VPL Servo Motors

VP Low Inertia Servo Motors

VP Low inertia motors come from Allen Bradley’s Kinetix VP series. To elaborate, Allen Bradley’s Kinetix VP series servo motors are grouped into four subseries:

• Kinetix VPC continuous duty servo motors, which provide continuous torque, as well as power.
• Kinetix VPL Low inertia servo motors, which have significantly low rotor inertia.
• Kinetix VPF food-grade servo motors are meant to be used in the food industry.
• Kinetix VPH hygienic motor for applications where there is hygienic wash-down.

In this article, VP Low inertia motors will be discussed in detail.

Kinetix VP Low Inertia Servo Motors

VP Low inertia motors are highly efficient motors that are developed according to a drive system rating so that their size remains compact. These motors are structured in a way that enables them to use just one cable for powering up the motor, motor braking, and feedback. These motors are to deliver good dynamic performance. Their dynamic performance is based on technology proven by MP Low inertia motors. Briefly, these motors have low inertia, leverage usage of just one cable bringing simplicity and safely ensuring ease of use, and have a high torque density. Advanced winding techniques, usage of rare earth magnets, and low weight are a few notable characteristics of these motors which will be also discussed in detail.

Design and Characteristics of VP Low Inertia Servo Motors

Stator Design

As mentioned earlier, VP Low inertia motors are designed on technology proven by MP Low inertia motors. It implies that advanced winding techniques are employed in the stator design. This winding ensures less winding losses and proportionally reduced weight of the machine. Winding insulation is also made carefully to keep the losses low.

The stator in VP low inertia motors is equipped with three-phase winding to generate stator flux. The windings in these motors have a voltage class rating of 200V or 400V. The winding of the motors affects the maximum speed.

Rotor Design

The rotor design of Allen Bradley’s VP Low inertia motors is as unique as the stator design. These motors are brushless, which means it is low maintenance and has a safer operation in a wide range of conditions. Furthermore, these motors are AC synchronous motors. Synchronous action in combination with high efficiency suggests the presence of magnets. Allen Bradley has used highly efficient high-energy rare-earth magnets for rotor flux generation. VPL servo motors with different stack lengths of magnets are available. For now, 1, 2, 3, 4, and 6 stacks of magnets are used for VPL servo motors. 1 stack of a magnet is usually 1 inch thick. The magnet stack length affects the rated speed, power, and torque. On the rotor’s shaft end, there is a threaded hole.

Single Cable-based Technology

VP low inertia motors of Allen Bradley have come with ease of connectivity and thus simplicity in terms of usage. These motors need just one cable to complete all their connections at once. The ultimate result is the elimination of hardware components. Communication is purely digital and two-wire which comes integrated into the power cable of the motor.

For constructing continuous flex, as well as non-flex, cables, TPE (Thermoplastic elastomers) material is used. To be more specific, PVC (Polyvinyl chloride) material is used for non-flex cable construction and Halogen-free PUR for continuous flex cables. This special cable is from the Kinetix-2090 series by Allen Bradley.

Unique construction incorporating special characteristics is designed specifically for drive systems compatible with VP low inertia motors. Therefore, the use of third-party cables or construction of one’s cable using a connector kit no longer remains an option as was the case for MP Low inertia motors.

Connector

VP Low inertia motors have just one connector as a single cable connection is to be established. This connector is a SpeedTec DIN connector. This connector can rotate up to 325 degrees.

Feedback System

For accurate and highly sensitive speed and position-related applications, the position of the rotor is essential to be known. This data is fed back to the controller for better motor performance. These servo motors have high-resolution feedback which is made through high-performance encoders. The installed encoder could perform through a single turn or multiple. Moreover, they can be categorized based on resolution. The detailed classification of available encoders for VPL servo motors is as follows:

• 18-bit resolution or 262,144 counts per revolution. These encoders have electromechanical build-up, eliminating the need for a battery.
  • The single-turn encoder has a code C configuration and gives absolute position feedback in just one turn.
  • The multi-turn encoder has a code P configuration code and gives absolute position feedback of the rotor in 4096 rotations.
• Absolute digital encoders with multi-turn feedback rated at SIL 2 having 18 or 23-bit resolution.
  • Encoders with 23-bit resolution give 8388608 counts in one revolution. These multi-turn encoders (represented with code ‘O’) also provide absolute position. These encoders also have a secondary safety channel of 12-bit. These encoders are available only for motors of frame sizes VPL-B165xx, VPL-A/B130xx, VPL-A/B115xx, and VPL-A/B100xx.
  • SIL 2 rated encoders could also be with an 18-bit resolution giving 262,144 counts per revolution and providing absolute position in 4096 turns. These encoders (code W) also have a secondary safety channel of 9 bits. Anyhow, this encoder doesn’t come with all VPL motors. Instead, it is available just for motors with frame sizes of VPL- B075xx, and VPL-B063xx.

Motor Braking

There are two braking options for VPL servo motors: 24V DC brake and no brake. In the configuration code, 24V DC braking is denoted by code ‘4’ and no brake option is represented with code ‘2’.         

DC brakes in these low inertia motors are holding brakes i.e., these brakes will keep the rotor to a standstill unless applied torque crosses the holding torque for that motor. Brakes in different motors have different release and engage times. This example explains these details further. For motor catalog number VPL-A/B0753, when the brake is engaged, the maximum backlash is 30 arc minutes while holding torque is 3.0Nm, coil current at 24V DC is 0.567 to 0.693A, the brake release time is 66ms, brake engage time is 42ms, and the brake rotor inertia is 0.0000142 kg-m².

