The hydraulic system is operated automatically according to the program. The process requires that each action must start and finish at a predetermined time and place. Manual operation of hydraulic system also has its action order requirements. The normalization of the action order of hydraulic system is the basic condition for the normal operation, but in fact, the hydraulic system is prone to deviate from the normal movement order and even chaotic situation. It can eliminate the disorder of movement order through the following ways.

1. improve the accuracy of the control signal

The start and stop of hydraulic action is controlled by the control signal, which includes manual operation signal, position signal, pressure signal and time signal.

(1) the important way to improve the accuracy of the operation signal and improve the accuracy of the operation signal is to take measures to prevent misoperation.

Taking injection molding machine as an example, in order to prevent the operator from operating the injection machine without the safety door, the locking measures should be set so that the machine can only enter the automatic operation state only after the safety door is concerned. The injection molding machine also has the mold locking measures, when the mold adjustment operation, other operations can not be carried out.

Fig. 2-32 is an example of a hydraulic circuit for preventing misoperation of hydraulic presses. The rise and fall of the punch 4 is controlled by the hydraulic control reversing valve 1, and the valve 1 is controlled by the manual reversing valve 2 and 3. The operator makes the handle of valve 2 and 3 face up (position), then the punch goes up. If the valve 2 and 3 of the handle down, the punch down, only two handles move, only action, which ensures the accuracy of action.

2) to improve the accuracy of position signal and to improve the accuracy of position signal, the position sensor with high accuracy and reliability is the first choice. At the same time, to ensure that the sensor installation is reliable, the collision block and induction parts should be installed according to the requirements, so as to ensure the correct position signal.

In order to prevent the fault, some measures should be taken to prevent the failure of the position sensor. For example, the opening action of the injection molding machine is composed of two stages: quick opening and slow opening. Fast to slow and stop opening, respectively by the two stroke switch control, which is the first travel switch control X1 rapid prototyping to slow opening, second stroke switch control to stop where the slow opening mold (Fig. 2-33). In the controller made up of PLC, fast opening and slow opening are performed by two intermediate relays (assumed to be K1 and K2). When the X1 fails, it can not terminate the K1 and start the K2, so the hydraulic cylinder will be executed by K1 rapid mold opening, go to the place can not stop, because and the role is to terminate the long and can not terminate the K1. Therefore, the rapid mold opening will continue to the end, resulting in strong vibration and impact. To avoid this, an instruction can be added to the PLC program so that both ends can be terminated and K1 can be terminated. Thus, if the X1 fails, the X2 can terminate the K1 and stop the hydraulic cylinder.

The hydraulic cylinder in the forward and backward process may encounter some action has nothing to do with the current trip switch, such as forward when the control switch back speed switch, speed switch control switch in the back or. Therefore, to take measures to stop any travel switch with current action not touched or induced a control signal error. The basic method is to add interlock command in the controller program, that is, when the hydraulic cylinder performs the forward movement, lock the back action; when the backward action is carried out, the forward movement is locked. Taking the injection cylinder of injection molding machine as an example, the reason is further explained. When the hydraulic cylinder carries out the injection, it undergoes three stages such as first level injection, two stage injection and three stage injection. The switching of the three phases is accomplished by three stroke switches, in which X8 controls a primary injection to a two level injection, a melon control two stage injection to a three level injection, and a field control three stage injection stops. When the hydraulic cylinder is back, the plasticizing and suction are carried out. The X10 is used to control the plasticizing and transferring the glue, and the glue stopping is controlled by the X11. The position of each stroke switch is shown in figure 2-34. The problem here is that when you go forward, you have to go through an unrelated stroke switch. X8 and X7 go through two unrelated stroke switches, X8 and X7. Therefore, the interlocking measures should be taken: when the first injection is performed, the locking and injection of glue will not make the X10 work. Three and two injections were locked during plasticization to make X8 and X7 do not work.

(3) to improve the accuracy of pressure signals, in order to improve the accuracy of pressure signals, the pressure sensor with high accuracy and reliability is the first choice. At the same time, it is necessary to prevent the hydraulic impact in the hydraulic system from sending out the wrong control signal, and the damper can be used to attenuate the hydraulic impact before the pressure sensor. Pressure sensor should be installed in the oil tank near the hydraulic cylinder, installed in the reversing valve and pressure reducing valve, so as to correctly reflect the actual pressure.

In the hydraulic system, the pressure sensor will consistently send the pressure signal to the electrical controller, but only in specific circumstances and at a specific time, the controller can pick up the pressure signal as the control signal. Therefore, in the design of electrical control system, attention must be paid to the timing of the pressure signal to the controller, so as to prevent the pressure signal from disrupting the order of the control system. For example, in the injection molding machine automatic program, the end of the lock action and injection action is started by the pressure signal control. When the locking mode pressure reaches the adjustment value, the pressure relay is connected to the controller's input signal circuit, the controller sends out instructions according to the signal, ends the locking mode and starts the injection. In the injection stage, the clamping pressure may decrease to below the setting value, and the pressure relay will cut off the input signal circuit. At this point, if there are no limiting measures, the injection machine may break the injection, restart the mold locking, which will inevitably lead to confusion. The solution to this problem is to set the locking instructions in the injection program so that the pressure change signal does not affect the normal injection.

(4) to improve the accuracy of time signal and improve the accuracy of time signal, the first choice is to choose a timer with high accuracy and reliability. The timer should have digital display so that it can be adjusted and modified. When designing the electrical controller of the hydraulic device, the timing of the timer should be limited to prevent it from sending out the wrong signal to break the automatic program.

2. improve the accuracy of the hydraulic system itself

(1) the accuracy and hydraulic system with high precision and high reliability of the hydraulic control valve hydraulic control valve response sensitivity and actions in order to close the hydraulic system action is accurate and orderly, hydraulic control valve selection must be of high quality, especially to select all kinds of valve and sequence control valve, failure is inevitable the hydraulic system caused by disorder of the valve.

(2) reasonable design of hydraulic circuit of hydraulic system in order to ensure accurate action, should pay attention to in the design of hydraulic circuit: to take effective measures to prevent various types of hydraulic impact and influence of pressure relay and sequence valve; to take effective measures to prevent mutual interference between hydraulic loop; oil pipeline design hydraulic valves, hydraulic oil drain valve open, to ensure the normal functioning of hydraulic valve.

(3) to prevent the hydraulic oil pollution from hydraulic oil pollution caused by hydraulic valve stuck, rust knot and oil blockage, which will inevitably lead to hydraulic system movement order disorder. Therefore, the design of hydraulic system should pay attention to take effective measures to prevent water, dust and debris pollution of hydraulic oil. Equipment operation and maintenance process should also pay attention to prevent oil pollution.