Solid technical skills as a success factor: system approach and anticipating challenges
Bosch Rexroth engineers went beyond simply building according to the rough design provisions set forth in the specifications; they provided critical support for the overall approach of the system, including:
- Understand the static and dynamic behavior of the entire system in its different phases of operation,
- Optimize the equipment’s energy consumption,
- Optimize power consumption peaks,
- Develop equipment control and monitoring strategies,
- Function of the elevator assembly and timing, taking account of the impact on the passenger experience,
- Optimize system controllers,
- Plan and implement redundancy in the hydraulic system and specify self-test sequences in operation, to maximize the availability of the equipment.
Anticipate challenges through smart use of digital simulations tool
What are the digital simulations used for?
An important element of Bosch Rexroth’s system approach is the use of digital simulations to verify, with a computer-based digital model, the static and dynamic behavior of a complete system, to confirm that it is properly designed, well before production.
Digital simulations for the Eiffel Tower project
As part of the Eiffel Tower project, a digital model including the hydraulics, mechanics and the control system was created:
- Model of the mechanical part: created in ADAMS.MSC 2003© by DEP Engineering Company,
- Model of the hydraulics and the control system created in MOSIHS (Bosch Rexroth development),
- Coupling and operation of the two models produced by Bosch Rexroth.
Through this model, it was possible to simulate selected operational scenarios and to verify the overall behavior of the system in ascent and descent, with changes in on-board weight, for example.
Several points are analyzed, including:
- System parameters, pressures, flow rates at various points of the circuit, power/torque required for the electric motors, maximum displacement of the hydraulic pumps, overall pressure drops in the hydraulic system, effects on hydraulic actuators, positions, speeds, accelerations of the hydraulic cylinders and the elevator cabins,
- Research and optimize controllers to control the position/speed/acceleration of the cabins, taking account of the significant elasticity effects resulting from the cables of the mechanics and the fluid columns in the hydraulic system, and check for proper control of the entire assembly,
- Simulate the overall behavior with different sampling frequencies of the control system and various resolutions of the measurement systems,
- Simulate the behavior of the assembly under the effects of faults or disturbances (e.g., carriage friction, internal friction of the hydraulic actuators, obstacles/imperfections on the rails of the hoisting trolleys, etc.).
Before the first element is manufactured, these system factors are addressed:
- Confirm the correct sizing of the equipment and its proper interaction,
- Define the equipment control strategies regarding the servo control of the main positioning/speed setting assembly of the cabins, which facilitates and therefore enables subsequent commissioning to be significantly accelerated,
- Understand and detail the influence of the different elements in the composition of the system and overall system behavior, and identify potentially critical parameters, thus enabling:
- Documentation of specifications for the subsystems concerned (e.g., minimum resolution of measurement systems, maximum permissible internal friction for actuators, max thresholds of detection of defects in operation, etc.)
- The definition and provisional implementation of counter-measures seeking to process, later, if necessary, difficulties that might arise in the equipment commissioning phase.
The benefit of simulation: ACHIEVING HIGH-QUALITY ENGINEERING
Example: the cabin leveling function
The leveling function is used to hold the cabin on the floor while the passengers enter and leave, in such a way as to avoid creating a step that would be an obstacle affecting accessibility for people with reduced mobility and, more generally, for comfortable use of the elevator. Indeed, variations in cabin payload cause variations in the length of the supporting cables and consequently a parasitic ascent or descent of the cabin that may reach several tens of centimeters. This phenomenon is observed on all cable systems but is particularly noticeable on the elevator of the Eiffel Tower because of the exceptional length of the cables: 400 meters.
This feature was the subject of very particular attention, including the use of digital simulations.
In the same way as for the coupled simulations of the overall system, these simulations were also used to check the correct static and dynamic sizing of the leveling systems. Simulations also enabled the definition, validation and pre-optimization of a very specific closed-loop control principle in cabin position on the floors while passengers are entering/leaving the cabins, taking account of the whole dynamic system involved.
They were also used to highlight the critical parameters of the installation (e.g., internal friction, stiffness of the cables, etc.) and to set up provisional counter-measures to be implemented in the event of difficulties in final commissioning.