Tech Tip - AC Motors Advantages and Disadvantages
The most customary and basic industrial motor is the 3-phase AC induction motor, sometimes shortened to AC Motor. Pertinent detailed information can be found about AC motors by checking the nameplate.

Advantages of Using AC Motors

• AC Motors are of a basic design
         • The basic design AC motors: Simply stated, a series of 3 windings in the exterior stator section with a basic rotating section (rotor). The changing field caused by the 50 or 60 Hertz AC line voltage causes the AC motor rotor to rotate around the axis of the motor.
         • The speed of AC motors will depend upon these 3 variables:
                   1. The fixed number of winding sets (poles) built into AC motors, which determines the motor's base speed.
                    2. The frequency of the AC line voltage. Variable speed drives change this frequency to change the speed of AC motors.
                    3. The amount of torque loading on AC motors, causes slipping.
• AC Motors are of a low cost construction
AC motors have the advantage of being the lowest cost motor. AC motors are perfect for applications requiring more than about 1/2 hp (325 watts) of power. This is due to the basic design of AC motors. For this reason, AC motors are commonly chosen for fixed-speed applications, such as in industrial applications and for commercial and domestic applications where AC line power can be easily attached. Over 90% of all motors are AC induction motors. They are found in air conditioners, washers, dryers, industrial machinery, fans, blowers, vacuum cleaners, and several other applications.

• AC Motors operate reliably
The basic design and construction of AC motors casue them to be intensely certain and are thought to be low maintenance. Unlike DC Brush Motors, there are no brushes to replace. If AC Motors are used in the applicable environment, protected by an enclosure, AC motors can expect to replace the bearings after several years of continuous operation. If the application is well designed in a guarding environment, AC motors may not require the bearings to be replaced for more than 10 years.

• Easily Found Replacements
The extensive use of AC motors in several contrasting industries has resulted in easily found replacements for existing equipment repairs and/or upgrades. Several manufacturers adhere to either European (metric) or American (NEMA) standards.
• AC Motors are made by several manufacturers , so it is relatively easy to obtain replacements (for basically the same motor)
• AC Motors are designed in a variety of mounting styles (dependent upon the motor manufacturer). Foot Mount, C-Face, Large Flange, Vertical and Specialty.
• There are several environmental styles available for AC Motors, to include a all-inclusive range of applications and industries, called Specialty AC Motors by most. Because of the all-inclusive range of environments in which people want to use AC motors, manufacturers have adapted by providing a all-inclusive range of packaging/enclosure designs, such as Open Drip Proof (ODP), Completely Enclosed/Fan-Cooled (TEFC), Completely Enclosed/Air-Over (TEAO), Completely Enclosed/Blower-Cooled (TEBC), Completely Enclosed/Non-Ventilated (TENV), and Completely Enclosed/Water-Cooled (TEWC) versions.

Disadvantages of Using AC Motors

• High-priced speed control - Speed controllers can be high-priced. The electronics required to handle an AC inverter driver are considerably more high-priced than those required to handle a DC motor. However, if performance requirements can be met ~meaning that the required speed range is over 1/3rd of base speed ~ AC inverters and AC motors are usually more cost-effective overall, than are DC motors and DC drives. This is especially valid for applications larger than 10 horsepower, because of cost savings in the AC motor.
• Inability to operate at low speeds - Standard AC motors should not be operated at speeds less than about 1/3rd of the base speed, due to thermal considerations. A DC motor should be thought to be for these applications.
• Exhaused positioning control - Positioning drivers and controllers can be high-priced and crude. Even a vector drive is exceptionally crude when controlling a standard AC motor. Stepper motors and Servo Motors are more applicable for applications wherein positioning and speed control is crucial.

HMI Convenience
The convenience that comes with an HMI is invaluable; you will find that once you have digitized your system the functionality you will get out of your HMI is utterly unbeatable. A HMI combines all the control features that are found throughout your automation line and places them all in one center location; no more having to run to the red pushbutton that will stop your line. With remote access you won't even have to be anywhere near your automation line to start/stop or monitor production. With remote access you can have all the same features you have on your centralized unit in a more compacted form. Along with ease of access from wherever you may be, simplicity is also a large factor in the usability of a HMI. With simplistic screens and functions you can train nearly anyone to supervise your automation line.

Flexible Couplings Balance
Flexible couplings are usually balanced at the factory before they are shipped, but every once in a while they go out balance during operation. Re-balancing flexible couplings can be costly and difficult; it is usually only done when operating tolerance effort outweighs the cost. The characteristics of the particular connected machines dictate the amount of flexible couplings unbalance that can be tolerated by any system; this can be determined by experience or detailed analysis.

