5 tips prior to designing the gear motors

Saturday - 22/06/2019 22:15

5 tips prior to designing the gear motors

We could say gear motors are considered to be a fundamental part in industry. Their applications are endless, and they have always been the central part of the most precise motions and displacements in machines.
Thanks to treatments and breakthroughs in the materials used for their construction, in conjunction with new generations of electric motors such as step motors or servomotors, gear motors have never been as precise and reliable as they are today.

Do you need to use a gear motor on a company project? Below we bring you 5 tips you should have in mind before designing a gear motor that meets all your expectations.

     Power and speed reduction: gear motor calculation

These are the parameters that will dictate the gear motor’s behaviour. We will have to determine the output and input shaft speeds for the mechanism.  

In this regard, one of the main issues emerges when attempting to determine the range of speeds that offer the machine a versatile motion. Here, a speed reducer for a fixed output shaft speed of X rpm is calculated, and this is then used as a basis for developing the design of the rest of the mechanism.

Once the speed reducer behaviour is clear to us, we should calculate the required power. To this end, we can consult with electric motor suppliers.  

    Gear motor efficiency

Broadly speaking, transmission mechanical components take advantage of part of the input energy and turn it into heat. When this happens, the operational speed is increased until it reaches a balance between the energy being absorbed and the heat being dissipated towards the atmosphere through some cooling system.

When this balance is reached, the mechanical power at the input shaft equals the mechanical power at the output shaft, plus the energy dissipated as heat.
Dolin three phase motor

In other words, the output power available for a gear motor equals the input power minus the unavoidable loss due to heat. The concept of efficiency tells us how much energy is lost, which we should keep in mind in order to know the energy expenditure necessary in certain life cycles. To sum up, efficiency tells us that the output power available for each element will equal the input power multiplied by its efficiency.

Lastly, we should keep in mind that the efficiency for gears working at low speeds are usually inadequate, they provide less torque for start-up and acceleration.

     The amount of start-ups and the service factor

As you probably know, not all machines work at a constant speed and with a constant load. The most common is for stops and start-ups to take place with some frequency, and for the operation speed to fluctuate.

At each start-up, the motor and the transmission have to accelerate the machine from a complete rest up to the optimal operational speed. This fact implies that, for a specific period, the torque transferred will be higher than that of stable operation.

The torque transferred can also increase when there are fluctuations in the load or the speed. Traditionally, these variations are controlled through the application of the service factor, which are multiplied by the optimal operation torque in order to define the selection torque (also called the design torque).

At this point, motor and gear motor manufacturers publish charts where they include the service factors, as well as the following information: type of motor, quantity of start-ups per hour, the amount of operation hours per day, and the torque variations depending on the type of operation for the machine.

The service factor usually has a value of 1.0 for machines driven by electric motors, for continuous operation (8 hours a day), under 10 start-ups per hour and no important variations in regards to the speed or load.

    Noise and load

Noise will probably be a significant aspect when operating your future gear motor. You can never go wrong with helical gears. They tend to be more silent than spur gears since they operate with a better slip.

Another important aspect will be vibrations and resistance to shock loading inside the gearbox. Speed reducers with helical gears are once again the best choice. They have a greater resistance to shock loading than spur gears do.

    Gear motors service life

It can be affected by many factors, the most important ones being speed, load, duty cycle or environmental conditions (humidity, temperature, salinity, etc.).

Selection of gear motor components, as well as the surface treatments their parts may be subjected to, will greatly affect the precision and service life of the actuation mechanism.

Other details that may affect a gear motor here are the types of rolling bearings of the motor’s shaft. In addition to affecting its efficiency, they may affect their operation and durability.

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