Types of Encoders within the MPL and 1326 Servo Motor Series
Have you ever wondered how forming and metal cutting machines provide precise motion for lathes, bending for metal fabrication and milling or how a robotic vehicle mainly used in military applications with bomb detection systems is controlled, or how antenna positioning systems control the precision in elevation and azimuth? Well, a servo motor is at the heart of these precise position and motion control systems.
A servo motor is a compact electrical component, which rotates parts of a machine with great precision and high efficiency. Its output shaft can be moved to a particular position, velocity, and angle which is not possible with a regular motor. This is because the servo motor utilizes a regular motor which is coupled to a sensor for feedback. An encoder is used as the feedback sensor, providing position and speed feedback. It achieves this by observing the change of position, mechanical motion, rate, and signals to the controller. The encoder also receives control signals from the controller.
While there are few encoder options for servo motors, it is important you chose the best feedback option, especially when accuracy, repeatability, and resolution are essential for your servo motor application. This article outlines the different types of encoders that are available with the MPL and 1326 servo motor series.
Encoders within the MPL Servo Motor Series
MP-Series™ Low Inertia (MPL) Servo Motors are compact brushless motors characterized by high torque output with reduced motor size. They are designed and produced by Allen-Bradley, to meet the demands for high-performance motion control systems.
In today’s position and speed control systems, a motor’s functionality goes beyond torque, inertia, and speed. It should also provide reliability for the proper functioning of the integrated encoder. The MPL servo motor series provides a wide range of counts per revolution (CPR) starting with lower-end versions which deliver up to 26,000CPR. To higher-end applications that can deliver up to 2 million counts per revolution. Also, the Allen Bradley MPL-Series support absolute position feedback with 4096 turns. This means that regardless of the type of your control system, MPL-Series provides both precise control and high performance. This is possible through the use of the following encoders:
A) Single-Turn High Resolution Encoder
Single-turn encoders are high-resolution absolute rotary encoders that measure speed, pivot position, or linear motion with one rotation of the shaft. Since they are rated to only measure position per single revolution, any motor shaft rotation beyond a 360o spin takes the counter back to the starting point and begins counting forward again. For instance, the encoder would read a 361o turn as 1o. Hence, single-turn encoders must have a defined starting position. So that as the servo motor output shaft turns 360o, its position is determined per turn depending on the set stop position. This encoder only reports the shaft position within the 360o range; it does not record the number of cycles or revolutions. An example of a single-turn high-resolution encoder used with the MPL servo motor series is the 845G Encoder-Series produced by Allen Bradley.
The 845G Single-Turn series of encoders provides a wide range of power supply options varying from as low as 5+/-5%V DC, 8-24V DC, and up to 10-30V DC. They also offer different code output types such as binary and gray code. You can use these encoders with various pin connections such as radial 19 pin and axial 19, 17, and 12 pins. The 845G single-turn encoders are capable of counting up to 4095 positions on a single servo motor shaft within a single turn. After 4095 positions, the counter returns to zero. Specifically, this encoder provides high-resolution feedback for an absolute position within one turn. Similar Allen Bradley single-turn encoders can be used with the different MPL-Series servo motors. Note that, single-turn encoders are well-suited for applications that require measurements of less than 360° of rotation, such as measuring partial rotations of a servo motor shaft or determining the pivot point of an angle.
|Type of MPL Servo Motor||Description||Feedback Device|
|MPL-A1520U-EJ72AA||Voltage rating 230V, Rated speed 7000 RPM, Stack Length 20 = 50.8 mm (2.0 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Single -Turn High Resolution Encoder|
|MPL-A320P-SK72AA||Voltage rating 230V, Rated speed 5000 RPM, Stack Length 20 = 50.8 mm (2.0 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Single -Turn High Resolution Encoder|
|MPL-A4540F-SJ72AA||Voltage rating 230V, Rated speed 3000 RPM, Stack Length 40 = 101.6 mm (4.0 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Single -Turn High Resolution Encoder|
|MPL-B680D-SJ72AA||Voltage rating 460V, Rated speed 2000 RPM, Stack Length 80 = 203.2 mm (8.0 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Single -Turn High Resolution Encoder|
|MPL-B540K-SJ74AA||Voltage rating 460V, Rated speed 4000 RPM, Stack Length 40 = 101.6 mm (4.0 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Single -Turn High Resolution Encoder|
|MPL-B1510V-EJ72AA||Voltage rating 460V, Rated speed 8000 RPM, Stack Length 10 = 25.4 mm (1.0 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Single -Turn High Resolution Encoder|
B) Multi-turn High Resolution Encoder (Absolute Feedback)
A Multi-turn encoder also measures the absolute position of a servo motor shaft. However, these encoders measure the degree of rotation within 360o and also track the number of total revolutions for the encoder shaft; they achieve this by using a unique word for each shaft position and number of revolutions. Thus, they can count up to 4096 steps on a single shaft rotation and then a total of 4096 shaft revolutions. When the encoder reaches 4096 revolutions, the values will begin to repeat. This is not to be confused with the 4095 steps counted by a single-turn encoder in one turn.
