A_j (p_p - \frac{F}{A_1})^{\phi} $$ Where: - $ C $: coefficient - $ \phi $: throttle index depending on orifice shape, fluid state, and oil properties - $ A_j $: orifice flow area, m² For elongated orifices, $ \phi = 1 $; for thin plate orifices, $ \phi = 0.5 $; values between 0.5 and 1 are common. From Equation (8), it is clear that when the throttle valve opening is fixed, the actuator speed changes with the load. For accurate measurement, the load is provided by an electro-hydraulic proportional relief valve. The fuel tank outlet is connected to the inlet of the proportional relief valve, and the load $ F $ is replaced by the inlet chamber working pressure $ p_1 $ during testing. **1.2 Relationship Between Speed and Load – Speed-Load Characteristics** The speed-load characteristic curve is evaluated using the speed rigidity index, which reflects how the speed regulation loop responds to load changes and its stability at that point. **1.3 Power Characteristics of the Hydraulic Pump Output Power** The output power of the hydraulic pump is given by: $$ N_p = p_p Q_p $$ Where: - $ N_p $: output power of the hydraulic pump, W When 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. Computer Test System Software and Hardware Design** **2.1 Hardware Design** The test system consists of an upper and lower computer. The upper computer includes a 586 microcomputer and a printer. The lower unit comprises an 80C196KB single-chip minimum measurement and control system, pressure sensor, proximity switch, and relay. The hardware configuration is shown in Figure 2. **2.2 Software Design** Software is a powerful tool for computer monitoring, offering great flexibility in module design, human-computer interaction interfaces, and module configuration. This system software includes both upper and lower computer software. The upper computer software handles command transmission, load pressure value delivery, parameter echoing, data processing, display, and curve printing. It is written in Visual Basic 5.0, providing a user-friendly interface and easy operation. The lower computer is responsible for 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, signal amplifier, and filter circuit for A/D conversion. The working pressure $ p_1 $ reflects the load $ F $. (2) **Speed Measurement**: Proximity switches K1 and K2 send signals to the 80C196KB high-speed input channels HSI0 and HSI1. The time difference between the two switches is used to calculate the single-stroke working time of the hydraulic cylinder. The distance between the two switches is measured before testing and stored in the EEPROM. The actuator speed is calculated as: $ v = S / T $. (3) **Throttle Opening**: The throttle valve opening is manually adjusted. (4) **Load Pressure**: The outlet pressure of the load is proportional to the inlet cavity of the relief valve. The load pressure is converted using the AD7520 for D/A conversion, and the electro-hydraulic controller regulates the proportional relief valve to maintain constant pressure. The output pressure of the proportional relief valve has a linear relationship with the input current signal, allowing pressure adjustment by varying the current. This is achieved by sending digital values from the AD7520 to the microcontroller. **3. Analysis of Test Results** In Figures 3 and 4, solid lines represent actual test curves, while dashed lines represent theoretical curves. The test data was fitted using the least squares method. It can be seen from the figure that the actual test curve closely matches the theoretical curve, indicating that the designed system is feasible. The test system can also be adapted for testing other performance aspects of the machine tool's hydraulic drive system.

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