Overview

Mine hoist is an important equipment in the production process of coal mines and non-ferrous metal mines. The safe and reliable operation of the hoist is directly related to the production status and economic benefits of the enterprise. This kind of dragging system requires frequent forward and reverse motor starting, deceleration and braking, which is a typical frictional load, i.e. constant torque characteristic load. Previously, mainly within the gear winch (mechanical drag), hydraulic winch (hydraulic drag) and AC asynchronous motor rotor series resistance speed control winch (electrical drag) and other types of dominant. The power of the inclined shaft hoist is provided by the wire-wound motor, which uses the rotor series resistance speed regulation.

The mechanical structure of the inclined shaft hoist is schematically shown in the following figure.  

At present, most small and medium-sized mines use inclined shaft winch to hoist, and the traditional inclined shaft hoist generally adopts AC winding type motor series resistance speed control system, and the resistance is controlled by AC contactor- thyristor. This control system is easy to oxidize the main contacts of the AC contactor and cause equipment failure due to the frequent action of the AC contactor during the speed regulation process and the long operation time of the equipment. In addition, the speed control performance of the hoist in the deceleration and crawling stage is poor, often resulting in inaccurate stopping position. The frequent starting, speed regulation and braking of the hoist generates considerable power consumption in the rotor external circuit of the series resistor. This AC winding motor series resistance speed control system is a step speed control, speed control of the smoothness is poor; low speed mechanical characteristics of the soft, static difference rate is large; resistance on the consumption of the differential power, energy saving is poor; starting process and speed shifting process current impact is large; high speed operation vibration, safety is poor. Therefore, the original system in the safety and reliability, speed regulation, energy saving, operation, maintenance and other aspects have different degrees of defects. Since the inverter winch, so that the equipment level of the slope winch has changed qualitatively. At present, the frequency conversion winch has become the dominant product in the market, and its main features are as follows.

1. Compact structure, small size, easy to move, used in underground mines can save a lot of development costs.
   
2. ZF series frequency conversion winch is based on full digital frequency conversion speed control and vector control technology as the core, so that the speed control performance of asynchronous motor can be comparable to that of DC motor. The performance of low frequency torque, smooth speed regulation, wide range of speed regulation, high precision, energy saving, etc.
   
3. Double PLC control system is adopted to improve the control performance and safety performance of the inclined shaft winch.
   
4. Simple operation, safe and stable operation, low failure rate, and basically maintenance-free.
   

Inverter system composition

To overcome the shortcomings of the traditional AC winding motor series resistance speed control system, the use of frequency conversion speed control technology to transform the hoist, you can achieve the full frequency (0 ~ 50 Hz) range of constant torque control. The treatment of regenerative energy, can be used inexpensive energy braking program or energy-saving more significant feed-back braking program. And in the design process of the hydraulic mechanical braking, secondary brake valve and inverter braking to be integrated. 

Inverter winch electric control system for single or double drum winding winches driven by AC asynchronous motors (wire-wound or squirrel-cage type). Can be used with the newly installed winches, but also suitable for the technical transformation of the old winch electrical control system.

Frequency conversion winch electric control system can be simply divided into: frequency conversion speed control system (frequency converter + brake unit + brake resistor box); PLC control system driver's desk.

Winch mechanical system composition as shown in Figure.

System features

Two-wire system: The PLC control system consists of two main PLC systems, PLC1 as the main control system and PLC2 as the monitoring system. Each PLC system has its own independent position detection element (shaft encoder). During normal operation, the two PLC systems are put into operation at the same time to realize the "two-wire system" control and protection of the winch. In order to ensure that the two PLC systems can work synchronously, the position and speed signals of the two PLC systems are compared in real time within PLC1, and once the deviation is too large, an alarm will be immediately generated. The two PLC systems mainly exchange data in the way of communication.

Emergency mode: If one PLC fails or its position detection element fails, the single PLC can continue to work in the "Emergency 1" or "Emergency 2" mode. Winch in the emergency mode of work, due to the protection is not missing, but no "two-wire system". However, in order to ensure the safety and reliability of the winch operation, the operating speed is reduced to half speed. If two sets of position detection elements fail, the winch can only run at a speed of no more than 0.5m / s.

Dual speed sources: The actual speed in the control system comes from two different speed sources, the inverter and the shaft encoder, and the actual speed involved in the control and overspeed protection is taken from the maximum value of both.

Position control: PLC automatically generates the speed given by the stroke as the independent variable v(s), and the speed given by the equal speed section after the implementation of v(t) and v(s) double giving, in both of which v(s) is mainly given by the stroke.

Semi-automatic operation mode: Different from the traditional semi-automatic operation mode, it uses the "speed selector switch" on the driver's console to control the running speed of the winch and the opening and closing of the working gate at the same time, which is especially suitable for the operation of the inclined shaft winch.

Lifter working process 

After the hoist is transformed by frequency conversion, the working process of the system does not change much. When pushing the handle forward and backward, it can drive the encoder to rotate and send the pulse number to the PLC high-speed counting terminal, which can steplessly adjust the speed of the inverter within a certain range. It can also give "handle zero", "forward" and "reverse" contacts. No matter the motor is forward or reverse, the coal is dragged from the mine to the ground, the motor works in forward and reverse electric state, only when the fully loaded trailer is close to the mouth of the shaft, it needs to decelerate and brake, the hoist working timing diagram is shown in the figure below.