How to Select Stepper Drivers
The amount, speed, and direction of rotation of a standard stepper motor are determined by the applicable configurations of digital control devices. Selecting the most compatible stepper drivers, motors, and/or controllers, can save the user money and be a less burdensome motion control solution. We categorize the main types of digital control devices as follows:

• Stepper Drivers – offered in full-step, half-step and micro-step
•Standard Stepper Motor Controllers (sometimes referred to as Control Links – controllers indexers, and pulse generators sold separately or in drivers packs
• Standrard Stepper Motor Driver Packs – packaged units that include drivers and optional controller, with a matched power supply (some models are enclosed units that are fan-cooled)
• Integrated Stepper Drivers/Controllers – packaged at the end of a standard stepper motor are drivers and simple controllers (only available for high-torque stepper motors)

Stepper drivers provide a method to accurately control speed and positioning. With each pulse converted into digital data, the motor is able to undergo an exact incremental rotation without the need for feedback mechanisms i.e. tachometers or encoders. With an open-loop system, the problems of feedback loop phase shift and resultant instability, common with servo drives, are eliminated. Before a designer selects an apporpirate stepper drivers and motor combination for an application, there are certain variables needed to be considered. A designer must examine various parameters such as load characteristics, performance requirements, and mechanical design including coupling techniques for an optimal solution for a stepper drivers and motor combination. Failure to do so can result in poor system performance or cost more than necessary. For optimum stepper drivers motion control, the following factors should be taken into consideration:

1. Parameters:
   a. Distance to be traversed
 &nbps; b. Maximum time allowed for a traverse
  &nsbp;c. Desired detent (static) accuracy
   d. Desired dynamic accuracy (overshoot)
   e. Time allowed for dynamic accuracy to return to static accuracy specification (settling time)
   f. Required step resolution (combination of step size, gearing, and mechanical design)
   g. System friction: All mechanical systems exhibit some frictional force. When sizing the motor, remember that the most must provide enough torque to overcome any system friction. A small amount of friction is desired since it can reduce settling time and improve performance overall
   h. System inertia: An object’s inertia is a measure of its resistance to changes in velocity. The larger the inertial load, the longer it takes a motor to decelerate or accelerate the load. The speed at which the motor rotates is independent of inertia. For rotary motion, inertia is proportional to the mass of the object being moved times the square of its distance from the axis of rotation
   i. Speed/Torque characteristics of the motor: Torque is the rotational (in ounce-inches) defined as a linear force (ounces) multiplied by a radius (inches). When selecting a stepper drivers and motor, the capacity of the motor should exceed the overall requirements of the load. The torque any motor can provide varies with its speed.
Individual speed/torque curves should be consulted by the designed for each application    j. Torque-to-Inertia Ratio: This value is defined as a motor’s rated torque divided by the rotor’s inertia. This ration (measurement) determines how quickly a motor can accelerate and decelerate its own mass. Motors with comparable torque ratings can have different torque-to-inertia ratios as a result of varying construction
   k. Torque margin: Whenever possible, stepper drivers which can provide more torque than is needed should be specified. This torque margin allows for mechanical wear, lubricant hardening, and other unexpected friction. Resonance effects can cause the motor’s torque to be slightly lower at some speeds. Selecting stepper drivers and motors system that provides at least 50% margin above the minimum required torque is ideal. More than 100% can prove too costly

2. Calculation: Measurement of inertia, friction and workloads reflected to motor.
   a. In an open-loop stepper drivers system, the motor does not “know” if excessive inertia or friction has made the motor lose or gain one or more steps, thus affecting the position accuracy
   b. Load inertia should be restricted to no more than four times motor rotor inertia for high performance (relatively quick) systems. A low performance system can deliver step accuracy with very high inertia loads, sometimes up to ten times rotor inertia. System friction may enhance performance with high inertia loads

Experimentation: Tailoring
Experimentation for motor sizing is crucial due to dynamic changes in system friction and inertia, (load anomalies) which are difficult to calculate. Motor resonance effects can also change when the motor is couple to its load

How to Select Appropriate Spur Gearboxes
When considering spur gearboxes, several factors need to be addressed to meet specific application requirements:

Gear Ratio
Gear ratios are defined as the relationship between the numbers of teeth of two different gears. Commonly, the number of teeth a gear has is proportionate to its circumference. This means that the gear with a ampler circumference will have more gear teeth; therefore the relationship between the circumferences of the two gears can also give an accurate gear ratio. For example, if one gear has 36 teeth while another gear has 12 teeth, the gear ratio would be 3:1.

