1326 Servo Motors
For motion applications that need precision, servo motors are the electronic devices in trend. These motors are for factory use only. 1326 servo motors by Allen Bradley are a family of high-performance motors which encompass all the needed features of high-quality servo motors. 1326 servo motors, coupled with an appropriate controller, are used for multiple applications. Majorly, these servo motors are used with 1391 controllers which are AC servo controllers in essence. These motors are AC motors, their construction is brushless, and their production of flux is synchronous. These motors are equipped with a resolver which gives sinusoidal or co-sinusoidal feedback for determining the position or speed of the rotor. The construction and specifications of these motors are discussed in detail here below.
Construction and Characteristics of the 1326 Family
Stator Windings of 1326 Servo Motors
The material and construction of stator windings impact motor life, efficiency, cooling systems, etc. In other words, careful construction of stator windings is very important. Currently, the sinusoidal winding technique, being the most successful technique, is used to suppress higher harmonics in the air gap magnetic field so the edges of the MMF are smooth or MMF is as much sinusoidal in shape as possible. 1326 motors also employ this technique for constructing stator winding which makes these motors efficient, paves way for noiseless and smooth operation even at low speeds, and allows heat transfer to the ambient. Furthermore, for thermal overload or overheating indications, this winding has a unique solution. A thermal switch is connected in series in the winding which is normally closed. If the winding temperature goes beyond the stipulated limit, this switch would open a disconnecting winding current and thus bring the motor to halt. Typically, the switch will open at 150 °C and closes when the temperature goes back to 90 °C to 100 °C.
To keep losses low and winding safe, its insulation is also paid heed to. Allen Bradley has used an insulation system for windings of this 1326 servo motor family which is UL recognized.
Rotor of 1326 Servo Motors
For a more quick and accurate response of the motor, after getting the control signal, the use of magnets is preferred over the use of reluctance action or induction. Therefore, rotors of 1326 servo motors are also using high-energy permanent magnets for the generation of flux and quick response. To keep motor costs low while maintaining good performance standards, ferrite magnets are used. Different stack lengths of magnets are made available for these motors.
Voltage Classes
For several families or series of servo motors from Allen Bradley, voltage classes are 200 and 400 volts. And those motors operate at 220V and 440V approximately. However, when it comes to 1326 servo motors, they have voltage classes of 460V and 380V. This corresponds to their use and application (note these motors are exclusively for factory use).
Holding Brakes for the Motors
Allen Bradley has designed 1326 servo motors with integral holding brakes. These brakes are spring set brakes that have options of 90V DC (with codes ‘A4’, ‘A5’, ‘A7’) or 24V DC (with codes ‘K4’, ‘K5’, ‘K7’) coils. A4, A5, and A7 with 90V DC brake have 8.1Nm, 13.6Nm, and 45.2Nm holding torque respectively. Similarly, K4, K5, and K7 with 24V DC brake have holding torque values 8.1Nm, 13.6Nm, and 45.2Nm respectively.
To obtain 90V DC voltage for brakes, the brake power supply (code ‘1326-MOD-BPS) is there which converts 115VAC to the needed DC voltage level. This power supply is a modification kit. It has a single-phase, full-wave rectifier in its circuitry. This rectifier has a surge suppressor for safe operation and is screw-mounted. One rectifier (in other words one power supply) can power up to 4 brakes.
For 24V DC brakes, the user can use a power supply that will give 24V DC output with the current ranging between 0.88A to 1.2A.
The brake in 1326 servo motors keeps the load at rest. Moreover, it can also provide limited braking torque in the case of an emergency. Users of this servo motor are suggested by Allen Bradley to ensure that the brake is not energized and de-energized more than 90 times in an hour when it is serving as a parking brake. Because in such a situation it might pose harm.
Feedback Signals and Resolver
For an efficient and precise response of the motor after getting the input signal, controllers need to get position or velocity feedback or calculate estimates of these parameters. In 1326 servo motors, Allen Bradley has used a brushless resolver (standard) which feedbacks position, velocity, and commutation information to the controller. Resolvers installed in servo motors come in single-turn (code ‘S’) or multi-turn (code ‘M’) configurations.
Motors with single-turn configuration give two million counts in one revolution to provide the precise position of the rotor. On the other hand, motors with the multi-turn configuration give one million counts in one revolution and the absolute position of the rotor in 4096 revolutions. This is to provide a reference position upon the start-up of the machine.
There exists no on-board electronic circuitry rendering the machine more rigid and sturdy in harsh environments. This makes the system tolerate relatively higher temperatures and more vibrations.
Encoder-installed 1326 servo motors are also an option.
For obtaining feedback signals, sealed cables are provided by the manufacturer (details in cables section).
These motors are IP65 or IP67 compliant (depending upon the presence of shaft seal). If one tends to use an encoder or resolver mounted externally, then the motor loses IP65 and IP67 rating compliance.
In the accessories package of 1326 servo motors, a feedback mounting adapter kit is also included. These kits are of 8 different types. Each type of kit includes a feedback device mounting adapter, as well as mounting hardware. Allen Bradley warns its buyers that in 1326 servo motors, one shouldn’t use a feedback adapter mounting kit if a high-resolution encoder is used for feedback purposes. Some of these entail motor to encoder coupling.
Shaft and Shaft Seal
1326 servo motors have vertical shafts suitable for upward, as well as downward, mounting. To make couplings safe, there is a threaded hole in the face of the shaft. For this servo motor family also, a shaft seal option exists. The use of a shaft seal will make the motor bear rough environmental conditions. It will make the motor dust-tight and enable it to bear water jet pulses while water won’t enter the motor. These shaft seals are made of Viton material, and it is not necessary to disassemble the motor to install this shaft seal. Shaft mounting has options of Std. Inch and Metric.
