MMD

MMD is a measuring undercarriage built to order. We design the frame, the wheels and the sensors for the customer's vehicle and network, integrate the undercarriage with the vehicle and deliver the software with it: Krab OnBoard drives the measurement on board, KRAB 11 evaluates the files in the office. Custom projects of this kind are part of what KZV does; the mechanics, the sensors and the software come from one workshop, so they are designed to work together.

The measurement is hybrid: gauge and twist (the short-wave part of cant) are measured by contact wheels, alignment and top come from an inertial measurement unit (IMU). The original MMD measured everything by contact; the IMU was added later because the alignment from the contact chord kept a small offset that could not be calibrated away, and because the IMU resolves the long wavelengths (D2) better. The measuring chord still records alignment and top by contact, so the two can be compared as a check on each other. The undercarriage measures at ~40 km/h under the weight of the vehicle, which is what sets it apart from a hand-pushed trolley.

Three MMDs have been built so far. The Czech MMD01 and MMD02 are small measuring cars with the undercarriage integrated: a 3-axle bogie with six measuring wheels on an asymmetrical ~3 m chord, a self-contained measuring unit to which the car provides movement, power and a working area only. The newest one, delivered for MerMec in Finland, sits under a flat wagon that carries MerMec's cabin with the computers, pneumatics and power supply; the wagon is towed by MerMec's large measuring car or by a smaller vehicle, and the undercarriage is designed for Finnish winter conditions. The measured quantities and specifications below are those of the Czech MMD; yours would be defined with you.

• Under-load measurement — ~40 km/h under vehicle weight, not trolley speed
• Hybrid measurement — gauge and twist by contact, alignment and top from the IMU, with the chord measurement of alignment and top kept as a check
• Built for your vehicle — independent measuring frame designed for the host vehicle and the network
• Live on board — Krab OnBoard shows geometry graphs and values during the run; KRAB 11 evaluates the files in the office
• Shock absorbers — smooth crossover passage with dampers
• Automatic safety — bogie lifts automatically when rail contact is lost
• Optional: rail corrugation measurement