Abstract: Cranes have become an indispensable piece of equipment for many enterprises, serving as crucial tools for achieving mechanization and automation in production processes, reducing heavy manual labor, improving production efficiency, and ensuring safe production. Consequently, with technological advancements, innovations, and the specific requirements of cranes themselves, a wide variety of transmission control systems have emerged, resulting in diverse control methods and schemes. Keywords: crane; transmission control system; control method; control scheme [b][align=center]The crane's drive to control a variety of techniques XU Wei-Feng[/align][/b] Abstract: Cranes have become indispensable for many businesses, as they realize the mechanization and automation of the production process, reducing heavy manual labor, increasing productivity, and ensuring safe production of major equipment. The crane's control system also drives technological development and innovation, as well as meeting the requirements and characteristics of cranes. Therefore, there is a wide range of transmission control systems, which control various modes and programs to manage the crane's movement. Key words: crane; control system; control transmission; control of the program I. Overview A crane is a lifting machine that enables the lifting, lowering, and horizontal displacement of heavy objects suspended on hooks or other lifting devices in three-dimensional space. The lifting and movement of the heavy objects are achieved by the crane's transmission control system driving various transmission mechanisms. The crane's transmission control system mainly includes transmission control methods and transmission control schemes. Generally, the control method and scheme of any transmission control system must be designed according to the load characteristics, operating conditions, and speed regulation requirements of each transmission mechanism of the crane. Therefore, the transmission control system of bridge cranes (hereinafter referred to as cranes) has a variety of control methods and schemes. II. Transmission Control Methods of Cranes The transmission control method of a crane is generally selected according to the requirements of the crane's transmission control system for operational performance and methods, as well as the form and location of the operating device. Its control methods mainly adopt operator cab control, ground wired control, and wireless control. 1. Operator Cab Control Method The operator cab control method allows the operator to control the starting, speed regulation, braking, and reversing of the motors of each transmission mechanism of the crane through control components in the operator cab, realizing the lifting and moving of heavy objects. The operator cab control method generally has four main control components: push-button control box, cam controller, linkage controller, and industrial computer. 1) The control panel of the push-button control box is equipped with control buttons, control switches, and indicator lights, etc., which can control the crane independently or in conjunction with the cam controller or linkage controller to control the crane. 2) A cam controller is a control device that controls the starting, speed regulation, braking, and reversing of a motor by switching the wiring of the main circuit and control circuit and changing the parameters in the circuit according to a predetermined sequence. The cam controller consists of three parts: the operating mechanism, the cam and contact system, and the housing. Its operating handle is equipped with a zero-position self-locking device to prevent malfunctions caused by crane vibration and accidental collisions. However, one cam controller can generally only control one or two transmission mechanisms with the same function. Therefore, when controlling three or more transmission mechanisms, multiple cam controllers are needed to control the crane's various transmission mechanisms, making operation complex and prone to operator fatigue. 3) A linkage controller, based on the operating principle of the cam controller, improves operation by concentrating the control of each transmission mechanism into the left and right control boxes of the linkage controller according to ergonomic principles. The operation of each transmission mechanism of the crane is achieved through the linkage control handle, and linkage operation of two transmission mechanisms can also be achieved. Simultaneously, the control panels of the left and right control boxes of the linkage controller can also be equipped with control buttons, control switches, and indicator lights, which can be combined with the linkage control handle for control. 4) Industrial computers are a new type of control method used for advanced control schemes (such as control schemes combining frequency conversion technology and PLC control technology). They remotely control the control system through computer hardware and software and computer networks. However, due to the special nature of cranes and the limitations imposed by environmental and vibration conditions, the requirements for the use of industrial computers are very strict. 