In the accessory package for this motor, Allen Bradley has also included Shaft Oil Seal Kit manufactured specifically for the 1326 servo motor family (with the configuration number ‘1326AB–MOD–SSV–xx). This kit can be used where the motor shaft will be subject to oil splashes. Anyhow, if the motor shaft will be submerged in oil or other liquids, either partially or totally, then this kit can’t be used.
The presence and absence of a shaft seal impact the compliance with ratings and standards as well. For these motors, an IP65 rating is standard. Anyhow, after the installation of the shaft seal, the equipment becomes compliant with IP67 (depicted with code ‘L’). Being IP67 compliant means that the motor can be submerged in water for half an hour and that this water body should not be deeper than one meter. IP67-rated motors are provided by the manufacturer with a shaft seal installed at the factory and thus they don’t need a shaft oil kit.
Torque Output
1326 servo motors have quite good torque density. These motors are capable of providing 100% continuous rated torque at standstill conditions. If a blower cooling kit is used to keep the motor’s temperature low, then 35% more torque can be obtained on almost all ‘C’ frame motors of the 1326AB family. This Blower Cooling Kit (with the configuration number ‘1326AB–MOD–Mx) comes as an accessory by Allen Bradley. This kit can also be used for motors that have brakes. Moreover, this kit can be filed mounted for 1326AB–Cxx type motors on their rear side. For these motors, rated torque is measured when the ambient temperature for the motor is 40°C, the controller’s ambient temperature is 60°C and windings are at their rated temperature. Typically, peak torque is 200% of the rated torque but it can go up to 300% of rated torque if RMS (Root Mean Squared) torque is equal to or less than the rated torque.
Thermal Management
The construction of these 1326 servo motors is TENV (totally enclosed non ventilated). Therefore, air doesn’t blow from the inner parts of the motor to the ambiance freely. Instead, external fans or blowers are used to keep the temperature low. As mentioned earlier, Allen Bradley provides Blower Cooling Kits as an accessory to keep the temperature under the limit. Furthermore, two thermal switches are attached in series. Upon detection of temperature above the stipulated limit, switches open and interrupt the operation. These switches open if the temperature reaches 150°C and close the circuit when the motor cools down to 90°C - 100°C. One of these switches is rated at 1A and 115V AC while the second one is at 1A and 24VDC.
It must be noted that the 1326 servo motor family is IP65 rated. If the user uses a blower package mounted externally then the motor no longer remains compliant with the IP65 rating.
For these servo motors, the outer structure is extruded which is built with Aluminium which further enhances prospects for better heat discharged into the environment.
Cables and Connectors
Allen Bradley gives the option of three types of cables for resolver feedback and power for 1326 servo motors. These are known as standard cable (flex cable), track cable (multi flex cable), or extended-length cable (ES). All three cables are environmentally sealed. These cables come in lengths up to 30m. While using a 1391B–ES drive or a 1391–DES drive, cables with lengths up to 90m (extended length cable) are available. Allen Bradley warns its users to hang or lay flat all cables 24 hours before installation.
As far as connectors are concerned, for 1326 servo motors, MIL-spec connectors (military connectors) are standard. These are shell-type connectors so the connection is not affected by ambient conditions and equipment could be used in harsh environments also. These connectors are mounted radially with the motor.
Like many other accessories, Allen Bradley provides Junction Box Kit having the catalog number 1326AB–MOD–RJxx, which has a connector mounted axially. This version of the connector allows the user to bring the motor connector axially towards the motor and not radially. This makes one avoid any further wiring also. Anyhow, the use of the Junction Box Kit makes 1326 servo motors lose their IP67 rating.
Memory
Having onboard memory is among the unique features of 1326 servo motors. Motors with both types of configurations (single-turn and multi-turn) have EEPROM (Electrically Erasable Programmable Read-only Memory) memory onboard. This is basically to store configuration information of motor which will save some time upon start-up.
Frame Length and Diameter
1326 servo motors are lettered sequentially corresponding to increasing frame diameters. Like code ‘A’ is for a motor having 4.25 inches frame diameter, ‘B’ for 5.88 inches diameter, and ‘C’ for 7.63 inches diameter. Similarly, for the given frame sizes, stack lengths are represented by numbers assigned sequentially.
Speed Output of 1326 Servo Motors
Allen Bradley’s 1326 family of servo motors can yield a maximum operational speed of up to 5000 rpm. For ES and DES motors, this speed goes as high as 6000 rpm (revolutions per minute). Different operation maximum speed options are assigned alphabetic codes. The codes and respective maximum speeds are mentioned below.
- Code ‘B’ for a standard maximum operational speed of 1600 rpm and 2000 rpm for ES/DES motor options.
- Code ‘C’ for a standard maximum operational speed of 2000 rpm and 3000 rpm for ES/DES motor options.
- Code ‘E’ for a standard maximum operational speed of 3000 rpm and 4000 rpm for ES/DES motor options.
- Code ‘G’ for a standard maximum operational speed of 5000 rpm and 6000 rpm for ES/DES motor options.
Torque speed curves for these servo motors detail motor performance. If a motor and controller running at a specific speed yield 70% of the continuous rated torque, that speed will be designated as the rated speed. Anyhow, at that time, the motor will be running at 25°C, and the controller temperature at 60°C.
Performance Analysis
As already mentioned, Allen Bradley’s 1326 servo motors are used for high-end motion applications. The smart construction of the machine, presence of multiple tools, and high-resolution feedback system enable these servo motors to perform servo applications accurately. More specifically, 1326 servo motors provide 0.0005 inches or 0.0127mm precision balance in total peak-to-peak displacement.