Output Torque
Output torque of spur gearboxes is reliant on the gear ratio used. To obtain a high output torque, an ample gear ratio would be selected. Using an ample gear ratio will lower the output shaft speed of the motor. Inversely, using a lower gear ratio, a smaller output torque value would be delivered into the system, with a greater motor speed at the output shaft of the spur gearboxes. This statement illustrates the relationship that both speed and torque are inversely proportionate to one another.

Speed (RPM)

Speed is proportionate to the gear ratio of spur gearboxes. For example, if the input gear has more teeth than the output gear, the result will be an boost in speed at the output shaft. On the other hand, having the reverse scenario with more gear teeth at the output compared to the input will result in a decrease of speed at the output shaft. In general, the output speed can be determined by dividing the input speed by the gear ratio. The higher the ratio the lower the output speed will be and vice versa.

Gear Arrangement
Gear arrangement is an ingenious engineering design that offers several benefits over the traditional stationary axis gear system design. The unique combination of both power transmission efficiency and compact size allows for a lower loss in efficiency of spur gearboxes. The more effective the gear arrangement, (i.e. spur, helical, planetary and worm) the more energy it will allow to be transmitted and converted into torque, rather than energy lost in heat.

Another application factor to be taken into account when selecting spur gearboxes is load allocation. Since the load being transmitted is shared among several planets, the torque capacity is increased. The higher number of planets in a gear system will amplify the load ability and enhance torque density. Gear arrangements improve balance and rotational stiffness because of a balanced system, but it is a complex and more costly design.

One example is a gear arrangement that is a traditional stationary axis gear system with a pinion driving a ampler gear on an axis parallel to the shaft. Or, there may be a planetary gear design system with a sun gear (pinion) surrounded by more than one gear (planet gears) and is encompassed in an outer ring gear. The two systems are like in ratio and volume, but the planetary gear design has three times the higher torque density and three times the stiffness due to the increased number of gear contacts.
Fixed Axis Gear System:
   Volume = 1, Torque = 1, Stiffness = 1
Planetary Gear System:
   Volume =1, Torque = 3, Stiffness = 3
Other gear arrangements as mentioned in the "Types of Spur Gearboxes" segment of this guide are bevel, helical, cycloid, spur and worm.

Backlash
Backlash is the angle in which the output shaft of spur gearboxes can rotate without the input shaft moving, or the gap between the teeth of two adjacent gears. It is not needed to consider backlash for applications which do not involve load reversals. However, in accurate applications with load reversals like robotics, automation, CNC machines, etc., backlash is crucial for precision and positioning.

How to Select Appropriate Planetary Gearboxes
When looking at planetary gearboxes, quite a few factors need to be considered to meet specific application requirements:

Gear Ratio
Gear ratios are correlation between the numbers of teeth of two different gears. Generally, the number of teeth a gear has is proportionate to its circumference. This means that the gear with a larger circumference will have more gear teeth; so the relationship between the circumferences of the two gears can also give an precise gear ratio. For instance, if one gear has 36 teeth while another gear has 12 teeth, the gear ratio would be 3:1.

Output Torque
Output torque of planetary gearboxes depends on the gear ratio used. To obtain a high output torque, one would select a larger gear ratio. Using a large gear ratio lowers the output shaft speed of the motor. Inversely, using a lower gear ratio means that a smaller output torque value would be delivered into the system with a greater motor speed at the output shaft of the planetary gearboxes. This illustrates the relationship that both torque and speed are inversely proportionate to each other.

Speed (RPM)
Speed is proportionate to the gear ratio of planetary gearboxes. For instance, if the input gear has more teeth than the output gear, the result will be an increase in speed at the output shaft. However, having the reverse scenario with more gear teeth at the output compared to the input will result in a decrease of speed at the output shaft. Overall, the output speed can be determined by dividing the input speed by the gear ratio. The greater the ratio, the lower the output speed will be and vice versa.

Gear Arrangement
Gear arrangement is an exceptional engineering design that provides assorted benefits over the traditional fixed axis gear system design. The combination of both power transmission efficiency and condensed size allows for a lower loss in efficiency of planetary gearboxes. The greater the efficiency of the gear arrangement, (i.e. spur, helical, planetary and worm) the more energy it will allow to be transmitted and converted into torque, instead of energy lost in heat.

Another factor to be taken into account when selecting planetary gearboxes is the load distribution. Since the load that is being transmitted is shared by multiple planets, the torque capacity is increased. The greater number of planets in a gear system will increase the load ability and enhance torque density. Gear arrangements increase stability and rotational stiffness because of a balanced system, though it is a complex and more costly design.

