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AG Stabilization

MONOCAB OWL is supported by:

WG Management

  • Martin Griese

    iFE - Institute for Energy Research / Institute Future Energy. Ostwestfalen-Lippe University of Applied Sciences / OWL

Info about the Stabilization Working Group

Primary and secondary stabilization system

The stabilization working group includes the design and construction of the active primary and secondary stabilization system, with the aim of keeping the vehicle in a vertical position above the rail.
For this purpose, dynamic and stationary disturbances (wind, passengers) must be compensated and introduced angular momentum must be compensated. The compensation of dynamic, impulse-like disturbances is carried out by the gyroscopic actuator systems as a primary stabilization measure, while as a secondary measure the mechanics designed to shift the batteries compensate for stationary disturbances by shifting the vehicle's center of gravity.
The gyroscopes used for stabilization are supplemented with an active control system, which is characterized by the fact that a tilting motion of the gyro-stabilized vehicle is compensated for by suitable control of an actuator (e.g. electric servomotor) by rotating the axis of rotation of the gyroscopes in such a way that the gyro torques thus generated restore the desired vertical position of the vehicle. The necessary speed of movement of the gyro axes is calculated from the measurement of the tilting motion via a suitable sensor in the control algorithm.

 

Suitable stabilization of the vehicle on a rail requires that the vehicle's center of gravity (C.G.) is located directly above the rail and at an optimized height. This height must be determined in the project via simulations and model calculations in order to sound out a suitable compromise between sensitivity and reaction moments. The SP depends of course on the design of the vehicle (mass distribution), but also on the load or passenger distribution in the vehicle. Especially the latter aspects cannot be planned. In order to optimize gyro stabilization and thus make do with smaller gyro systems, a device for adjusting the center of gravity is additionally integrated. For this purpose, the vehicle is equipped with a displaceable mass so that the position of the center of gravity is made possible by suitable control of the displacement device. The displaceable mass is preferably provided by the vehicle battery (in the case of a battery-electric vehicle) and/or by the gyro system, both of which are heavy but compact technical components in the vehicle.

Stabilization cannot be achieved in a practical form in terms of safety and comfort either with an active gyroscope or with weight shifting as the sole stabilization system. With an exclusively active gyro stabilization system, stabilizing but limited angular momentum can be generated very quickly. If there is a stationary disturbance of the equilibrium due to crosswind or one-sided loading, this would have to be compensated by a permanent tilting (deviation from the geometric vertical position) of the vehicle. This is inadmissible for operation for the following reasons: Lack of comfort, possible collision when passing MONOCABs or at stopping points, and possible wheel-rail contact problems. Exclusive stabilization via weight shifting must also be ruled out, since this is problematic from a system/control point of view (non-minimum-phase behavior of the system), can also theoretically only function at very low center of gravity positions of the shiftable masses, and requires very powerful actuators for sufficient dynamics, which are unsuitable for vehicle operation in terms of weight, installation space and energy consumption.

The system-technical interaction of both stabilization measures is therefore required. Taking the safety concept into account, a powerful control system for the primary and secondary stabilization system must be developed which, in addition to position control, includes independent monitoring, including redundant sensors for gyro, battery and vehicle position, in order to ensure the required fail-safe behavior. In addition to the formulated goal of keeping the vertical position of the MONOCAB stable, another goal is to guide the gyro systems into the neutral position. For this control task, state control, multivariable cascade control and combinations of the two variants are conceivable. The development of the closed-loop and open-loop control system is largely model-based and is being comprehensively investigated both with simulation support and with test bench setups. This step takes place before integration into the prototypes, so that errors during development (e.g. due to disregard of non-modeled effects) can still be corrected.

For the MONOCAB, in the event of a system failure, it must be ensured that the vehicle does not tilt completely out of a tolerance range around the vertical position. System failures to be considered are events that make active stabilization via the described combined gyro and weight stabilization system impossible, such as failures of the electrical supply, the position sensors (error message/deviation of redundant sensors), the actuators, the vehicle-internal communication or the control system (deviation/error of the monitoring redundant control units). In such cases, passive stabilization can be achieved for a limited time: After system failure, the gyro(s) continue(s) to have a high rotational speed, which is reduced only very slowly in the vacuum gears. If the gyro frame(s) is/are no longer forcibly guided by an actuator but is/are placed in an unstable position by a passive mechanical device (e.g. a spring), the interaction between the vehicle and the gyro frame results in stabilization in the sense of raising the vehicle.
However, this operating state is itself unstable, since the vehicle performs an oscillation about the longitudinal axis with increasing amplitude and would finally overturn. Depending on the damping in the system, however, sufficient time remains to initiate emergency braking, extend a support system and bring the vehicle into a safe operating state.
The following components are to be developed specifically for this purpose:

