Technical Review: Effective Management of Hosting and Transport Mechanisms
Algorithms for controlling hoisting and transport mechanisms are usually multitasking. They must be fast, accurate, robust and, in essence, replace the actions of trained personnel, in other words, they must have “intelligence”. Controlling system should move the load at the highest possible speed, during transportation minimize the fluctuations of the load and completely suppress them at the stopping place. Also, possible changes in the system parameters, such as cable length and cargo weight, should be taken into account. Developing control algorithms, practical implementation issues should be taken into account: control power, maximum acceleration, speed, etc. To avoid the possibility of collisions with obstacles, the cargo should not go out during transportation outside the specified corridor.
Triol AT24 VFD has special functions of lifting mechanisms: brake control, evacuation modes, inspections, short floor. Unique algorithms allow you to operate gearless winches.
The system of controlling the process of moving cargo can be either open or closed. Open control is more sensitive to changes in parameters and disturbances. When creating a closed control system, there is a need for appropriate sensors. Information on the position and speed of the trolley is usually obtained from the electric drive control system of the trolley. It is more difficult to obtain information on the angle of the deviation of the load. You can use a vision sensor, but the disadvantages of the video system are the complexity of the service and the high cost. With a known rope length, the angle of deflection can be estimated from the electromagnetic torque and angular velocity of the bogie engine, in other words, the dynamic load observer must be included in the structure of the control system.
The interaction between the movement mechanism and the suspended payload leads to the swaying of the latter. If the amplitude of the oscillations exceeds a predetermined limit, they must be suppressed or the operation must be stopped until the oscillations stop. In any case, this will lead to a deterioration in system performance. These problems have led many researchers to develop control algorithms that automate crane operations. However, most of the existing schemes are not suitable for practical applications. Therefore, a large number of industrial cranes are not automated and still depend on human actions. At the same time, only a highly qualified operator (crane operator) must ensure proper compensation of fluctuations in the state.
Triol AT24 VFD supports incremental and absolute encoders. Vector control allows working in a closed system with feedback on speed and in an open system without speed feedback.
There are various ways to control the crane, based on both the open system and the closed-loop control system. The automation of the crane can be divided into two approaches. In the first approach, the operator is stored in the control circuit, and the forces moving the load change in a certain way to facilitate the operator’s work. The one way is to add damping, closing the system by the angle of the load’s oscillations and the speed of its change. In this case, the trajectory specified by the operator is corrected. The second way is to avoid excitation of the load near its own frequency by adding a filter to remove this frequency from the input signal. This leads to a delay between the operator’s action and the input signal of the crane. This delay can confuse the operator. The third way is to add a mechanical absorber to the structure of the crane. However, the implementation of this method requires considerable power, which makes it impractical.
In the second approach, the operator is removed from the control circuit, and the move operation is performed in automatic mode. This can be done using a variety of methods. The first method is based on the formation of trajectories that allow you to move cargo to the destination with minimal swing. These trajectories are achieved either by the formation of a special input signal or by optimal control methods. The second method is based on feedback on the position and angle of the deviation of the load. The third method is based on dividing the control system into two parts: a vibration suppression controller and a position controller. Each is developed separately, and then combine to ensure the operation of the system while maintaining stability.
Triol AT24 VFD allows measuring engine parameters without rotation. The built-in “language of elevators” provides identification of the parameters: rpm, m / s.
The use of both the time-optimal open crane control system and the open control system in which the input signal is formed in such a way that when the trolley is moved to a predetermined position does not cause excessive flywheel movements of the payload, produces poor results, since the control without feedback Is sensitive to changes in the parameters of the system (for example, the length of the cable) and cannot compensate for the effect of wind. These methods also cannot prevent residual cargo fluctuations.
Control with feedback is known to be less sensitive to changes in parameters and perturbations. Therefore, in most studies of recent years, closed-loop control algorithms have been proposed: from a conventional PID controller (proportional-integral-differential controller) to intelligent approaches. In particular, the use of a PD controller (proportional differential controller) for both positioning and suppression of oscillations. However, it is known that position control using a PD controller is not effective in eliminating a static error. Therefore, a PID controller was also proposed to operate the portal crane system. However, the operation of the regulator deteriorates when the power drive is saturated.
Adjustment of the cycle of variable frequency drives Triol AT24 is carried out through automatic control of technological processes on the principle of a closed system with the built-in PID controller.
For the construction of traditional regulators, it is necessary to have an “accurate” mathematical model of the control object, and then to synthesize the controller that implements the necessary control algorithm. Since the mathematical description of the crane is a system of non-linear non-stationary differential equations, it is difficult to perform the synthesis of the regulator analytically, this problem can be solved only for small angles of deviation of the load by linearizing the corresponding equations and “Freezing” of their coefficients. For systems of this type, the use of non-traditional controllers is preferred. As you know, to manage complex processes, when there is no simple mathematical model, you can use systems with fuzzy control.
The control methods discussed above would lead to good work, provided that the exact model and its parameters are used in the regulator. However, it is known that modelling is complex and time-consuming. In addition, it is required to identify those crane parameters that cannot be measured. Identifying parameters is also a complex and time-consuming process. In addition, advanced regulators tend to be increasingly complex and, accordingly, problematic from the point of view of their implementation in real time. Very often, such adjustments should be set by engineers who have no experience in working with similar control systems. Consequently, the simple design and structure of the regulator are very important from a practical point of view.
Variable frequency drives Triol AT24 has a high overload capacity of 220% for 1 to 2 seconds and 150% for 60 seconds. The drive is developed on the basis of modern technologies and allows easy control of asynchronous and ventilated motors of elevators and lifting mechanisms.
The disadvantage of closed systems is the need for sensors for the position of the trolley and the angle of deflection of the load. In addition, the creation of a vibration measurement sensor in a real portal crane system is not an easy task, since there is a lifting mechanism on a parallel flexible suspension. In some studies, we focused on control schemes with a video system, which in practice found more use in view of the fact that it is not necessary to locate the sensor on the load side. Disadvantages of feedback control based on a CCD camera (vision sensor) are the complexity of maintenance and high cost.
In the cases under consideration, it is advisable to use a technique based on measuring the electromagnetic torque and the angular velocity of the engine and using the dynamic load observer. This method allows you to estimate the angle of the load deviation from the information available from the power drive and does not require the use of expensive and technically complex sensors.
Application of the developed algorithms in cranes leads to the following improvements:
- Reduction of the time of loading and unloading operations due to the exclusion of time to calm the cargo;
- Improving the safety of the crane when transporting goods near obstacles; Reducing the fatigue of the crane operator due to the elimination of the need to perform additional manoeuvres and pay increased attention to tracking the load;
- As an additional effect – reduced energy consumption due to the elimination of energy costs for the formation of oscillations and the elimination of unnecessary movements during manoeuvring.
The expected effect from the application of the developed algorithms is to reduce the time spent during the transportation of goods in the workshops, during construction, loading / unloading of ships, etc., as well as in the creation of high-precision positioning systems for process equipment for the installation of turbines and generators of power plants, Bolts, etc. The developed algorithms will be in demand in the development of liquid metal filling systems at metallurgical plants, cargo (container) loading and unloading systems at modern container terminals, drive control systems for construction cranes providing (increasing) their safety in high-rise construction, control systems for industrial cranes At factories, loading and unloading hazardous materials at nuclear facilities.
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