Variable frequency drives, or VFDs, are a type of AC motor controller that drive an electric motor by
varying the frequency and voltage supplied to it. VFDs are also commonly known as variable speed
or adjustable speed drives, AC drives, micro-drives or inverters - depending on the industry or
In the material handling industry, variable frequency drive controls are often used in electric hoists
as well as in overhead cranes and lifting systems. Drives are designed around a microprocessor,
which allows for the creation of programmable functions for specific applications.
Greater Speed Adjustment: VFD controls let you choose from multiple speeds, allowing you to customize your hoist, trolley, and bridge controls to your application.
Improved Load Control: Positioning a load using a single-speed hoist may cause shock loading or load swings. A VFD allows for smooth operation by gradually slowing down a load. Variable frequency drives also allow for smooth acceleration to prevent load swings in the traverse motions.
Duty Cycles: CMAA Class A-F. A VFD is concisely matched with a braking resistor, depending on the duty cycle of the motion. A regenerative drive may also be used, which is not dependent on duty cycle.
Efficiency: A VFD will only consume the power that's needed, thus saving energy compared to contactors and soft-starters.
Increased Hoist Life: Some variable frequency drives provide thermal overload and overcurrent protection for the hoist motor, prolonging its life. VFDs also utilize a ramp-down-to-stop method of braking rather than using brake shoes to slow down. The brake is only used for parking and emergency situations, which prolongs brake life.
Regenerative Energy: Deceleration and lowering of a hoist creates regenerative energy produced by the motor. This energy can be transformed into heat using a braking resistor or conditioned and send back to the source, thus netting energy savings. An AC regenerative drive will redistribute that energy, which would otherwise be wasted when converted to heat with a braking resistor.
Digital Diagnostics: Aid in maintenance and troubleshooting on the machine or remotely.
In recent years, the use of radio remote controls has become increasingly more common as an
alternative to a corded pendant assembly in the material handling industry. Why? Radio controls
have been found to increase safety and productivity while reducing downtime. In-field operators
have also found them easier to use than corded pendant assemblies. And, as technology continues
to evolve, radio controls have become more cost effective than ever.
Benefits of radio remote controls include:1. Increased Safety - Radio controls allow the operator to control the crane from a nearby location,
rather than being tethered to the crane with a hard-wired pendant cord. This increased mobility
allows the operator to position themselves at key locations throughout the lift, giving them the
- Avoid pinch points and trip hazards while moving
- Find better vantage points to insure the load's path is clear of obstructions
- Check the load fro all angles to insure that rigging remains in place to prevent load shifts
2. Increased Productivity - As previously mentioned, radio controls can improve operator mobility.
Not only does this increase safety, it can also reduce cycle times. The operator is not tethered to
equipment with a pendant, so they are free to move throughout the facility to keep production running
3. Decreased Downtime - When using pendants in material handling applications, it is not uncommon
for pendants to be damaged and require repair. When pendant repairs are needed, they often result in
longer downtimes when they are the primary means of control with no backup. This leads to the
equipment being unusable until the needed repairs are completed. When using radio controls, if a
transmitter is damaged, a spare transmitter can be put into operation immediately, which greatly
reduces the amount of time the crane is inoperable. It is also easier to protect transmitters from damage
in the first place, as they can be easily stored in a secure location when not in use, unlike a pendant that
is continually exposed to the workplace environment.
4. Ideal for Unique Applications - Radio remote control systems are ideal for several unique applications
where wiring can be cumbersome and time consuming to install, such as pitch and catch systems, tandem
or multiple unit control, and festoonless crane systems.