Rising to the challenge with a customised crane drive synchronisation

Leading overhead crane supplier Modular Cranes was approached with an unusual problem. The client, a manufacturer of heavy truck trailers, had been successfully using two 22-metre-wide overhead cranes in its factory. The cranes, traditional single-girder bridge designs rated at 12.5 tonnes each, were installed on the same set of support beams spanning the entire length of the factory.

After years of reliable service, the cranes were almost at the end of their life span. However, these specific cranes are no longer in production. The client gave Modular Cranes a very clear brief: find a practical and economical alternative design solution to match the performance and synchronisation characteristics of the existing on-site cranes.

The end user, a manufacturer of heavy truck trailers, required an additional crane for the handling of new, larger trailer models.

To develop the new overhead crane’s two bridge drives, Modular Cranes consulted German drive manufacturer NORD Drivesystems.

“We were faced with the problem that our new crane needed to travel exactly in sync with the existing on-site cranes. NORD Drivesystems offered us a solution that met our customer’s budgetary requirements and assured us that we could match acceleration, deceleration, braking and traversing speeds with the existing non-inverter-driven cranes,” said Annie McDiarmid, operations manager at Modular Cranes.

NORD proposed an integrated solution consisting of an efficient helical gear unit, a standard four-pole electric motor with a 10 Nm electromagnetic brake and a motor-mounted frequency inverter with an external brake resistor. The two bridge drives were configured to synchronise and match the existing cranes using a simple parameter set-up procedure and were flange-mounted on the crane girder.

The 22 m-wide overhead cranes run on beams that span the entire length of the factory. All three are synchronised for speed and ramp times.

The crane is easily operated with the same remote control pendant, with no additional configuration required. The new crane was able to be synchronised with the existing cranes without rotary encoders due to the precision of the NORD helical gear set and the flexibility of the decentralised frequency inverter software.

NORD configured the gear units using its UNICASE helical inline gearbox series which enables flexibility in the configuration of the optimal drive train for any task and mechanical set-up by providing a wide torque range from 10 to 26 Nm and ratios from 1.35:1 to 14,340.31:1.

With its one-piece machined construction including integrated flange and bearing sets, the UNICASE housing design provides trouble-free operation and allows for a robust solution that can withstand extreme loads.

The bridge drives for the new crane were custom manufactured by German drive technology manufacturer NORD Drivesystems.

To solve the synchronisation issue, NORD recommended a motor-mounted frequency inverter for straightforward installation that makes shielded cables unnecessary. NORD has a comprehensive drive electronics program with graded performance and functional range options that allows users to choose suitable compact solutions with the exact features required for any given task, optimising budget and resource use.

The SK 205E inverter chosen for the project realises drive functions such as ramp-up: the inverter ensures the motor starts slowly with high torque, thereby protecting the mechanics from the extreme loads experienced when the heavy overhead crane starts from a standstill. An external brake resistor accommodates the regenerative current when the crane is decelerated.

The solution consisted of two flange-mounted NORDBLOC.1 geared brake motors, each fitted with an SK 205E frequency inverter and an external brake resistor.

The inverter is also equipped with an integral 24 VDC power supply to provide the internal control voltage, requiring only a power connection and no separate control cable.

“Throughout the process, NORD offered us abundant amounts of support from trained professionals and worked with us to achieve the best outcome,” said McDiarmid. “No problem is too big for NORD!”