Structural characteristics of the automatic feed c

2022-10-19
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Structural characteristics of the automatic feed control system of the tool holder of the gantry planer

the traditional electrical control system of the gantry planer generally adopts the contactor relay control technology. Due to the use of hard point contact and complex wiring, contact failures often occur in the electrical system, making the door planer of Longhe, a multinational company in the leading position in the utilization field of the composite industry, often in the state of shutdown and maintenance, which can not guarantee normal production. The author has used PLC to transform the electrical control system of several gantry planers, and summarized a set of mature solutions for the control of each moving part of the gantry planer. This paper mainly introduces a kind of automatic tool feeding control system using PLC to control the governor and speed reducer. This scheme replaces the original mechanical feed control mechanism, greatly improves the feed accuracy and operability, and has good portability. It can be widely used in the feed system control of various machine tools

take the electrical control system of BQ 2020 gantry planer as an example, its tool rest feed mechanism is a mechanical feed mode, and its transmission diagram is shown in the following figure. The worm is driven by the motor to drive the worm gear to rotate. When the gear is in the left position, the feed mechanism is in the feed position, the coupling 1 and coupling 2 are combined, and the feed mechanism is in the fast position. When the gear is in the right position, the adapter 3 and adapter 4 are combined, and the overrunning clutch drives the gear to rotate. By changing the rotation angle of the overrunning clutch, the gear rotates at different angles, so as to obtain different feed rates of the tool holder. The traditional gantry planer mostly adopts this type of tool rest feed mechanism, which is a typical intermittent feed movement. In the actual use process, the feed motor has frequent positive and negative rotation, large mechanical impact, many electrical faults, the overrunning clutch is easy to wear, and the phenomenon of uneven or weak feed often occurs. This kind of mechanism has many faults, and the overall improvement of the industrial ecological chain is obvious and the amount of maintenance is large. The automatic feed control scheme proposed in this paper can effectively solve these problems

transmission diagram of the feed mechanism

1 overall transformation scheme

the main control system of the transformed gantry planer adopts PLC to realize the automatic control of all its working processes, including the up and down of the beam, the movement of the tool rest, the lifting and falling of the tool, the automatic reciprocating movement of the workbench, interlock protection, alarm, etc. The hardware design of PLC is basically carried out according to the routine. In this design, instead of directly using the output relay of PLC to drive the AC contactor, a 24 V DC relay is added behind each output contact. Using the contact of this relay to drive the load can not only expand the output points, improve versatility, but also protect the output relay of PLC. Among them, the start, stop, forward and reverse rotation and speed regulation of the workbench drive motor are completed by the PLC control speed regulation device, replacing the original relay contactor control system and the AC and DC generator set drive device. The original motor is still used to lift the beam, and the original electromagnet is still used to lift the knife, but they are all controlled by PLC. The overall system control structure of gantry planer

2 tool rest automatic control scheme

2.1 control of tool rest working mode

tool rest working mode proposed in this paper

the tool rest of gantry planer is divided into vertical tool rest, left tool rest and right tool rest. Its action principle is basically the same, but its position is different. Now take the vertical tool rest as an example

the movement of the tool rest is divided into two working modes: manual rapid movement and automatic feeding. The tool rest working mode selection switch on the control cabinet panel sends instructions to PLC for selection. The output frequency of the frequency converter is given by two potentiometers, and wr1 determines the fast-moving speed; WR2 determines the automatic feed speed; The operator shall adjust it at any time as required

when it is necessary to quickly move the tool rest for tool setting, the tool rest working mode selection switch selects the "fast move" mode. The button controls the state of the frequency converter through PLC, and then controls the start and stop of the motor operation. The speed of the motor is given by wr1

when the automatic feed of the tool rest is required, the tool rest working mode selection switch selects the "feed" mode. At this time, the speed of the motor is given by WR2. Every time the workbench changes from forward to backward, PLC turns on the power supply of the tool lifting electromagnet, the planer is lifted, and the tool holder completes the feeding action at the same time. When the workbench changes from backward to forward, the electromagnet coil for lifting the knife is powered off, and the planer spring returns and falls. When the automatic feeding stroke ends, the tool rest hits the travel switch, and the tool rest returns quickly at a fast moving speed. Another travel switch can be set to control the stop of the tool rest, or it can be stopped manually by the operator. In addition, there is a manual tool lifting control switch used when selecting the tool holder

2.2 control of tool feed amount

when the tool is fed, the PLC controls the start and stop of the tool feed motor through the frequency converter speed regulating device, and the tool feed amount is determined by the time △ t of each motor operation and the speed of the motor

if the rotation speed of the motor is n rpm, the rotation time of each feed is △ T seconds, and the pitch of the transmission lead screw is l mm, then the feed equivalent is:

2016

δ= △t × n × In l/60 (mm) (1)