Also, multi-turn encoders can be used with the latest controllers that are fitted with a “modulo positioning” feature, which enables storage of overflow turn data for both partial and full rotations after 4096 revolutions. This data can then be used to determine the correct shaft position beyond the 4096 revolutions limit.
Multi-turn encoders are highly suitable for use as servo motor feedback devices if the application involves offset-coordinated axes. As with single-turn encoders, the axial offsets could be lost in case the system is affected by power failure or when the system needs to be homed. One could argue that a battery backup can prevent this, but the system’s position will still change if it is moved mechanically when the power is off (such as when the operator moves the servo motor’s or the encoder’s shaft). Thus, a multi-turn encoder is very useful in such a case, as the offset position can be programmed into its controller.
For instance, if you are using a servo motor to control the processing of a large wafer in a semiconductor manufacturing system, it would be impossible to rehome such a system and return it to its prior position in the event of a power failure; meaning that the entire wafer will be scrapped. Hence, in such applications using a multi-turn encoder will allow the system’s position to be mechanically saved on the encoder when blackouts occur.
An example of a multi-Turn encoder by Allen Bradley is the Multi-Turn Feedback Absolute Encoder — 842A-31GA.
The 842A multi-turn encoder is characterized by an operating voltage of 10-32V DC. Its power requirements are 150mA at 5V (with no load). It consists of an M23 connector. Its electromechanical design does not need a battery. To reset its output to zero shaft position and zero turns, you would need to remove the slotted cover at the back and press the button inside. Also, you can reset this encoder by momentarily connecting pin 9 to DC+ Input. This type of encoder provides high-resolution feedback for an absolute position within 4096 turns.
The table below lists examples of MPL-Series servo motors that are integrated with Multi-Turn absolute encoders similar to the 842A-31GA encoder:
|Type of MPL Servo Motor||Description||Feedback Device|
|MPL-A1510V-VJ72AA||Voltage rating 230V, Rated speed 8000 RPM, Frame Size 15 = 63 mm (2.48 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Multi-Turn High Resolution Encoder (Absolute Feedback)|
|MPL-A430P-MJ74AA||Voltage rating 230V, Rated speed 5000 RPM, Frame Size 4 = 115 mm (4.53 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Multi-Turn High Resolution Encoder (Absolute Feedback)|
|MPL-B1510V-VJ72AA||Voltage rating 460V, Rated speed 8000 RPM, Frame Size 15 = 63 mm (2.48 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Multi-Turn High Resolution Encoder (Absolute Feedback)|
|MPL-B680F-MJ74AA||Voltage rating 460V, Rated speed 3000 RPM, Frame Size 6 = 215 mm (8.46 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||Multi-Turn High Resolution Encoder (Absolute Feedback)|
C) 2000 Line Incremental Encoder
Generally, an incremental encoder is a rotary encoder that generates an output signal whenever the encoder shaft is rotated by a certain angle. Thus, it converts the angular position or motion of a shaft into a digital or analog code to determine position or velocity. This encoder’s internal components are simpler and more economical, as it does not output an absolute position so only a few sensors are required. The number of pulses(signals) per turn determines the resolution of the encoder. Thus, the 2000 Line incremental encoder has a resolution of 2000 Lines per Revolution (LPR) or 2000 Pulses per Revolution (PPR). Each line on the encoder optical disc would represent a low output pulse as they have a one-to-one relation.
Incremental encoders are mainly used to determine velocity, besides position tracking. To track the position, this encoder counts the number of pulses in relation to the starting point. While it retrieves the velocity of the servo motor by dividing the total number of pulses by the measured time interval. A 2000 LPR incremental encoder can be used with servo motors that require motor speed and positioning feedback for industrial applications, in-line manufacturing, and robotics. This is because it provides excellent speed and position feedback. They are the widely used rotary encoders.
