Konecranes World №7

More documents

Recommendations

Info

@ KONECRANES KNOW-HOW DEDICATED FEATURES IN KCI DRIVES Today’s advanced crane technology tightly integrates mechanical, electrical and controls, which makes it nearly impossible to reach a safe, reliable and optimised solution with distributed (or diverse) suppliers. The crane manufacturer who fully understands the customer’s product requirements has the best grasp of all the interactions and relations between structure and components. Integrated systems developed and applied by crane manufacturers provide additional advantages in functionality, reliability and maintainability. 16 KONECRANES’ WORLD No 7 Figure 1. Field bus configuration for Rubber Tyred Gantry crane PLC System hardware configuration Konecranes utilises the Profibus DP field bus between distributed peripherals (inverters, PLC, sensors.) A typical configuration in crane application is shown on Figure 1. Local digital and analogic sensors are connected to remote units, which transfer data through bus to PLC. The transfer means, fibre optics, provide reliable operation compared to separately wired configuration. In addition, the field bus provides advanced features for data collection and diagnostics on inverter events during operation. The information data frames, as shown on Figure 2, have been identified within the Profibus protocol depending on the content to avoid any disturbances between control and monitoring messages. While the field bus is actively utilised to change drive variables even during operation, the monitoring data is collected for maintenance and continuous product development purposes. DYNA torque control Torque control with inverter drives is by no means a new idea. However, most drives are still designed with speed reference as the only adjustable control factor, which in some cases causes problems due to rigidity of the control system. KCI has proven torque control solutions to overcome issues that arise with speed reference control systems. Torque control applications addressed by Konecranes products include: ■ Jib crane boom slew ■ Trolley free rolling ■ Grab lowering ■ Load sway control ■ Master-Slave hoisting, mechanically connected separate machineries ■ Master-Slave traversing, unbalanced load distribution with two machineries ■ Multi-motor drives with unequal loading Single drive applications Boom slewing A general problem while accelerating and decelerating large structures with high inertia is that dynamics cause deflections and vibrations. A machinery drive system with rigid speed reference cannot acknowledge the behaviour of the moved structure and tends to amplify structural resonance. An inverter with torque reference continuously controls the slewing motor. Direction and torque references are given by the cabin operator or from the control PLC. Torque reference is held posi-
tive on the motor shaft according to direction reference. The slewing motion is controlled by accelerating or decelerating torque. When the direction reference is not activated, the inverter keeps the motor magnetising on, which results in almost zero torque on the motor shaft. When a new direction and torque reference is given, the inverter is able to respond quickly and smoothly. The inverter can also control the brake, but generally this is activated by a pedal brake switch (the brake is not motor mounted.) Torque control is always activated with a steady motor (zero speed) which is achieved by holding the machinery by pedal brake, motor brake or by friction in the system. The start from zero speed enables smooth acceleration compared to a start with traditional speed reference control, which opens the brake on a certain frequency and causes additional structural vibration. Trolley free rolling Cranes with cabins and drivers onboard have specific requirements in respect to operator preference. Operators used to old-style resistor-start controls occasionally claim that the driving “touch” of the crane is not to their liking or what they are used to. It is true that inverter or PLC controls have predetermined acceleration and deceleration ramps, which do not give the operator the possibility of modifying these movements. While positioning the trolley, some operators prefer to adjust the deceleration with the controller instead of letting the control system to take over. A torque-controlled inverter continuously controls the motor with torque refer- Figure 2. Communication between PLC and inverter ence. Direction reference holds the torque positive on the motor shaft. When the direction reference is not activated, the inverter maintains the magnetising of the motor in the “on” position until a new direction and torque reference is given. The brake is closed and magnetising stopped when the actual speed is below the brake closing reference. A typical torque-controlled inverter drive system configuration is shown on Figure 3. The torque reference Tref for the controller is given by analogy input. Combinations of the torque reference and direction define the torque direction on the motor shaft: When Tref > 0 and S1 active => shaft torque to direction S1 Tref > 0 and S2 active => shaft torque to direction S2 Tref < 0 and S1 active => shaft torque to direction S2 Tref < 0 and S2 active => shaft torque to direction S1 When the direction reference is deactivated, there are three alternative stopping modes to choose from: ■ Stopping with the brake, which is activated immediately after the direction reference is disconnected. The inverter controls close the brake and the motor is de-energised. ■ Stopping with deceleration ramp, which is generated by the inverter following the closed loop speed reference deceleration ramp. ■ Stopping with free rolling, which is generated by magnetising the motor until the actual speed is below the brake closing speed. Then brake is closed and motor de-energised. During the operation, the actual torque on the motor shaft can be limited with a predetermined inverter parameter. Adjustable parameters for speed reference as well as “slow down” and “stop” limit switches are available also. Fast mode change, Grab lowering A rope-driven grab, when filling, should be lowered by the hoist machinery to provide the best charging. Once the grab is closed, the closing machinery (including the ropes) takes its share of load suspension. Without compensation, the filling ability of the grab is insufficient. A closed loop system with speed reference does not enable proper control over charging. Konecranes’ grab control software has been implemented to switch fluently from speed reference mode to torque reference mode by a digital input (part of the operator’s controller) during lowering, without stopping between the stages. Lowering of the grab is implemented so that a small predetermined constant torque reference is held on hoisting machinery, while the closing machinery closes the grab. The hoisting machinery senses the load increase (due to grab filling) and lowers the grab according to torque reference. This dual function allows the grab to maintain hoist rope tension and provide a smooth start. Continuous torque control An example of a continuous torque control application is the active sway control system in Konecranes’ Rubber Tyred Gantry crane. The loading device (spreader) is controlled by four auxiliary ropes, which are separately driven by torque-controlled drives. The control algorithms aim to equalise torques between machineries in case of sway or other disturbances. The crane’s PLC sets the torque reference according to a measured load when crane movement is activated. Each auxiliary drive system has its own PLC controller, which by adjusting the torque prevents and dampens sway. The inverter controls the brake and torque is kept on the motor until the brake is closed. Snag load protection A snag load can occur when loading or unloading cargo. The risk is that the No 7 KONECRANES’ WORLD 17
Page 1 and 2: Big Is Beautiful Goliath Gantry Cra
Page 3 and 4: Big is Beautiful Go·li·ath [ge-l
Page 5 and 6: than two months and the shipyard wa
Page 7 and 8: ment response is slow. The position
Page 9 and 10: KCI Koneports takes the lead in har
Page 11 and 12: tion. We have also just introduced
Page 13 and 14: CORPORATE NEWS CORPORATE NEWS CORPO
Page 15: VLC NEWS VLC NEWS VLC NEWS VLC NEWS
Page 19 and 20: sizes increase, DC motors are gener

Konecranes World №7

Create successful ePaper yourself

Delete template?

Save as template?