(1), the pitch l of the transmission lead screw is fixed, △ t is set by professionals in PLC through modifying program parameters, and generally does not need to be changed. Under the condition that △ T and l remain unchanged, the automatic feed can be adjusted by adjusting the speed of the motor through the speed adjustment potentiometer WR2 on the control cabinet, which is convenient for workers' on-site operation

2.3 accuracy control of tool feed amount

generally speaking, PLC can well guarantee the accuracy of △ T, and the accuracy of the pitch l of the transmission lead screw can also be guaranteed, so the stability of the motor speed is the key to ensure the accuracy of tool feed amount

the feed amount of the tool holder of the gantry planer during automatic feed is usually a few millimeters. If the lead screw is directly driven by the motor, the motor speed should be adjusted very low accordingly, and the change rate of the motor speed is high under the low-speed state. At the same time, it is difficult to accurately control the starting time of the AC asynchronous motor, which will cause large errors. In order to reduce the error, we install a digital tube between the motor and the tool holder transmission screw to check whether the voltage of the digital tube is normal? For the maintenance method, refer to Section 1 of nixie tube maintenance in Chapter 1. In this way, the motor can work at a higher speed and the time can be extended. The error caused by unstable speed and uncertain starting time can be greatly reduced

for example, if the feed rate is 2 mm and the pitch l of the transmission lead screw is 2 mm, the lead screw is directly driven by the motor, and the motor speed is adjusted to 20 r/min, according to the ideal situation, the motor does not need the starting time, and the motor running time needs 3 s can be calculated from formula (1). However, if the starting time of the motor changes from ± 0.6 s, it may cause an error of about 20%. If we add a 30 ∶ 1 accelerator, the error can be controlled within 1%, which can meet the processing requirements. In the actual design, because the rotation time setting and speed adjustment of the motor have good degrees of freedom, the setting of the reduction ratio of the reduction gearbox mainly considers the requirements of the rated speed and feed speed of the motor, so that the motor can have high work efficiency and stability

3 design of the driving power supply of the feed mechanism

the gantry planer workbench has two driving schemes of DC and AC, and the driving scheme of the feed mechanism also has two kinds of AC and DC. If DC motor is selected, DC digital speed regulation devices of various brands can be used for control. If AC motor is selected, frequency converters of various brands can be used to regulate the speed of various AC motors

3.1 DC drive mode

taking SSD 950+ as an example, it is a full digital DC speed regulating device, which uses an internal current loop and an external speed loop to control the DC motor. Armature voltage feedback can be used, with IR compensation, coding feedback or analog speed measuring motor feedback; Considering the working environment and cost performance, the speed measuring motor feedback is selected in this scheme, and the speed range is 100:1. Its working principle is

mb is a DC motor, BR is a DC speed measuring motor, the tool rest moves quickly when the relay contact ka16 controlled by PLC is closed, the tool rest feeds when ka17 is closed, and wr1 and WR2 are speed regulating potentiometers. The motor rotates forward when ka20 and ka28 are closed, and reverses when ka21 and ka28 are closed. Ka28 is a normally open contact for emergency shutdown in case of failure. It is in closed state when powered on during normal operation. When used in the feed mechanism, it is required to set the tool accurately, with high machining accuracy, and the shutdown time is set to the lower limit of the standard mode of 0.1 s

3.2 AC drive mode

the atv31 series frequency converter of Schneider company of France is used as the speed controller of the feed motor, which provides rich software functions, simple operation, small size, space saving, and programmable logic input. Taking the atv31hu40n4 frequency converter used in this paper as an example, its applicable motor is a 4 kW three-phase AC motor. How to use it

m refers to the feed motor, RZ refers to the motor braking resistance, Po refers to the positive polarity of the DC bus, and there must be a common connection between it and pa+. Ka16 and ka17 are relay contacts controlled by PLC, which respectively control the rapid movement of the feed motor and the feed of the tool holder. The speed of the motor is adjusted by potentiometers WR3 and wr4 installed on the control cabinet respectively. Ka20 and ka21 control the forward and reverse rotation of the motor respectively, so as to determine the direction of rapid movement and feed, Ka29 is a normally open contact for emergency shutdown, which is closed during normal operation. The working state of the system is monitored by PLC, and the power supply of the motor is disconnected in case of fault

4 conclusion

in the process of reforming the electrical control system of multiple gantry planers, the author developed a general automatic feed control system for the tool holder of gantry planers on the basis of studying the structural and performance characteristics of various feed mechanisms. The system adopts PLC and speed regulating device, which greatly simplifies the electromechanical control structure. By adding a reducer between the drive of the tool feed screw and the motor, the error caused by the speed stability and the uncertainty of the starting time is reduced, and the accuracy of the tool feed is guaranteed. Practice has proved that the system has advanced design, high cost performance, large speed regulation range, simple structure, reliable operation and strong portability. It can be widely used in the electrical control system transformation of various types of gantry planers, and also has a good reference value for the speed regulation control of other AC and DC motors

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