M.Sc. Martin Griese
iFE - Institute for Energy Research / Institute Future Energy. Ostwestfalen-Lippe University of Applied Sciences / OWL
Management, overall concept, design and stabilization control
1. stabilization systems
The stabilization working group includes the development, setup and commissioning of the active stabilization system, with the aim of keeping the vehicle in a vertical position above the rail. The stabilization system must be able to compensate for both dynamic and stationary disturbances.
The stabilization system is composed of the primary, secondary and tertiary subsystems. A gyroscopic system is used as the primary stabilization system, which compensates for dynamic and jump-like disturbances, while the secondary stabilization system compensates for stationary disturbances with the aid of a displaceable mass.
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. Stabilization exclusively by means of a weight shift can also be ruled out, since a movement of the mass always entails a reaction effect that is opposite to the desired compensation moment.
In addition to the two systems already mentioned for stabilizing the vertical position, four supports can be extended when the MONOCAB is stationary in order to stabilize the vehicle, for example, when parking or in the event of a fault. The mechanical support represents the tertiary stabilization system.
The various stabilization systems are shown schematically in Figure 1.1. In addition to the three systems, active stabilization control requires sensors to detect the vehicle's position and movement. For this purpose, so-called IMU sensors are used, which consist of acceleration and angular rate sensors. A sensor fusion allows precise and dynamic detection of the roll angle relevant here. The evaluation of the sensors, the control of the actuators and the regulation and control technology are implemented on two redundant control units. If, for example, one control unit fails, the second control unit can take over until a safe standstill is reached.
Figure 1.1 Illustration of the MonoCab with the three stabilizing units
1.1 Primary stabilization
In the MONOCAB, two gyroscopes, each weighing 250 kg and rotating at 4800 rpm, serve as actuators. They can be used to generate torque about the rolling axis of the vehicle by forced rotation about the precession axis. The two gyroscopes operate with opposite rotation as well as opposite precession motion. This makes it possible to compensate for externally forced movements, which is important, for example, when driving in curves. In the event of a system failure, the gyroscopes prevent the vehicle from tipping over immediately. The high angular momentum is maintained for several minutes to hours. To take advantage of the passive interaction between the pendulum motion of the vehicle and the gyro system, a reduction in friction is required. This can be achieved by disengaging the gyro precession from its actuator system in combination with a passive mechanical device. This operating state is characterized by a slowly decaying pendulum motion of the vehicle, i.e. it is itself unstable. Depending on the damping in the system, however, sufficient time remains to initiate emergency braking, extend the support system and thus bring the vehicle into a safe operating state.
Figure 1.2 shows the structure of this stabilization system. The gyroscopes are purchased as the basic unit itself from the boat sector. The company Quick (Italy) manufactures gyro systems with their own actuators, which are used to dampen the rolling motion of boats and yachts. Here, the axis of rotation of the gyros is perpendicular to the direction of travel and can be changed by an inverter-fed servo motor. The rates of change of the precession angle are comparatively low, so that a reduction is useful. In the current state of development, a bevel gear motor is used for this purpose. The motor is connected to the gyro axes via a drive chain and pinion.
To create the desired passive state in the event of a fault, the gyro mechanism can be released from the actuator system via a switchable coupling. The passive precession movement is amplified by a spring and brought into the desired unstable position. In addition to detecting the gyro position via an encoder on the motor, an encoder on a chain sprocket is integrated as a partially redundant sensor system. In terms of functional safety, slippage of the mechanical drive train can be detected, for example.
Figure 1.2 Illustration of the primary stabilization system
1.2 Secondary stabilization
As a secondary stabilization system, a so-called stabilizing mass can be shifted laterally in the vehicle to shift the center of gravity of the monorail vehicle. By shifting the center of gravity, stationary disturbances, such as uneven loading of the vehicle, can be compensated. The desired compensation torque is proportional to the lateral displacement, while a torque always occurs as a reaction effect when the mass is accelerated. The latter is opposite to the balancing torque and thus undesirable. This effect is referred to in systems theory as non-minimum phase behavior.
