Abstract hydraulic parameters associated with the test amount of computer technology testing methods throttle speed circuit, and the test results were analyzed.
Keywords control Circuits Parametric Test Systems
Research on testing system for hydraulic throttle and speed regulating performace of machine tool
Xu Chuangwen, et al
Hydraulic transmission is more and more widely used in the speed control system of the machine tool because the transmission of the movement is smooth and uniform, the speed range is wide, the transmission torque is large, and the automation is easy. The main movement and feed movement of the machine tool have high requirements on the speed. In the hydraulic system of the machine tool, the speed control loop occupies a very important position. The performance of the machine has a decisive influence on the system. At present, there are mainly three types of speed control loops in the hydraulic system of machine tools: (1) throttle speed control loop; (2) volume speed control loop; (3) volume throttle speed control loop. This article mainly introduces the application of computer testing technology in speed-load characteristics and power characteristics of throttle speed control loops, testing related parameter points, and comparing actual test curves with theoretical ones to test and evaluate the performance of the designed debugging loop. Good or bad.
1 throttling speed control circuit characteristics analysis
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 into the actuator and the effective working area A1 of the working chamber, ie
v=Q1/A1(1)
Where v - actuator speed, m/s
Q1 - actuator flow, m3/s
A1——working area effective area, m2
By adjusting the opening of the throttle valve, Q1 can be adjusted to adjust the movement speed of the actuator. The excess oil ΔQ flows back to the tank via the relief valve. When the leakage is not considered, the continuity equation is available
Qp=Q1+ΔQ
Where Qp - pump outlet flow, m3 / s
ΔQ - Flow rate of the relief valve back to the tank, m3/s
The force balance equation of the piston is
p1A1=F+p2A2(3)
Where p1 - actuator operating pressure, Pa
F - Load, N
P2——pressure of oil return chamber (usually called back pressure),Pa
Excluding pipe pressure loss, p2≈0, then
P1=F/A1(4)
Equation (4) shows that the working pressure p1 varies with the load F. The hydraulic pump outlet pressure pp is set by the relief valve. In order to ensure the flow of oil through the throttle valve into the actuator, pp must be greater than p1, ie there should be a pressure difference on the throttle
Δpj=pp-p1=pp-F/A1(5)
Or pp=p1+Δpj=F/A1+Δpj
Where Δpj - pressure difference between throttle valve, Pa
Pp - pump outlet pressure, Pa
If the pressure loss of the pipeline is neglected, the adjustment pressure pp of the relief valve should be set according to the maximum pressure required under the maximum load plus the pressure difference of the throttle valve. When working feed, in order to achieve speed regulation, there is always a part of the excess oil flowing back to the tank through the overflow valve, so the overflow valve is in the normally open state, and the inlet pressure of the throttle valve is basically maintained after the pressure is set by the overflow valve. change. The flow calculation formula for entering the actuator is
Q1=CAjΔpφj=CAj(pp-F/A1)φ(7)
In the formula C—the coefficient φ—throttle index determined by the orifice form, liquid state, and oil properties. For the elongate hole φ=1, for the thin plate hole φ=0.5, the value between the two is φ=0.5 to 1
Aj - orifice flow area, m2
From equation (8), it can be seen that when the opening degree of the throttle valve is fixed, the speed of the actuator changes with the load. For accurate measurement, the load is provided by an electro-hydraulic proportional relief valve. The outlet of the fuel tank is connected to the inlet of the electro-hydraulic proportional relief valve. The load F is replaced by the working pressure p1 of the inlet chamber for testing.
1.2 Speed - the relationship between the load element and load characteristics <br> speed governor loop execution, referred to the speed - load characteristic. The speed-load characteristic curve is further evaluated by the speed rigidity index, which can reflect the speed of the speed regulation loop at the point affected by the load and the speed stability at this point.
1.3 <br> power characteristics of the hydraulic pump output power
Np=ppQp(9)
Where Np - the output power of the hydraulic pump, W
When neglecting leakage and friction loss, the active power output by the hydraulic cylinder is
N1=p1Q1=p1A1v=Fv(10)
The power loss of the loop is
ΔÎ=Np-N1=ppQp-p1Q1
=pp(Q1+ΔQ)-(pp-Δpj)Q1
=ppΔQ+ΔpjQ1=ΔN1+ΔN2
Where ΔN1=ppΔQ overflow loss, W
ΔN2=ΔpjQ1 throttling loss, W
2 Computer Test System Software and Hardware Design
2.1 Hardware Design <br> test system consists of upper and lower bit machine. The upper computer consists of 586 microcomputers and printers. The lower unit is composed of the 80C196KB single-chip minimum measurement and control system, pressure sensor, proximity switch and relay. Its hardware composition principle is shown as in Fig. 2.
<br> 2.2 software design software is a powerful tool for computer monitoring huge advantage reflected. The design of each functional module, the interface of the human-computer interaction interface, and the configuration between modules are quite flexible. This system software is composed of upper computer software and lower computer software. The host computer software completes command transmission, conveying load pressure values, echoing parameters, data processing, display, and printing curves. The software design is all compiled with Visual Basic 5.0. It has a good man-machine interface environment and menu prompts. It is easy to operate.
The lower computer mainly completes the real-time data acquisition of the analog pressure, the detection of the switch signal, and sends the collected data to the upper computer regularly. The software is compiled in assembly language. The detection methods of the parameters are as follows:
(1) Pressure measurement The working pressure p1 and the pump outlet pressure pp are sent to the ACH4 and ACH5 tens A/D analog conversion channels of the single-chip microcomputer through a pressure sensor, a signal amplifying circuit, and a filter circuit to complete the analog-to-digital conversion. The working pressure p1 in the test reflects F.
(2) The speed measurement close to the switch signal K1, K2 send 80C196KB high-speed input channel HSI0, HSI1, trigger jump time difference for the hydraulic cylinder a single-stroke working time, the two proximity switch distance is S (adjust the distance between the two switches before testing, After adjusting, measure the size of S, and send the S value back to the EEPROM of the measurement and control system by the setting parameter.) The actuator (hydraulic cylinder) speed is calculated as: v = (S)/(T).
(3) Throttle opening The opening of the throttle valve is manually adjusted.
(4) The pressure of the hydraulic cylinder at the outlet of the load pressure is proportional to the relief valve inlet cavity. The load pressure is converted by the AD7520 to complete the D/A conversion and the electro-hydraulic controller controls the proportional relief valve to provide constant pressure. The hydraulic pressure output by the proportional relief valve has a linear relationship with the magnitude of the input current signal, and the output pressure of the proportional relief valve can be changed by changing the magnitude of the current. The current signal size change is achieved by sending the AD7520 digital quantity to the microcontroller.
3 Analysis of test results
The solid lines in FIGS. 3 and 4 indicate actual test curves, and the dashed lines indicate theoretical curves. The test data was fitted with data processing using least squares.
It can be seen from the figure that the actual test curve is basically consistent with the theoretical curve, which shows that the designed system is feasible, the test system is slightly changed, and can also be used as a test for other performances in the hydraulic drive system of the machine tool.