2. Ground-based controlled system: The ground-based controlled system involves operators controlling the crane's suspended control device via buttons, switches, and other operating elements from the ground. Signal transmission through a suspended communication cable controls the starting, speed regulation, braking, and reversing of the motors in each transmission mechanism of the crane, realizing the action of all transmission mechanisms. However, the power supply in the ground-based controlled system should not exceed 250V. The casing of the control device should be made of fully insulated material or material with an insulating protective layer. Metal casings or directly touchable metal parts must be grounded separately. The suspended control device should have effective initial suspension load to prevent cable tension during suspension. For cranes using the ground-based controlled system, there are strict requirements on the speed of the crane's trolley and crane travel mechanisms; the no-load speed should not exceed 50m/min to ensure operator safety. 3. Wireless Control Method: Wireless control refers to the method of remotely controlling mechanical equipment across a spatial distance without using conductors such as communication cables for signal transmission. Instead, it utilizes channels such as radio waves and infrared light. The control devices for wireless control are mainly divided into infrared remote control and radio remote control devices, with radio remote control devices being more commonly used in cranes. Wireless control of cranes offers advantages such as saving manpower, improving work efficiency, and increasing operational accuracy. This is especially beneficial for cranes operating in environments with toxic gases, high temperatures, high dust levels, and other hazardous conditions, significantly improving working conditions and effectively protecting personal safety. However, the wireless remote control device used in crane wireless control must have self-diagnostic capabilities, automatically shutting down and stopping operation under any abnormal working conditions; it must also be able to resist interference signals from the same frequency, preventing malfunctions when subjected to interference; and it must simultaneously meet the requirements of relevant national and international safety regulations. 4. Multi-point Control Method: Due to varying requirements for crane operation performance and methods, different operating environments, and considerations for redundant control, multi-point control methods are often required for cranes. Multi-point control of the crane can be achieved by combining operational control with wired ground control, wired ground control with wireless control, or a combination of all three methods. However, when using multi-point control, it is crucial that the control methods are interlocked, allowing only one method to operate at any given time, and each method should be equipped with an emergency power-off device. III. Crane Transmission Control Scheme The control scheme in the crane transmission control system is designed based on the characteristics of the load, working conditions, and speed regulation requirements of each transmission mechanism. The most critical aspect is the speed regulation control design. Crane control schemes can be divided into DC drive control schemes and AC drive control schemes. Currently, cranes commonly use AC drive control schemes, with DC drive control schemes only used for special requirements or when only DC power is available. 1. Crane AC Drive Control Scheme Currently, the motors in the AC drive mechanisms of cranes generally use three-phase asynchronous motors. Based on the control principle of three-phase asynchronous motors, speed regulation can be achieved by changing the number of pole pairs, the slip rate, or the power supply frequency to meet the crane transmission control requirements. Therefore, AC drive control schemes for cranes generally employ pole-changing control, slip control, and frequency conversion control. 1) Pole-changing control scheme: Pole-changing control refers to changing the connection between the stator winding coils of the crane drive mechanism motor, thereby changing the number of pole pairs and achieving speed control. This control scheme is usually only applicable when the crane drive mechanism motor is a squirrel-cage motor. 2) Slip control scheme: Due to the diverse working principles of slip control, crane drive control schemes include rotor external resistance control, stator voltage regulation control, thyristor cascade control, and synthetic characteristic control. Rotor external resistance control is the simplest scheme and was commonly used in past crane drive control, but it is the worst among slip control schemes due to high energy consumption, small speed range, poor performance, and low power factor. Stator voltage regulation control refers to changing the electromagnetic torque by adjusting the motor stator voltage, which can change the motor speed under a certain load torque, thus satisfying the control requirements of the crane drive mechanism. This control scheme typically employs methods such as connecting adjustable impedances in series with the stator windings, connecting autotransformers in series, and connecting thyristor voltage regulators in series. Currently, stator voltage regulation control for cranes commonly uses stator-connected thyristor voltage regulators because this method has simple main wiring, fewer components, and reliable performance. However, the stator voltage regulation control scheme has a limited speed regulation range, and the losses caused by speed regulation increase as the speed decreases. Therefore, it is only suitable for loads with low speed regulation requirements and infrequent low-speed operation. The thyristor cascade control scheme is the most efficient among variable slip control schemes. It can feed slip energy back to the grid and is suitable for applications with long low-speed operation times and where the low-speed value needs adjustment. Its