Figure 1.3 shows the structure of this stabilization system. The displaceable block is largely made of lead in order to obtain a high mass with compact dimensions at the same time. In the current state of development, the stabilizing mass has a weight of about 600 kg. The stabilizing mass can be moved by an inverter-fed servo motor. To translate the rotatory motor movement into a translatory displacement, a ball screw is used, which is connected to the motor via a belt. In addition to the detection of the mass position via an absolute encoder on the motor, a draw-wire sensor is integrated as a redundant sensor system. In terms of functional safety, faults in the encoder system can be detected, for example.
Figure 1.3 Schematic representation of the stabilizing mass
1.3 Tertiary stabilization
As a tertiary stabilization system for emergencies and for supporting the parked and switched-off MONOCABs, a system has been developed that provides mechanical support in the track bed. For this purpose, four supports positioned in the corners of the MONOCAB can be extended. In addition to these functions, the four supports can be used to fully jack up the vehicle, which in the current state of development is required for track mounting and dismounting (test operation) as well as for maintenance work.
Figure 1.4 shows the structure of this stabilizing system. A commercially available prop with a hand crank from the commercial vehicle segment is used as the basic unit. This has been modified as part of the project in such a way that the original hand crank is replaced by an electric motor. A hand crank can be plugged onto the shaft for manual operation.
Figure 1.4 Schematic representation of the tertiary stabilization system
2. other devices and test benches
2.1 Safety gear
During the test phase of the project, the MONOCAB is mechanically secured against tipping over by a safety gear. The safety gear prevents the vehicle from tipping over out of a tolerance range of ± 4 ° around the rest position. Figure 2.1 shows the structure of the safety gear. It consists of a trolley with a lift-off safety device, which travels parallel to the MONOCAB on the other rail. The trolley is connected to the frame of the vehicle by a telescopic device with integrated dampers. In the range of ± 4 ° around the vertical rest position, the telescopic device has only a slight influence on the stabilization behavior of the MONOCAB. Outside this range, the vehicle is prevented from tipping over.
Figure 2.1 Schematic illustration of the safety gear
2.2 Footpoint excitation
A vertical test rig was set up to analyze the stabilization of the MONOCAB. This is characterized in such a way that the contact point of the rear wheel can be shifted laterally by shifting the footing point. This allows relevant track position errors to be simulated approximately and test signals to be connected for modal analyses. The foot point displacement is implemented via an electric drive with spindle.
Publications
- Griese, M., Kottmeier, F., Schulte, T.: Vertical control of a self-stabilizing monorail vehicle. In IECON 2021-47th Annual Conference of the IEEE Industrial Electronics Society (pp. 1-6), IEEE, 2021.
- Griese, M., Mousavi, S. D., Schulte, T.: Modeling the Vertical Dynamics of a Self-stabilizing Monorail Vehicle. In 2021 9th International Conference on Control, Mechatronics and Automation (ICCMA) (pp. 205-210). IEEE, 2021.
- Klepp, G., Langer, G.: 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.
- Stork, D., Lück, S., Griese, M., Naumann, R., Schulte, T.: MonoCab - Simulation-based development of a running gear concept for monorail vehicles. In WCRR 2022-World Congress on Railway Research 2022.
- Griese, M., Mousavi, S. D., Schulte, T.: HIL simulation of a self-stabilizing monorail vehicle. In IECON 2022-48th Annual Conference of the IEEE Industrial Electronics Society, IEEE, 2022.
The team
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Patrick Döding (Research Assistant)
Conceptual design, layout and construction of the stabilization systems and auxiliary devices
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Clemens Kregel (Research Associate)
Conceptual design, layout and construction of the vehicle frame and auxiliary devices
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Fabian Kottmeier (Research Assistant)
Overall concept
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Maik Staffeldt (Research Assistant)
Support in construction, electrical planning and installation
