Application of BWS injection type servo driver in injection molding machine

1. The solution of BWS injection type servo driver on the Injection Molding machine

The injection molding machine with hydraulic system is divided into vertical and horizontal.

1.1 Solutions for vertical injection molding machines

In the vertical injection molding machine with dozens of grams, the oil pump uses a gear pump, the capacity of the motor is also small, and the electrical control circuit is relatively simple. During installation, connect the dedicated servo driver of the injection molding machine directly to the power supply circuit of the motor, and then send the signal of the flow proportional valve (0 ~ 1A) to the corresponding port of the inverter after being converted into a 4 ~ 20mA signal. With changes in the processing process, the flow of hydraulic oil is also changing. Generally speaking, it is better to use a flow signal with a relatively larger change in relative value as the control signal. The change in the control signal has a larger range of frequency adjustment for the servo drive; while the change in the relative value of the pressure signal is less, the range for the frequency adjustment of the servo drive is smaller. . If the range of servo drive frequency adjustment can not meet the technological requirements, you can use the servo drive function "frequency gain" to adjust. The special servo driver for injection molding machine adds 0 ~ 1A signal conversion link on the basis of the servo driver, which is more convenient to use.

1.2 Solutions for horizontal injection molding machines

Above 60 grams are all horizontal injection molding machines, 60 to 500 grams injection molding machines, some are one oil pump, some are two oil pumps. An oil pump injection molding machine, the process of installing a dedicated servo drive for the injection molding machine is the same as the transformation of the vertical injection molding machine: the signal of 0 to 1A is still taken from the flow proportional valve as the speed adjustment signal of the servo drive, although the speed adjustment signal The hydraulic circuit component feeds back to the servo, but there is no given signal in the control circuit, so the control is still an open loop control mode. Also because of energy saving, there may be more than one oil pump for large and medium-sized injection molding machines, such as Mitsubishi 850-MM, 1300-MM, 1800-MM, 2000-MM injection molding machines have three oil pumps. Corresponding to the injection molding process, in the mold clamping stage, the required system pressure is low. At this time, only the 1 # oil pump works. When the system pressure required in the mold clamping stage is high, the 2 # oil pump is put into work again. The highest pressure is required, three oil pumps are put into operation at the same time, the pressure required for demoulding and mold opening is lower, and then stop the operation of 3 # and 2 # oil pumps. As long as it is turned on, the 1 # oil pump will always run. Using three small oil pumps to work intermittently at different process stages is more energy efficient than using one large pump to keep running.

How to transform an injection molding machine with more than two oil pumps? Here, the transformation of the Mitsubishi 1800-MM injection molding machine will be used as an example. The Mitsubishi 1800-MM injection molding machine has three 45KW oil pump motors, and a servo drive is used to drive the 1 # oil pump motor. The adjustment signal of the servo drive is taken from the flow proportional valve of the injection molding machine. The flow rate changes. The other two oil pump motors can be driven by two servo drives. However, these two servo drives do not adjust the speed of the motor, and only perform two-bit control, that is, start and stop. The start and stop signals of the control servo drive are taken from the original start and stop signals of the oil pump motor. The upper limit frequency of the servo drive is set below 50Hz, the specific setting value is related to the size of the workpiece to be processed, the material, the temperature of the barrel and other factors. If the operating frequency of the inverter is lower than 50 Hz, energy can be saved. In fact, there is a margin in the design of the injection molding machine, and the oil pressure required for the change in the size of the processed workpiece and the material must also change. If the injection pressure is too large and the clamping force is insufficient, the workpiece will appear flash; if the injection force is insufficient, the plastic in the mold cavity will be dissatisfied and the workpiece will be scrapped; when the holding pressure is insufficient, the plastic will shrink in the thicker part of the workpiece .

Second, the precautions for the installation of special servo drives for injection molding machines

2.1 Selection of servo drive of injection molding machine

The load nature of the injection molding machine is constant torque type, the mechanical characteristics are harder, and the dynamic characteristics require higher. The servo driver for injection molding machine adds a 0 ~ 1A signal conversion link on the basis of the general frequency converter to improve the performance.

Considering that the time of each stage of the injection molding process has certain requirements, the acceleration and deceleration time of the servo drive should be short, generally 1 second, and the capacity of the servo drive should be selected according to the actual situation. Therefore, before selecting the capacity of the servo drive, the actual maximum load current of the oil pump motor in the power frequency state of the injection molding machine during each process should be measured as a basis for selecting the capacity of the servo drive. The rated current of the servo drive is preferably 1.1 ~ 1.5 times of the rated current of the control motor. The voltage level should be consistent with that of the control motor. In this way, the servo drive capacity may need to be increased by one-level selection.

