Its multi-speed function of the speed of each section can be adjusted independently, according to the operation needs to set a variety of different speeds for operation.
The smooth starting and braking characteristics of the inverter reduce the mechanical impact and reduce the structural loss; The starting current is small, which reduces the heat loss of the motor during frequent starting and braking, and prolongs the service life of the motor; The frequency converter itself is a universal standard equipment with high reliability, and the failure rate is extremely low. After the frequency converter is introduced, the failure rate of the whole machine is reduced, the maintenance amount is reduced, and the operation efficiency is indirectly improved.
In order to improve the reliability of the operating device, the multi-stage speed has a smooth speed regulation mode.
The frequency conversion speed regulation has obvious power saving effect in the low speed situation and the acceleration and deceleration process.
This system selects the 616G5 series frequency converter of Yaskawa Company of Japan, which can conveniently realize closed-loop vector control and can achieve up to 1:1000 speed ratio, high-precision speed control, zero speed can reach 150% rated torque, widely used in lifting industry. Each motor is originally wound motor rotor series resistance speed regulation, after changing to frequency conversion speed regulation, it is not necessary to replace the motor, only the motor rotor circuit can be short-circuited.
Design and selection of control system
Lifting equipment involves a series of safety issues, floating crane control system must have good reliability and perfect safety measures, even in the case of operational errors will not lead to safety accidents and equipment damage, so this program uses PLC to achieve safety interlock and anti-error function. All operations are performed by PLC program, except for emergency stop operation which is kept in direct wiring mode. This system selects Siemens 6ES7-200 series compact small PLC products as the core control equipment.
Design and selection of linkage operation platform
Linkage console is the operating position and man-machine interface of the floating crane. Besides the handle cam controller as the basic operator, it is also equipped with various fault signals, emergency stop button, function selection switch and operation key switch.
As the main operating equipment of floating crane, linkage manipulator acts frequently, requires reliability and long service life. This system chooses XKB-E series handle type cam controller of French Schneider company, its operation is agile and reliable, feel is good, service life is as high as each direction 100 million times, with rotate and luffing manipulator is exemple, namely allow left turn right turn and luffing to move forward backward each 100 million times, according to floating crane operation frequency estimation, every manipulator can use about 1 year.
When the lifting or grab part fails, it is necessary to lower the grab. For this reason, the mechanical brake release pedal and the key switch allowing this operation are designed.
Environmental adaptability design and type selection of system
The floating crane is located beside the river, and its main task is to load and unload ore. It works in high temperature, high humidity, high dust and vibration environment, so it is necessary to take measures to control the normal operation of the system.
The four motors and all control cabinets in the main winch room of the floating crane are heating bodies, which will produce very high ambient temperature due to difficulty in discharging heat in summer, which is not conducive to the normal operation of the control system. A forced ventilation device is installed in the chamber to improve the heat dissipation condition.
The hoisting and grab motor has high working continuity. When running at low speed for a long time, due to the low working efficiency of the built-in fan, the heat dissipation capacity is poor, so the external forced air cooling is changed.
Imported cabinet body is adopted for each control cabinet. The closed structure can prevent dust and moisture from entering. Forced ventilation fan with filter cover is installed on the cabinet body to discharge heat in the cabinet. Cabinet body equipped with PLC is equipped with cabinet air conditioner. The system can work normally at ambient temperature of-10-65℃.
All major electrical equipment shall be imported equipment with anti-vibration capability. For the high reliability of the whole control system, the circuit breaker, disconnector, contactor, button signal lamp and other low-voltage electrical appliances are uniformly selected from the famous European brand, the products of German Admiralty-Moeller Company.
3 Specific design of control system
3.1 Several problems in the design of electrical main circuit electrical protection
The branch circuit breaker is used for branch short circuit protection and backup overload protection at the inlet of each branch, and the overload protection, overvoltage and undervoltage protection and other protections of the branch are undertaken by the protection function of the frequency converter itself. The isolation transformer provides the control power supply and supplies power to the PLC, so as to minimize the possibility that the PLC and control elements are disturbed by the power supply and cause abnormal operation. A circuit breaker shall be set at the front end of isolation transformer for short circuit protection and line protection.
Inverter outlet isolating switch
After the motor is overhauled or stopped for a long time, insulation test shall be conducted, and the motor can be put into operation only after passing the test. However, the frequency converter is a power electronic equipment, so conventional insulation test cannot be conducted. Therefore, isolating switches are set behind each frequency converter to disconnect the frequency converter from the motor conveniently when necessary.