Frame Size

VP series low inertia motors have 6 different options for frame sizes, which is also the bolt circle diameter (BCD). The available frame size options and respective codes in the configuration numbers are given below:

• ‘063’ for 63 mm
• ‘075’ for 75 mm
• ‘100’ for 100 mm
• ‘115’ for 115 mm
• ‘130’ for 130 mm
• ‘165’ for 165 mm

Rated Speed of VPL Servo Motors

Different motors in the VPL servo motor series have different rated speeds. This speed does not exceed an 8000 rpm (revolutions per minute) limit. 9 different speed options and their respective codes in configuration numbers are given below:

• 'A' for 1500 rpm
• 'B' for 2000 rpm
• 'C' for 2500 rpm
• 'D' for 3000 rpm
• 'E' for 3500 rpm
• 'F' for 4500 rpm
• 'M' for 6000 rpm
• 'T' for 6750 rpm
• 'U' for 8000 rpm

Shaft Seal and Shaft Key

VPL servo motors have two factory options while referring to the shaft seal. A motor could come standard means without a shaft seal (code ‘A’ as the last digit of the configuration number) or it could be equipped with a shaft seal (code ‘S’ in the configuration number). Furthermore, this shaft could be a smooth shaft means without a shaft key (code ‘K’) or have a shaft key (code ‘J’). Shaft seals for these VPL motors are made using nitrile material. Allen Bradley notifies its buyers that shaft seals are prone to wear so the owner must inspect and maintain the seal frequently. It is suggested to replace the shaft seal every 3 months. In any case, this period should not go beyond 12 months. Allen Bradley has made Shaft seal kits available to help and ease inspection and maintenance of shaft seals. These kits also include lubricants so the wear of seals could be reduced. For different motors of this series (different catalog numbers), different shaft seal kits are available e.g., for motor VPL-A100xx and VPL-B100xx, MPL-SSN-A3B3 is the suitable shaft seal kit.

The availability or non-availability of shaft seal also affects the environmental standards, the machinery should comply with (See relevant paragraph for details).

Continuous and Peak Stall Torques

VP Low inertia series motors are designed using advanced technologies. This makes them lightweight. Their design is compact as well (lower size). Moreover, there comes the factor of low inertia as the series name indicates. All these characteristics refer that these motors have high torque density. Different motors from this series can provide continuous stall torque in the range of 0.46Nm to 33Nm. While peak stall torque ranges between 1.33Nm and 79Nm. Figures show that peak torque is 2 to 3 times the continuous torque. Not all torque options exist for all frame sizes or both voltage classes (200V and 400V). For example, VPL-A0631E from 200V class has 0.46Nm continuous stall torque and 1.33Nm peak stall torque. Similarly, from the 400V class, VPL-B1654B has 32.97Nm continuous stall torque and 79.3Nm peak stall torque.

Motor Rated Output/Rated Power Output

VP Low inertia motors of Kinetix drives have high power density like their high torque density. The rated output for these motors ranges from 0.19kW to 5.55kW. The power output of a motor is directly proportional to its speed and torque. For example, VPL-B0631T and VPL-B0751M (both from the 400 class) have an 8000 rpm rated speed. However, the continuous stall torque of the former is 0.46Nm and that of the latter one is 1.01Nm. Accordingly, the rated output of the former is 0.31kW and that of the latter one is 0.54kW.

Compatible Servo Drives

To make the system efficient, economical, and compact, the compatibility of different components of the system with one another is crucial. Allen Bradley has designed these VPL servo motors to work well with Kinetix 5700 and Kinetix 5500. In other words, windings are designed to match with electrical specifications of mentioned drive series.  Anyhow, it does not mean that Kinetix 5500 or Kinetix 5700 will not be suitable for other motors. Instead, Kinetix 5700 goes well with Kinetix MPL, Kinetix MPM, Kinetix MPF, Kinetix MPS, Kinetix VPL, Kinetix VPC, Kinetix VPF, Kinetix VPH, Kinetix VPS, Kinetix HPK, Kinetix MMA, and Kinetix RDB. Similarly, Kinetix 5500 can be accommodated with several families of motors.

Environmental Specifications

VPL servo motors are used in a range of environmental conditions. To prolong the life of these electrical components and ensure safety against electric bursts out and other dangers, their construction must include measures for safety. Therefore, to keep VP low inertia motors protected from dust or water, Allen Bradley has made them comply with recognized environmental standards. The presence or absence of a shaft seal determines which standards will be complied with.

Motors having optional shaft seals are IP66 standardized. However, it must be noted that these motors can bear heavy wash down but can’t be submerged into the water completely. Moreover, users are restricted to use such cable connectors for these motors which are environmentally sealed. On the other hand, standard motors or motors without shaft seals comply with IP50 at a minimum.

Applications of VPL Servo Motors

Because VP servo motors have low inertia, high torque density, and small sizes, they are used for applications where these characteristics add to the value and provide ease of functioning. These motors can also operate with maximum loads regardless of the factor if it is radial shaft load or axial shaft load (limits mentioned for all motors of this series for both types of loads).  For example, these motors are used in the packaging industry where preciseness and neatness have become the norm, so VP Low inertia motors perform well. Similarly, these motors are used for electronic assembly. The compactness of these motors with low inertia ensures that operation will be performed accurately. At bigger levels, these motors are used in material handling, converting, and automotive applications.

Certifications

To gain credibility and more confidence in VP Low inertia motors, Allen Bradley has got a UL certification for the VPL servo motors. These Kinetix VP motors meet CSA and UL standards that are applicable or relevant for the rotary machines.