working principle involves applying an additional electromotive force to the rotor windings of an AC winding asynchronous motor, and adjusting the value of the additional electromotive force to regulate the motor speed. However, this control scheme has disadvantages: the inverter and other auxiliary equipment are complex, maintenance is inconvenient, and when used in hoisting mechanisms, the circuits for no-load descent differ from those for medium and heavy-load descent, causing inconvenience in use. Synthetic characteristic control schemes can also be divided into dual-motor control, hydraulic actuator control, and eddy current brake control. The characteristics of this control scheme consist of two parts: the transmission mechanism motor in electric mode and the eddy current brake (which can also be a motor or hydraulic actuator) in braking mode. When controlling speed, the output torque of the motor in electric mode remains approximately constant for different loads. Under full load, the braking torque of the braking part is smaller, while under light load, the braking torque is larger. Therefore, under light load, the motor loss in electric mode is similar to that under full load, and combined with the braking loss of the braking part, the efficiency is the lowest. Among synthetic characteristics, eddy current brake control is more commonly used, followed by hydraulic actuator control. 3) Variable Frequency Control Scheme: The variable frequency control scheme refers to adjusting the synchronous speed of the motor by changing the power supply frequency through a frequency converter, achieving constant power or constant torque speed control to adapt to different load requirements. However, when the power supply frequency f varies within a range less than the motor's rated operating frequency, the motor voltage (where E1 is the induced electromotive force, f is the power supply frequency, w is the number of turns in series, k is the winding coefficient, and φ is the motor's magnetic flux) can only be maintained if U/f remains constant to ensure that the motor's magnetic flux φ remains constant and the motor's performance remains unchanged. When the power supply frequency f is greater than the motor's rated operating frequency, the motor speed exceeds the rated speed. If U/f is still maintained as constant, the terminal voltage U will exceed the motor's rated voltage, which is unacceptable. Therefore, when achieving speed regulation above the rated speed, the power supply voltage should be kept constant and at its rated value. Only by increasing the power supply frequency f, the motor's magnetic flux φ will decrease, and the output torque will also decrease accordingly, while the output power will remain approximately constant. In frequency conversion control schemes, the control modes of the frequency converters used include V/f coordinated control, slip frequency control, vector control, and direct torque control. There are several ways to classify frequency converters. According to the main circuit operating mode, they can be divided into voltage-type frequency converters and current-type frequency converters; according to the switching method, they can be divided into PAM control frequency converters, PWM control frequency converters, and high-carrier-frequency PWM control frequency converters; according to their application, they can be divided into general-purpose frequency converters, high-performance special-purpose frequency converters, high-frequency frequency converters, single-phase frequency converters, and three-phase frequency converters, etc. Frequency conversion control schemes are currently the best control scheme for cranes due to their advantages such as high efficiency, wide speed control range, high control accuracy, smooth starting/braking with low impact, high motor power factor, and energy saving. However, to prevent interference from external sources and for self-protection, as well as to improve the accuracy of motor control, AC/DC reactors, braking units and braking resistors, filters, and transmission cards are generally installed around the frequency converter. Meanwhile, frequency conversion control technology can be combined with new PLC control technology, employing fieldbus or industrial Ethernet and wireless communication technologies. Through human-machine interfaces (such as touchscreens), it can promptly reflect the crane's operating status and fault alarms, making the control system reliable, stable, flexible in application, simple in circuitry, low in failure rate, and easy to use. IV. Conclusion With the development of science and technology and technological innovation, crane control technology will accelerate its development into fields such as computers, microelectronics, automatic control, and communications, ultimately reaching a leading level compared to advanced foreign countries. Consequently, crane transmission control methods and schemes will develop towards newer and better trends, making the entire transmission control system more reliable and stable, more flexible in application, and offering advantages such as high efficiency and low failure rate. References: 1. Qiu Weizhang (ed.), Practical Handbook of Electrical Technology for Cranes, Machinery Industry Press, 2001. 2. Zhang Zhiwen et al. (eds.), Crane Design Handbook, China Railway Publishing House, 1998. 3. GB/T3811-2008 Crane Design Code, China Standards Press, 2008. 4. Dai Guangping (ed.), Electric Motors, Frequency Converters and Electric Drives, China Petrochemical Press, 1999. 5. Wang Zhengmao et al. (eds.), Electrical Machines, Xi'an Jiaotong University Press, 2000.