Brake unit and brake resistor
When the load of hoisting and grab motor drops, the potential energy of the heavy object will be converted into electric energy, and then the additional braking resistance of the frequency converter will convert the electric energy into heat energy for dissipation, so as to achieve the purpose of stable braking. Rotating and luffing motors are also attached with braking resistors as a means of braking during deceleration. The braking resistor is connected to the frequency converter through the braking unit, and the braking unit can automatically input and cut off the braking resistor as required. The braking resistor is installed on a special resistor mounting bracket outside the control cabinet.
mechanical brake control
The mechanical brake of each motor is controlled by a contactor. The luffing brake power supply is from the back end of the branch circuit breaker, so that only when the converter branch has been electrified, the release of the mechanical brake is allowed. And lift head and grab bucket brake because need to allow grab bucket to fall when breakdown, reason design circuit breaker to try to protect alone.
rotary encoder
In order to prevent the heavy object from sliding down suddenly or the luffing mechanism from leaning forward suddenly after the mechanical brake is released during startup, the frequency conversion speed regulation of hoisting, grab bucket and luffing motor adopts closed-loop vector mode to obtain rapid torque response. The rotation speed detection of the closed loop is realized by a rotary encoder installed at the shaft end of the motor. 3.2 Key points in control system design
PLC is the core of the entire floating crane control system, in addition to the emergency stop button, all operating equipment, testing equipment and execution equipment are linked to each other through PLC. In order to reduce the influence of electrical interference, all inputs and outputs of PLC are connected through inlet and outlet relays except for the signals of the nearby linkage console. The emergency stop button is the backhand section for human intervention in case of emergency. It can work normally even if the PLC function has failed. The signal directly acts on each branch circuit breaker to trip it, and forces the whole floating crane to stop working immediately by cutting off the power supply. All other operation instructions on the linkage console are input to PLC in contact mode, and then PLC controls each frequency converter to make each motor rotate forward and backward, accelerate and decelerate and stop running. There is a one-to-one correspondence between the operation instruction and the running direction and speed of the motor, and the interlocking relationship is realized by PLC.
Speed regulation instruction and frequency converter status signal
PLC sends operation, stop, operation direction and speed classification instructions to each frequency converter in contact mode, and collects state signals such as operation and fault of frequency converter.
speed feedback signal
The speed feedback signal is collected by the rotary encoder and sent directly to the frequency converter through the PG card to participate in the closed-loop control.
Contactor control and feedback
All mechanical brakes are required to be released reliably when the frequency converter starts to operate, and to be engaged reliably when the frequency converter stops operating for some reason. Its function is realized by controlling the closing and release of contactor after logical judgment by PLC, and the auxiliary contact signal of contactor is adopted to judge whether the contactor works normally.
overtravel signal
Overtravel limit switches are set on hoisting, grab bucket and luffing mechanisms, and all signals are sent to PLC. In case of overtravel signal, instructions are sent to stop corresponding mechanisms to prevent equipment damage due to runaway.
Circuit breaker and disconnector status signal
During the operation of floating crane, all circuit breakers and isolating switches are required to be in the closed position. The auxiliary contact of the switch will lead the signal into PLC. When any switch is not in the closed position, PLC will give light prompt and block the operation instruction.
instruction safety design
The instruction sent by PLC will automatically make the equipment in safe shutdown state when PLC itself fails.
4 System function design
4.1 Basic operating functions
The basic operation function is realized by toggling the key switch and the left and right two handle cam controllers.
Allow to operate the key switch
The keyswitch has three positions: Operation, grab operation and hoisting operation are prohibited. When the floating crane stops operation, the switch is set to the operation prohibition position, and all operation instructions are blocked at this time, and all operations are invalid. When preparing to start the grab operation, the key switch in the grab operation position, the operation is allowed, at the same time, corresponding to the cam controller of the gear, PLC will output to the inverter and grab operation appropriate speed instructions. When preparing to start hoisting operation, the key switch is placed in the hoisting operation position, and each operation is allowed to proceed. At the same time, corresponding to each gear of the cam controller, the PLC will output the speed instruction suitable for hoisting operation to each frequency converter.