One example is a gear arrangement which is a traditional fixed axis gear system with a pinion driving a larger gear on an axis parallel to the shaft. There may also be a planetary gear design system with a sun gear (pinion) surrounded by more than one gear (planet gears) and is encompassed in an outer ring gear. The two systems are akin to each other in ratio and volume, but the planetary gear design has three times the higher torque density and three times the stiffness because of the increased number of gear contacts. Fixed Axis Gear System:
   Volume = 1, Torque = 1, Stiffness = 1
Planetary Gear System:
   Volume =1, Torque = 3, Stiffness = 3
Other arrangements, mentioned in the "Types of Planetary Gearboxes" segment of this guide, are bevel, helical, cycloid, spur and worm.

Backlash
Backlash means the angle in which the output shaft of planetary gearboxes can rotate without the input shaft moving, or the gap between the teeth of two adjacent gears. It is unnecessary to consider backlash for applications that do not involve load reversals. Though, in precision applications with load reversals like robotics, automation, CNC machines, etc., backlash is absolutely crucial for precision and positioning.

Advantages and Disadvantages
The most ordinary and basic industrial motor is the 3-phase AC induction motor, often shortened to AC Motor. Detailed information can be found about AC gearmotors by checking the nameplate.

Advantages of Using AC Gearmotors

• AC Gearmotors are of a standard design
    • The standard design AC gearmotors: Basically, a series of 3 windings in the exterior stator section with a basic rotating section (rotor). The changing field, caused by the 50 or 60 Hertz AC line voltage, in turn causes the AC motor rotor to rotate around the axis of the motor.

• The speed of AC gearmotors is reliant upon these variables:
    1. The fixed number of winding sets (poles) integrated into AC gearmotors, which decides the motor's base speed.
   2. The frequency of the AC line voltage. Variable speed drives alter this frequency to change the speed of AC gearmotors.
   3. The amount of torque loading on AC gearmotors, causes slipping.
• AC Gearmotors are of a inexpensive construction

AC gearmotors are advantageous in that they are the least expensive motor. AC gearmotors are excellent for applications requiring over about 1/2 hp (325 watts) of power. This is due to the fundamental design of AC gearmotors. Due to this, AC gearmotors are commonly preferred for fixed-speed applications, such as in industrial applications and for commercial and domestic applications where AC line power can be easily attached. More than 90% of all gearmotors are AC induction gearmotors. They can be found in air conditioners, washers, dryers, industrial machinery, fans, blowers, vacuum cleaners, and many other applications.

• AC Gearmotors operate dependably

The highly basic design and construction of AC gearmotors casue them to be extremely reliable and are considered to be low maintenance. Whereas DC Brush Gearmotors require brush replacements, AC motors have no brushes to replace. If AC Gearmotors are employed in the apropos environment, protected by an enclosure, AC gearmotors can expect to replace the bearings after several years of continuous operation. If the application is well designed in a protective environment, AC gearmotors may not require replacement bearings for more than 10 years.

• Easy To Find Replacements

The broad use of AC gearmotors in multiple industries has resulted in easily found replacements for existing equipment repairs and/or upgrades. Numerous manufacturers adhere to either European (metric) or American (NEMA) standards.

• AC Gearmotors are made by quite a lot of manufacturers , so it is relatively easy to obtain replacements (for basically the same motor)
• AC Gearmotors are made in a variety of mounting styles (reliant upon the motor manufacturer). Foot Mount, C-Face, Large Flange, Vertical and Specialty.
• There are various environmental styles available for AC Gearmotors, to cover a wide array of applications and industries, called Specialty AC Gearmotors by most. Due to the wide range of environments in which people want to use AC gearmotors, manufacturers have adapted by providing a wide array of packaging/enclosure designs, such as Open Drip Proof (ODP), Totally Enclosed/Fan-Cooled (TEFC), Totally Enclosed/Air-Over (TEAO), Totally Enclosed/Blower-Cooled (TEBC), Totally Enclosed/Non-Ventilated (TENV), and Totally Enclosed/Water-Cooled (TEWC) versions.

Disadvantages of Using AC Gearmotors

• Expensive speed control - Speed controllers can be costly. The electronics necessary to handle an AC inverter driver are considerably more pricey than those required to handle a DC motor. However, if performance constraints can be met (meaning that the required speed range is over 1/3rd of base speed ) AC inverters and AC gearmotors are nearly always more cost-effective overall, than are DC gearmotors and DC drives. This is especially true for applications greater than 10 horsepower, because of cost savings in the AC motor.
• Inability to be operated at low speeds - Standard AC gearmotors shouldn't be operated at speeds of less than about 1/3rd of the base speed, due to thermal considerations. A DC motor should be taken into account for these applications.
• Poor positioning control - Positioning drivers and controllers can be costly and clumsy. Even a vector drive is very crude when controlling a standard AC motor. Stepper gearmotors and Servo Gearmotors are more apropos for applications wherein positioning and speed control is critical.