Your material handling and manufacturing processes need to be exact and precise. When you use devices like indexers for welds, transfer cars for chassis delivery, and even a specialized conveyor system for an automatic picking/ distribution system, there is a power transmission system that will work together to create exacting, precise starts and stops to meet your process needs.
Intermittent motion projects require specialized products and engineering expertise to meet your application needs. The products used to deliver the motion and precise starts and stops need to work together. An important component of the power transmission system is the gearbox which translates the motor speed into torque so your material handling solution is optimized to meet your needs. In this post, we will talk about gearboxes for intermittent material handling projects requiring precise or frequent start and stop points.
Gearbox 101
In its simplest terms, the gearbox is the interface between the electric AC induction motor powering an application and the actual movement of the load. It translates the RPM of the motor into the appropriate linear speed to drive the load. If you were to open a gearbox, it would be a series of actual gears in a self-contained box where the number of teeth on the gears ultimately defines your gearbox ratio. The speed at the output of the gearbox is directly proportional to this gear ratio, meaning that if your 1750 RPM motor is attached to a gearbox with a 10:1 gear ratio, the output RPM at the gearbox will be 175 RPM.
The forces put on these gears inside the gearbox are torque, or rotational forces of motion. The gearbox increases torque, like in the example above with a gearbox with 10:1 gear ratio that increases the torque at the gearbox output shaft by a factor of 10. An everyday example of torque could be twisting a doorknob to enter a room or the rotation of the crankshaft as it rotates the connecting rods, and pistons in the engine of your car. Brake torque is also multiplied by the gear ratio so precise starting and stopping points can be achieved without installing larger motor brakes.
A gearbox is not the only way to create torque in an engine or motor setup. A great example is the chain, gears and pedals on your bicycle or the chain and sprocket on a dirt bike. Though these are both great ways to create torque, they can create safety issues and application issues in industrial applications. Since these are traditionally open to the environment, there is potential for damage from passing forklifts or safety issues for your workforce if they get caught up in the chain. In addition, if you need to have precise start and stop locations in your process, these types of gearing will not provide the precision you need for your application.
Torque and Horsepower
Horsepower and torque are proportionally related forces. In industrial applications, when you are using a gear motor and gearbox in your application, you would focus on horsepower. Horsepower describes the total motor performance of a drive system. In the world of automotive racing engines, we hear about horsepower much more commonly than torque because horsepower is a gauge of the power of the entire engine system rather than the maximum gauge of one component. When you are using a mechanical AC induction motor, torque is the more important aspect because the output torque of the gearbox is actually what moves the load and determines how reactive and precise the application can be.
If you decide to use a mechanical AC motor and gearbox, there are 2 types of torque to think about. Allowable input torque is the total torque the gearbox shaft can take coming in from the motor. This is important to assure the gearbox is sized properly to your application. Rated output torque is the torque generated by the motor multiplied by the gear ratio. This takes inefficiencies out to show the real torque rating. Rated output torque is critical because this is what actually moves the load through the output shaft of the gearbox. It is also important when you require intermittent motion and precise start and stop points because your application needs enough torque to move and stop the load properly. Torque is really what does the work in these applications.
Gearbox Efficiency and Why it Matters
One aspect to keep in mind for choosing a gearbox for your intermittent motion application is efficiency. Efficiency in a gearbox basically tells you how much torque is lost as the motor speed is slowed or increased by the gearbox. Efficiency is affected by how the gears physically work, or the design of how motion and torque is translated from the motor to the load. It can even be affected by the design of the oiling or lubrication within the gearbox. Efficiency can have effects on your applications, especially when precise starts and stops are necessary. You may never get 100% efficiency out of a gearbox but it’s finding what works for your goals in your application. At the end of the day, working with an expert to create the solution you need will assure your application will perform to your needs.
Choosing a Gearbox for Your Intermittent Motion Application
One type of gearbox that is not ideal for intermittent motion and precise start and stop applications is a Worm Gearbox. These gearboxes are an inexpensive option that works for only specific, simple applications. The problem with worm gears is how highly inefficient they are. Efficiency, 30-40%, is lost simply due to how the gears inside function. Worm gears cannot precisely start and stop so when your requirements include these and other factors, you should look for higher quality gearbox options.
Higher quality gearboxes allow the gears to deliver more precise motion and starting and stopping points due to the way the gears work within it. The ideal types for intermittent motion and precise start and stop points include Helical style gearboxes, Bevel style gearboxes and Hypoidal style gearboxes. These style gearboxes are very efficient, typically 90% or higher, making torque precise and exacting. These gearboxes come in configurations to meet your envelope needs, whether you need something that is inline, offset, or right angle. Because these style gearboxes are efficient, motor frame sizes could possibly be decreased because there is very little power loss through the gearbox which allows you to still meet the application needs.
What happens if I don’t choose the right one?
In order to have precise starts and stops for intermittent motion, matching the gearbox and AC motor is necessary. Unfortunately, choosing the correct combination isn’t so straight forward. The gearbox acts as the torque multiplier. The torque generated in the motor at the output shaft will increase torque proportionally to the gear ration of the gearbox, such as 10:1. This means the output from the gearbox shaft to the motor shaft is 10 times higher.
Lowering the speed of the entire system through a gearbox decreases the required torque at the load. Because of this, this also means you can potentially use a smaller, less powerful motor to move the same large load. To add more context to this without getting into an engineering lecture, here’s another way to look at it. If you are moving a very heavy load on a transfer car and you are travelling at a certain linear speed, you can calculate the torque required to effectively move the load. However, if you were now to cut that linear speed in half and your capacities remained the same, you would only require half of the original motor torque. This could mean you would be able to use a much smaller motor to get the job done.
An incorrectly sized product or choosing the wrong style product can lead to product failure, incorrectly fitting the envelope, or even not meeting your precise positioning needs. There are a few things you can do to make sure you’re covering all your bases. Don’t be afraid to research similar applications out there. This can give you an idea of what you’re looking for and what the solution looks like that may meet your needs. Working with an expert with experience designing systems like the application you’re looking for can help assure the final design will meet your needs.
Gearboxes are just one component of a drive system of an indexer or coil car. The gearbox is important because it creates the torque necessary for precise movement and stops. Choosing a higher quality gearbox, like a helical style gearbox, can deliver high efficiency and high precision to your application. When you are designing a material handling system requiring precise starting and stopping points with intermittent motion, it’s best to partner with the experts. As you research the needs for your application, look for similar applications and talk to engineers to learn about the possibilities.
Learn the basics of choosing an AC induction motor for your intermittent motion project. We take you through considerations as look at electromechanical motor options.
Understand the wheel, wheel block, and wheel system options available as you’re planning your project. Read more in our Wheels 101 post: Industrial Wheels 101- Understanding the Options to Move Heavy Loads Across Your Factory.