An example of a 2000 lines/revolution incremental is the Allen-Bradley 847H-DN2A-AG02000 encoder, illustrated in the image below. This encoder requires a power supply of 8-30 Volt DC. Its resolution is 2000PPR, has a solid shaft with a 2.5-inch diameter. Its output configuration is 4.5-5.5 Volt Line Driver, TTL. Some of the MPL-Series servo motors integrated with similar 2000 lines/revolution incremental encoder are listed in the table below:
|Type of MPL Servo Motor||Description||Feedback Device|
|MPL-A310P-HJ72AA||Voltage rating 230V, Rated speed 5000 RPM, Frame Size 3 = 100 mm (3.94 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||2000 Line Incremental Encoder|
|MPL-A430H-HJ72AA||Voltage rating 230V, Rated speed 3500 RPM, Frame Size 4 = 115 mm (4.53 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||2000 Line Incremental Encoder|
|MPL-B220T-HJ72AA||Voltage rating 460V, Rated speed 6000 RPM, Frame Size 2 = 75 mm (2.95 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||2000 Line Incremental Encoder|
|MPL-B430P-HJ72AA||Voltage rating 460V, Rated speed 5000 RPM, Frame Size 4 = 115 mm (4.53 in.), Right Angle, 180° Rotatable, SpeedTEC DIN Connector||2000 Line Incremental Encoder|
Encoders within the 1326 Servo Motor- Series
The 1326 motors are a series of high-performance, medium-sized, brushless AC synchronous servo motors manufactured by Allen-Bradley/Rockwell Automation. They are designed to provide high-level continuous output with smooth performance. They are available in numerous frame sizes. They support torques ranging between 2.7N/m to 50N/m. In addition, this series of standard servo motors can be used with Allen-Bradley Ultra, Kinetix 600, or 1394 Servo Controllers. They regulate and control the positions of various electrical appliances.
One unique feature of the 1326 Motors is that they are rugged in nature, so they can withstand high operating temperatures and harsh environmental conditions. Their operating temperatures range between 0oC to 60oC. Hence, the 1326-Series feedback devices are standardized to enable them to withstand high operating temperatures, as well as vibration and harsh shock. These feedback devices include:
A) Resolver-Based Feedback
A resolver is an electro-mechanical transducer, that uses electromagnetic technology to determine the motion and position of an object. Also, referred to as motor resolvers, they are analog devices that provide continuous output through one complete mechanical revolution. Hence, theoretically, the resolution of a speed resolver is infinite. Though unlike incremental encoders, motor resolvers can only output analog data, thus, they require specialized and standard electronics to connect with.
However, the simplicity of the resolver design, in that the transformer design is simple and doesn’t have any onboard electronics, makes it the most rugged feedback device compared to other encoders. It is therefore the best choice for 1326 -Series servo motor feedback, for applications that require reliable performance in high temperature, high shock and vibration, radiation-exposed, and other extreme environments.
For example, 1326AB- Series servo motors are available with a rugged, brushless resolver that provides accurate position feedback; and can withstand high operating temperatures, vibration, and harsh shock while eliminating the need for on-board electronics in the servo motor. The 1326AB resolver feedback generates A quad B encoder output, equivalent to 2048PPR.
B) Rugged, Single-Turn and Multi-Turn Absolute Encoders
Like the MPL-Series servo motors, 1326-Series high-resolution servo motors are also fitted with single-turn and multi-turn configurations which allow the use of high-resolution encoder feedback for servo motor applications requiring precise position tolerance.
The Single-turn encoder used with the 1326-Series is similar in description to the MPL-Series single-turn encoder described above, but in this case, it is used to provide precise machine positions of 2 million CPR (counts per revolution). Likewise, the 1326-Series multi-turn encoder has similar functionality as the MPL-Series multi-turn encoder. Though with the 1326-Series, the multi-turn encoder used provides 1 million CPR of feedback and accurate absolute shaft positioning within 4096 revolutions. This encoder also eliminates the need for a battery backup or machine re-homing in the event of a power loss, by providing accurate absolute positions of the machine over multiple revolutions.
Both encoder configurations have an onboard EEProm memory used to store configuration information for the motor. Also, to better suit them for their applications with the 1326 Servo Motors, these absolute encoders feature a metal code disk and a robust mechanical design providing a rugged bearing system. They are also designed to withstand vibration, excess shock, and a wide range of operating temperatures from very cold to extremely high oC.
At the center of most manufacturing applications, and other industrial processes like warehousing is motion control. With accurate and precise motion control, system designers and engineers can create efficient closed-loop systems to optimize machine performance across a wide range of industries. One common requirement for these closed-loop systems is MPL-Series and 1326-Series servo motors by Allen Bradley. However, whenever you read the product description of such servo motors you will notice features like accuracy, repeatability, and resolution are not mentioned. That is because the MPL and 1326 servo motors rely specifically on feedback devices like encoders for precise position and speed feedback. This article has highlighted the general types of encoders that are readily available with the MPL-Series and 1326-Series motors. Making your encoder selection for such servo motors much easier.
We hope that this overview of encoders within the MPL and 1326 Servo Motor Series has been helpful in understanding your selection options. For more information or to discuss which equipment might be best for your application, please visit our website here, or contact us at email@example.com or 1-800-730-0292.