  • a mechanical device (safety coupling) that decouples the moving gyro frame from its actuator and simultaneously couples it to mechanical system that applies destabilizing torque to the gyro frame,
  • an electromechanical device in which the process described above is automatically triggered, e.g. in the event of a voltage drop at an electromechanical actuator which is energized during normal operation, if the voltage supply fails or control devices trigger a deliberate shutdown (intrinsic safety),
  • an emergency procedure in which passive stabilization is used to bring the vehicle to a safe state in the event of the system failure described above,
  • an emergency support used for this purpose, which can also be activated passively in the event of system failure, i.e. without control and electrical supply, e.g. by springs or pneumatic reserve energy.

Time-limited passive stabilization can also be achieved if the circular actuator acts at the base of the instabilizing spring instead of the safety coupling (sequential arrangement).
In the event of a fault, the gyro actuator is then, depending on the type of fault, either moved to the neutral position or held passively (due to self-locking) or actively (with a separate braking device) in its instantaneous position. As an alternative concept without the installation of a gyro actuator or as an emergency control in the event of failure of the gyro actuator, stabilization can be achieved exclusively with weight shifting as the only adjustment option in the overall system. The oscillation of the passive gyro stabilization is suppressed by an angular momentum component introduced specifically by means of weight shifting.

Tertiary stabilization/support system

A mechanical support system is planned as the tertiary stabilization system for emergencies and for supporting the parked and switched-off MONOCABs. In order to be able to guarantee a fail-safe behavior of the system in any expected situation, a monitoring and control concept of various system functions must be realized. Among other things, a redundant position sensor system is planned. In the event of a failure of the control system or the electrical supply, the gyro system is to be switched to passive operation (free movement) and, in uncontrollable cases, to neutral operation (blocking). In particular, the requirements of the safety concept must be taken into account.

Integration and testing of the stabilization system

The integration of all components and testing of the stabilization system is planned for the final phase. For this purpose, among other things, a test bench is to be developed that can be used to simulate different scenarios of rail operation under the influence of external disturbances (including emergency situations).

In the test rig, the chassis is replaced by swivel joints in order to reproduce the movement of the vehicle over a virtual rail by means of an active fu point displacement. In addition to suitable linear drives, various mechanical adaptations and sufficient metrological instrumentation of the integrated components and the test rig are required (sensors for torques, forces and positions). A real-time system must be integrated to record the measured values and to control the test bench.

After initial commissioning of the stabilization system, all components in the network are to be tested during normal operation and various fault scenarios. Early tests with real components are intended to reveal possible inadequacies and errors (e.g. disregard of dominant non-modeled effects) so that any errors can be corrected in a further iteration, if necessary, before the final integration of the systems into the complete vehicle. In this way, it can be ensured with a high degree of probability that the systems will work reliably in subsequent tests with the complete vehicle and that the planned fail-safe concept will function.

The integration of all components into the frame, the construction of the test stands as well as the implementation and testing of the control technology requires competences in the fields of control engineering, mechatronics and construction. The processing is carried out in a cooperative manner by the working group of Prof. Schulte and Prof. Kiesel.

Publications

  • Georg Klepp, Guido Langer: Monorail Flow Patterns and Vehicle Drag. In: Aerovehicles 4-Fourth International Conference in Numerical and Experimental Aerodynamics of Road Vehicles and Trains, Berlin, August 2021.
  • Martin Griese, Fabian Kottmeier, Thomas Schulte: Vertical control of a self-stabilizing monorail vehicle. In: IECON 2021-47th Annual Conference of the IEEE Industrial Electronics Society. 13-16 October 2021.
  • Martin Griese, Seyed Davood Mousavi, Thomas Schulte: Modeling the vertical dynamics of a self-stabilizing monorail vehicle. In: ICCMA 2021- 9th International Conference on Control, Mechatronics and Automation. 11-14 November 2021.

The team