Rotary and luffing manipulator
The manipulator is a lever cam controller. In addition to the zero position, there are three gears in the longitudinal direction, which are used to control the luffing mechanism and can move forward or backward at three speeds. There are three gears on the left and right in the horizontal direction except the zero position, which are used to control the rotating mechanism and can rotate left or right at three speeds. The manipulator can be operated obliquely, that is, it can control the luffing and rotating mechanism simultaneously. The speed of each gear can be set independently on the drive.
hoist and grab manipulator
The manipulator is a lever cam controller. In addition to zero position, there are three gears in the longitudinal direction, and there are two gears in the transverse direction, namely, middle position and right position. When the handle is in the middle position, the front and rear operating handles will simultaneously control the lifting and synchronous operation of the grab bucket motor, so as to make the grab bucket rise or fall. When the handle is in the right position, the front and rear operating handles will independently control the grab motor to open or close the grab. The speed of each gear can be set independently on the drive. 4.2 Safety interlock function
Rotating mechanism electrical fail-safe interlock
Electrical faults of rotating mechanism include rotary frequency converter fault, circuit breaker fault and disconnector failure. After the fault occurs, the PLC will send out an instruction to stop the rotating mechanism immediately. Meanwhile, the hoisting, grab bucket and luffing mechanism will slow down and stop under the control of PLC. After the shutdown, the other three mechanisms can activate the operation function by resetting the operating rod, so as to lower the grab bucket to the appropriate position for troubleshooting.
Mechanism electrical fail-safe interlock
The electrical faults of luffing mechanism include the faults of luffing frequency converter, circuit breaker, disconnector not closed and the faults reflected by differential signal of contactor. In case of failure, PLC will send out instruction to stop the luffing mechanism immediately. Meanwhile, the hoisting mechanism, grab bucket and rotating mechanism will slow down and stop under the control of PLC. After the shutdown, the other three mechanisms can activate the operation function by resetting the operating lever, so as to lower the grab bucket to the appropriate position for troubleshooting.
Electrical fault safety interlock of hoisting and grab mechanism
Electrical faults of hoisting and grab mechanism include hoisting or grab inverter fault, circuit breaker fault, disconnecting switch not closed and faults reflected by differential signal of contactor. In case of failure, PLC will issue instructions for lifting and grab mechanism to stop immediately, meanwhile, rotating and luffing mechanism will slow down and stop under the control of PLC. After shutdown, the other two mechanisms can activate the operation function by resetting the operating rod to zero, so as to move the grab to the appropriate position.
At this time, PLC will make a confirmation to allow the fault lowering operation. After the operation lowering key is turned off, the operator can step on the pedal and lower the grab by releasing the lifting and grab mechanical brakes for troubleshooting.
Safety Interlock in PLC Failure
All the equipment will stop immediately when the PLC fails, and the PLC connection logic designs that the whole system is in a safe shutdown state when the PLC fails to stop. If the PLC has an error output during a fault, an emergency stop operation can be performed immediately. 4.3 Anti-misoperation function
instant acceleration anti-misoperation
When the operator instantly pushes a mechanism from zero speed to high speed, the inverter will not respond immediately to this operation, but will increase the speed at the allowed acceleration according to the normal setting.
Quick reverse anti-misoperation
When the operator quickly switches a mechanism from high-speed operation in one direction to reverse operation, the inverter will not respond to this operation immediately, but will slow down and stop according to the normal procedure, and then start in reverse after obtaining zero-speed feedback.
Travel anti-misoperation
When the operator accidentally causes the lifting and grab bucket or luffing mechanism to exceed the normal travel, PLC will immediately send out the emergency stop instruction of the mechanism, and block the operation in this direction at the same time. The reverse direction operation will be activated when the operator returns to zero, so that the mechanism can withdraw from the overtravel position.
Moment balance function
When grab bucket is lifted, it is by rise and grab bucket motor move at the same time, but when grab bucket closes, grab bucket motor already moved ahead of schedule, bring about rise easily and grab bucket motor to bear force unbalance, grab bucket motor and steel rope are easy to be damaged, in order to solve this problem, adopt moment of force to track control mode between lifting head and grab bucket transducer, the bear force of two motors can be achieved very quickly basically consistent.
5 concluding remarks floating crane because of the bad working environment, in the design to consider the technical details of the problem is more, as long as the attention to the above-mentioned problems to do a good job of technical treatment, installation and commissioning will be much smoother, the system put into operation for a year, stable and reliable operation, praised by users.
