Traveling inverter control methods have replaced traditional 2-speed contactor controls for the trolley and bridge motions on overhead bridge cranes. In the overhead bridge crane industry, 2-speed contactor control methods for traveling motions have become an outdated form of technology.
Why are inverter-controlled traveling motions replacing traditional two-speed contactor control?
Inverter controls provide many advantages versus a traditional 2-speed contactor control in the form of safer working environments, flexibility, increase in throughput, and increase in longevity of the equipment.
Inverter drives offer built-in flexibility such as speed control types (stepless, multi-step), selection of output speeds as well as providing over current protection, and smoother starts and stops. Allowing an operator to dictate and control the speed at which the load is moving provides an operator with the flexibility to safely control the load of which they are moving.
What additional flexibility does an inverter drive provide versus traditional 2-speed contactor controls?
2-speed contactor controls allow the operator restricted speeds of high and low. Generally, these speeds are somewhere in the ball park of a 4:1 ratio and have no diversity. Inverter drives allow for multiple speed programming types. Infinitely variable is the more commonly used type of speed control. Infinitely variable speed control is stepless, meaning it gives the user flexibility to control, accelerate and hold any speed from the minimum speed up to the maximum speed. Multi-step speed control gives the user two, three, four, or five distinct and programmable operating speeds depending on the inverter capabilities.
An inverter drive allows for a smooth start and stop which results minimal “load swing” during operation. The minimizing of “load swing” provides an advantage in the fact that the operator can better manipulate the load, allowing for faster operation and increased throughput / productivity.
How does an inverter drive’s dynamic braking function increase longevity and lifespan of the equipment?
Dynamic braking is where the inverter does the braking when the operator releases the control device (i.e. pushbutton), and as the output frequency decreases to near zero, then the brake interlock relay sets the motor brake. This function helps minimize wearing of the motor brake allowing for an increased lifespan of not just the motor and brake but other items that are impacted by a sudden brake actuation. Think of all the items on a car that would be impacted if driving down the highway and immediately slamming on the brakes. On a smaller scale, dynamic braking helps minimize these same consequences.
Inching control provides a way to approach the load destination with great accuracy in small increments of movement - essentially moving the load inches at a time.
Micro-speed control feature provides a way to approach the load destination with great accuracy through a slow speed range. The maximum micro speed is scaled with a desired value range of 1%-99%, depending on the requirements of the application.
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