2.2 Have a backup system

After the injection molding machine special servo drive is installed, the power frequency starting circuit should be used as a backup, so that once the injection molding machine special servo drive fails, the power frequency can also be used to start the oil pump motor to continue running to reduce the injection molding machine special type. The economic loss caused by the failure of the servo drive.

2.3 Signal extraction points of frequency converters for injection molding machines

Take the flow signal (0 ~ 1A) of the double proportional valve and send it to the corresponding port of the servo driver after being converted into a signal of 4 ~ 20m. The flow signal takes a relatively large value as a control signal to expand the adjustment range. The relative value of the pressure signal changes little, and the adjustment range of the servo drive frequency is a little smaller. If the adjustment range of the servo drive cannot meet the needs of the forming process, it can be adjusted with the "frequency gain" function of the servo drive.

2.4 Precautions before commissioning

It is relatively simple to install the servo drive for the injection molding machine, but you should understand the working conditions of the injection molding machine in detail, familiarize yourself with the injection molding machine process, and pay attention to the following items during commissioning: carefully observe whether the injection molding machine is running normally and whether the oil pump motor is often Overload state; observe the potential of power saving transformation of injection molding machine according to the mold and injection process of injection molding machine; pay attention to the positive and negative polarities of control signal lines and do not connect them reversely; signal lines and main circuit lines should be separated and wired.

2.5 Interference of the frequency converter for injection molding machine on the digital instrument

Nowadays, servo drives are widely used in injection molding machines. The output current contains harmonic components, which may cause interference to the injection molding machine. The most susceptible is the temperature control instruments. Therefore, anti-interference measures should be taken when installing the servo drive. The frequency converter needs to install input and output reactors or high-frequency magnetic rings, etc .; the control line of the servo drive should be shielded; the chassis must be reliably grounded; do not make the input and output cables of the servo drive parallel to the control signal line of the servo drive Or bundled together; when the servo drive is installed inside the injection molding machine, special attention should be paid to ventilation and heat dissipation.

Three, debugging common problems and processing methods

Due to the particularity of the injection molding machine process, various failures will be encountered during the installation of the dedicated servo drive for the injection molding machine. The following are the problems and solutions that are often encountered during the installation of the injection molding machine servo.

3.1 The frequency of the servo drive for the injection molding machine does not change

Because the servo drive uses the injection molding machine valve-controlled current signal for speed regulation, after the servo drive runs, the frequency shows 0.0 (some servo drives show 0). The main reason is that the signal polarity is reversed; the signal is wrong; the signal wiring The port is not consistent with the parameter setting; the auxiliary power supply of the injection molding machine is faulty. If this kind of fault occurs, it is necessary to find out whether the injection valve control type is current signal, voltage signal or pulse control signal (some models), and the positive and negative polarity of the signal Whether it corresponds to the servo drive control terminal.

3.2 Noisy pump

After the servo drive of the injection molding machine runs, some injection molding machines will make abnormal noises. At this time, it should be judged where the noise source is from the motor or the oil pump. If it is the noise of the oil pump, the possible reasons are: the injection machine has too little hydraulic oil. Air inhalation; oil filter or oil path of the injection molding machine is blocked; the oil pump blade of the injection molding machine is worn more seriously; the oil pump of the injection molding machine should be checked first before encountering the situation, and it can be operated only after the fault is eliminated. There is an abnormal situation of the oil pump noise, at this time, the speed signal is appropriately increased.

Fourth, the technical advantages of BWS injection-type servo drives in the injection molding machine industry

4.1 BWS injection type servo drive adopts current vector control mode, the starting torque is large, 0.5 Hz can reach 150% of the rated torque; the dynamic response is fast, the step torque response time is "200 ms; the speed stability accuracy is 0.5%. The dynamic response is fast, which effectively solves the chronic diseases that have troubled the post-processing cycle of the servo drive used in the injection molding industry.

4.2 The unique torque control performance of the BWS injection-molded servo drive can effectively control the overcurrent without affecting the instantaneous torque. .

4.3 The corresponding relationship between the analog input and frequency of the Z series servo drive can be set as a broken line type, and two inflection points can be set, which is convenient to meet the strong pressure required for mold clamping. At the same time, the control characteristics of the servo drive enable the load current to be effectively controlled.

4.4 Through the peripheral connection terminal, it can directly receive the current signal of 0 ~ 1A, and the speed control signal can be directly obtained from the proportional flow valve.

4.5 It can accept the signal of 0 ~ 1A current and the voltage signal of 0 ~ 10V to compensate the collected signals of some process sections of the injection molding machine to achieve the perfect control effect.