Are you struggling with your old overhead crane system to keep it up and running? It may feel like all you do is rip out the transmission and replace worn parts and couplers. Or maybe you regularly take equipment offline to replace worn brakes on your crane.
If this sounds familiar, you’re not alone. If your crane breaks down due to wearing parts or requires frequent repairs, you can extend its life with smarter, more efficient drive control systems.
1. The role of the frequency converter in the crane control system
Variable frequency drives were introduced to the material handling industry in the late 1980s and early 1990s after the introduction of low-cost high-speed power transistors. Frequency converters are designed to increase the precision and control of single- and two-speed motors.
Initially, they were only specified on bridges and trolleys for high-speed D- and E-class cranes. Today, they are used to controlling every electric movement on a crane – including hoist, bridge, trolley, and even hook rotation in some applications.
As the name implies, frequency converters vary the frequency of an AC motor by creating a sine wave. By varying the voltage and frequency supplied to the motor, the drive “tricks” the AC motor into thinking it is at synchronous speed, even though it is not. This creates better, smoother motor control and allows for adjustable speed control and adjustable acceleration and deceleration ramps.
As the cost of these systems has decreased, they have grown in popularity and are today specified for all types of crane systems – from low duty packaging crane systems, all the way up to high capacity/high duty cycle process cranes.
2. Why should a frequency converter be added to the crane control system?
Initially, VFDs were only available on high-speed D- and E-class cranes. Today, they are used to controlling every electric movement on a crane – including cranes, bridges and trolleys in almost any type of application.
Initially, VFDs were only available on high-speed D- and E-class cranes. Today, they are used to controlling every electric movement on a crane – including cranes, bridges and trolleys in almost any type of application.
Before the introduction of frequency converters, overhead crane operators used contactor-based controls to control their cranes. For low duty cycle cranes, the system is available with single or two speed motors. For cranes with higher duty cycles, they use so-called wound rotor motors.
Single or two speed motor
On single-speed motors, the operator presses a button and the motor accelerates as quickly as possible depending on the load. Once the button is released, the brakes engage and the crane stops. So if your crane is equipped with a motor that runs at 50 feet per minute (feet per minute), that’s the only speed it can work at.
On a two-speed motor, there are two speeds at which the crane can operate – usually within a 3:1 ratio. So if a crane is equipped with a two-speed motor, it can run at 40 fpm or 120 fpm, but no other speed options in between.
These low duty cycle applications can be equipped with “soft start” technology, also known as a reduced voltage starter. The technology reduces the voltage to the motor, which reduces acceleration at start-up and reduces the torque applied to the overhead traveling crane driveline during acceleration. However, this method of control generates a lot of heat and is not recommended for high use/high duty cycle cranes as it may overheat the motor quickly.
Wound Rotor Motor Control and DC Control
Many years ago, craft cranes and other high performance crane systems used an effective but rather complex motor control system known as wound rotor control. This consists of windings on the rotor of the motor, which is then brought to the slip ring, which leads to the brushes, and then to the resistor bank. Using this system, you can control the acceleration of the motor by changing the resistance on the motor’s rotor.
These systems work well, but troubleshooting is difficult due to all the wiring and complexity built into the system. Other high duty cycle cranes use high performance speed or DC controls to give the operator more control of the crane motor. These are still popular in factories today, but they are also an inefficient use of complex designs and controls.
Are you struggling with your old overhead crane system to keep it up and running? It may feel like all you do is rip out the transmission and replace worn parts and couplers. Or maybe you regularly take equipment offline to replace worn brakes on your crane.
If this sounds familiar, you’re not alone. If your crane breaks down due to wearing parts or requires frequent repairs, you can extend its life with smarter, more efficient drive control systems.
1. The role of the frequency converter in the crane control system
Variable frequency drives were introduced to the material handling industry in the late 1980s and early 1990s after the introduction of low-cost high-speed power transistors. Frequency converters are designed to increase the precision and control of single- and two-speed motors.
Initially, they were only specified on bridges and trolleys for high-speed D- and E-class cranes. Today, they are used to controlling every electric movement on a crane – including hoist, bridge, trolley, and even hook rotation in some applications.
As the name implies, frequency converters vary the frequency of an AC motor by creating a sine wave. By varying the voltage and frequency supplied to the motor, the drive “tricks” the AC motor into thinking it is at synchronous speed, even though it is not. This creates better, smoother motor control and allows for adjustable speed control and adjustable acceleration and deceleration ramps.
As the cost of these systems has decreased, they have grown in popularity and are today specified for all types of crane systems – from low duty packaging crane systems, all the way up to high capacity/high duty cycle process cranes.
2. Why should a frequency converter be added to the crane control system?
Initially, VFDs were only available on high-speed D- and E-class cranes. Today, they are used to controlling every electric movement on a crane – including cranes, bridges and trolleys in almost any type of application.
Initially, VFDs were only available on high-speed D- and E-class cranes. Today, they are used to controlling every electric movement on a crane – including cranes, bridges and trolleys in almost any type of application.
Before the introduction of frequency converters, overhead crane operators used contactor-based controls to control their cranes. For low duty cycle cranes, the system is available with single or two speed motors. For cranes with higher duty cycles, they use so-called wound rotor motors.
Single or two speed motor
On single-speed motors, the operator presses a button and the motor accelerates as quickly as possible depending on the load. Once the button is released, the brakes engage and the crane stops. So if your crane is equipped with a motor that runs at 50 feet per minute (feet per minute), that’s the only speed it can work at.
On a two-speed motor, there are two speeds at which the crane can operate – usually within a 3:1 ratio. So if a crane is equipped with a two-speed motor, it can run at 40 fpm or 120 fpm, but no other speed options in between.
These low duty cycle applications can be equipped with “soft start” technology, also known as a reduced voltage starter. The technology reduces the voltage to the motor, which reduces acceleration at start-up and reduces the torque applied to the overhead traveling crane driveline during acceleration. However, this method of control generates a lot of heat and is not recommended for high use/high duty cycle cranes as it may overheat the motor quickly.
Wound Rotor Motor Control and DC Control
Many years ago, craft cranes and other high performance crane systems used an effective but rather complex motor control system known as wound rotor control. This consists of windings on the rotor of the motor, which is then brought to the slip ring, which leads to the brushes, and then to the resistor bank. Using this system, you can control the acceleration of the motor by changing the resistance on the motor’s rotor.
These systems work well, but troubleshooting is difficult due to all the wiring and complexity built into the system. Other high duty cycle cranes use high performance speed or DC controls to give the operator more control of the crane motor. These are still popular in factories today, but they are also an inefficient use of complex designs and controls.
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