Belt conveyors form the heart of modern-day material handling systems. Drum motors, which are compact drives for belt conveyors, are available in asynchronous and synchronous models. But how do these two technologies differ and what are their benefits?
The quantity of goods being conveyed in industrial environments is getting ever larger, while goods themselves are becoming more complex and more customized all the time. Although electric motors are traditionally used to drive belt conveyors, a trend towards drum motors is emerging. In contrast to classic gear motors, which usually have to be fitted underneath or next to the conveying line and be driven by a power transmission system or several conveyor rollers, the drive for drum motors is built into the roller, thus eliminating the need for an external power transmission mechanism.
This makes drum motors perfect for building extremely compact and energy-efficient conveying solutions. They are also very easy and cost-effective to fit, and comparatively easy to service and repair. Furthermore, this type of motor has a hermetically sealed design, which is advantageous in environments where hygiene is of utmost importance and areas requiring thorough, regular cleaning.
Asynchronous or synchronous drum motors: The choice is yours
Brushless motors are preferred for this as they naturally suffer very little wear and they have low susceptibility to faults. Here, a basic distinction must be made between synchronous and asynchronous motors.
In industrial applications today, asynchronous motors are by far the most commonly used type of motor. They are robust and comparatively cheap to manufacture. They are highly efficient and can be operated at constant transport speeds without the need for an additional electronic control system. Asynchronous motors are, therefore, usually the first choice for applications involving a steady flow of medium to heavy goods in standard speed ranges. They can normally be used to achieve material transport speeds of around 0.1 to 1 meter per second.
Synchronous motors satisfy a considerably wider range of applications
When using synchronous drum motors, the range of possible transport speeds is significantly larger, ranging from around 0.01 to just under 3 meters per second. For this reason, these drives are also suited to very slow-flowing processes, during which goods have to be machined manually, for example. Steady flow processes at high speeds—such as those required in distribution centers, for luggage belts or in automated packaging systems—can be implemented, too.
Synchronous drum motors make start/stop applications and exact positioning in the material flow possible
Only synchronous drum motors enable very quick and frequent stopping and starting, something that always makes them the best choice for handling intermittent flows of material, such as in automated filling or machining processes. Synchronous motors equipped with the right sensor technology also boast very precise speed and positioning behavior, which is required in automated cutting processes. Furthermore, they generate substantially higher torque than asynchronous motors in every speed range, making them capable of transporting heavier goods.
Due to their design, asynchronous motors—particularly those with a lower motor power in—have a considerably lower level of efficiency than synchronous motors. This means that synchronous motors use less electricity and therefore cost less to run in a material handling system. But they offer other benefits, too: As a direct result, synchronous motors remain cooler than asynchronous motors, as less of the electrical energy they are supplied with is turned into heat. This makes them more suitable for applications such as food processing in which the temperature is critical.
Compact solution: Even switching to synchronous motors is worthwhile
A further advantage of synchronous motors is that they offer the same power but are smaller in size, due in large part to the significantly smaller permanent magnet rotor. This is exactly what is fitted in the Interroll Synchronous Drum Motor, which measures just 81.5 millimeters in diameter and has a maximum power of 700 watts, with a minimum installation length of 290 millimeters. The equivalent asynchronous motor has a rated power of 750 watts, an external diameter of 138 millimeters and minimum length of 350 millimeters. The smaller diameter of synchronous drum motors makes conveying systems equipped with them considerably better suited to conveying both smaller and larger goods.
Switching from asynchronous to synchronous technology has numerous advantages when designing new systems and modernizing existing material handling systems, too. Replacing asynchronous motors with comparable synchronous motors offers substantially higher efficiency and flexibility, enabling any future changes in material handling requirements to be accommodated.