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MDA Technologies 3/2016

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MDA Technologies 3/2016

The lift and carry crane

The lift and carry crane in detail It is the Travellift’s job to pick up various workpieces, to lift them, transport and position them. The Travellift lifts the item to be transported using two winches via a crossbeam. The raised items can then be moved. Thanks to the arrangement and variable maneuverability of the wheels, the items can be maneuvered and loaded in a variety of ways. The Travellift is hydraulically powered. The hydraulic energy is generated by a diesel motor, which drives the hydraulic pumps. The Travellift’s chassis consists of four wheel units with hydraulically powered gearboxes, which are each individually maneuverable. To achieve the maximum degree of maneuverability when transporting workpieces, the Travellift has five methods of steering which can be selected via the two steering type selector switches, one installed in the driver’s cabin and one available using radio-controlled remote access. The continuous activation of the drive motor from 0 – 15 km/h is achieved thanks to an electronic accelerator pedal and direction of travel switch. Steering is activated by an electronic steering force simulator (steer-by-wire). There is, therefore, no direct Simulation of the winch control During project planning of the winch control, safe holding of the winch was simulated under real operating conditions. Automation Studio, a simulation software developed by Famic Technologies, was used to simulate the hydraulics and electrical systems. In particular, the behavior of the brakelowering valves that have been flanged on the winches’ hydraulic motors was analyzed under the following operational states: n Stop of the winches by withdrawing the control lever n Stop by control outage = Emergency Stop Category 1, no electric energy, diesel engine still running n Stop by outage of diesel engine = Emergency Stop Category 0 The most critical operation state “the Emergency Stop Category 0” will be explained in detail in the following section. mechanical connection between the steering wheel and the wheels. The steering force simulator displays the intended value for the angle of steering. A safety angle display unit is built in the center point of each wheel-bearing, which detects the actual value of the steering axis. The lift working area is divided into two lifting hoists and two traveling trolleys, which are also hydraulically powered. They are steered using a control lever in the right hand seat console. The hydraulic aggregate forms the central power supply for energy supply and the steering unit for all hydraulic and electronic users of the Travellift. Designing the hydraulic aggregate involved the most extensive work due to the complex, multiple requirements for all of the functional demands, including installation space regulations as well as fuel emissions and noise regulations. The Travellift was installed and commissioned under the management and supervision of Grunau & Schröder Maschinentechnik at Max Bögl. Following a Features of Use n Handles different shapes of structural components n High driver vehicle dynamics n Speed of travel up to 13 km/h fully loaded - 15 km/h empty n Exact and direct steering behavior n Different types of steering for maximum maneuverability n Quick but also delicate and precise control of the functions n Working capacity 16-20 hours/day n High full throttle ratio (with 3 liters) n Exhaust Emissions Guideline Level 4 final n Sound Pressure Level Lp ≤ 80 db(A) at 5 meters Removal because of neighboring housing settlements successful six-month test phase with two shifts working each day we are planning to produce further pieces of equipment. MDA Technologies 3/2016

Description of the simulation modules Figure 1 depicts the most relevant components for the simulation. All displayed components are simulated during the lifting process. The drive unit with clutch transfers the power via a transfer gear box to the lower main pump and the upper charge pump. The fluid (red line with arrows indicating flow direction) flows through the proportional valve to the brake-lowering valve module and finally to the hydraulic motor. Inside the brake-lowering module, the brake piston is driven by the load pressure and the multiple disk brake is opened via an integrated brake-discharge unit (2/2 directional valve and pressure reduction valve). The fluid in the hydraulic motor’s return line (blue line with arrows indicating flow direction) flows back via the brake piston towards the proportional valve. Thus, the load in the illustrated control mode remains hydraulically locked by the brake piston during regular operation. In Figure 2, the stop of the diesel engine and the resulting blockage of the hydraulic pumps are simulated by disconnecting the clutch. In this case, the following situations can be observed: n Because of the switched activated proportional valve, the load pressure at the brake-lowering valve remains high and is only slowly reduced through leakage (see measuring point MI-6). n Due to the high pressure, the integrated brake-discharge unit is further charged with pressure and the multiple disk brake stays open. The load is further retained by the brake piston and held on the hydraulic oil column (see measuring point MI-8). n However, by holding the load on the hydraulic oil column, a potential movement cannot be stopped completely. Due to a leakage inside the hydraulic motor, the winch is rotating at a speed that can’t be detected visually. n Without the continuous feeding of hydraulic oil through the feeding pump, the hydraulic motor cannot absorb oil during the creeping rotation and starts to cavitate. This phenomenon can be observed at measuring point MI-9 with the constantly increasing negative pressure and drive speed at the driving wheel. When reaching less than one turn during cavitation, the motor cannot keep holding the load and slips. n Furthermore, the integrated brake-discharge unit needs another 1-3 seconds to activate the multiple disk brakes with the proportional valve in neutral position (ABT connection). In the operational state, “engine stop – pilot valve still electrically operated” a time response of 6 seconds could be measured. Figure 3 shows a realistic comparison between the simulation with Automation Studio and the real measurements at the plant: n Blue line: load pressure to lift the precast element n Turquoise line: absorption of the load by brake pistons with a tendency to slip (cavitation) n Black line: delayed relief of control pressure on multiple disk brakes About Famic Technologies The portfolio of the company Famic Technologies, founded in 1986, includes high-end products and services in the field of software engineering and industrial automation. The well-known software solution Automation Studio was originally developed for training and further education purposes in the field of fluid technology and is used today all through the industry, for systems development and optimization, maintenance, services and training. 01 Simulation of the winch control MEASUREMENT AND CONTROL MDA Technologies 3/2016