MELSERVO J3 Selection Guide
The MELSERVO J3 series, which is also referred to as the MR-J3 series, is a Mitsubishi general-purpose AC servo system based on the previous MELSERVO J2 Super series but with more functions and higher performance. It includes a variety of advanced and flexible Rotary, Linear, and Direct-Drive servo motors that help to achieve optimal machine performance. It is also comprised of high-performance servo amplifiers, featuring a unique and powerful control engine for excellent motion control.
Selecting a MELSERVO J3 System
MELSERVO J3 systems provide excellent levels of accuracy, speed control, flexibility, and precision in automated machinery when the correct MR-J3 servo system is selected for a particular application. Unfortunately, selecting the wrong MELSERVO J3 servo system can lead to underwhelming performance, poor accuracy, or difficulty in tuning. So, how can you select the correct MELSERVO J3 system for a specific servo application?
The key to selecting the most ideal MELSERVO J3 servo system for a given task is to correctly size the servo motors and select compatible servo amplifiers depending on the motion requirements of your application. In this section, we’ll discuss the factors to consider when sizing MR-J3 servo motors and when choosing the right MR-J3 servo amplifiers.
1. MELSERVO J3 Servo Motor Selection
The process of selecting the right MELSERVO J3 servo motor for a specific servo application is often referred to as sizing an MR-J3 motor. This process requires evaluating various factors, such as the application requirements, motor capacity, motor speed, motor torque, gear ratio, inertia, and environmental factors.
- Application Requirements
The first step in sizing a MELSERVO J3 servo motor is understanding its application. This requires establishing the application’s motion profile and torque specifications to determine the mechanical demands of the MELSERVO J3 system, such as peak torque, RMS torque, load inertia-to-motor inertia ratio, maximum speed, and maximum acceleration.
Thus, the most critical formulations of any servo application are the relationships between its torque and speed requirements, which essentially determine the size of the MR-J3 servo motor to be selected and its relative force density. To calculate these two parameters (motor size and relative force density), you need to establish several application factors, such as the weight of the payload, speed and distance of the cycle, and cooling/rest between movements, which is referred to as the duty cycle.
- Motor Capacity
Depending on the power requirements of the specified servo application, select an MR-J3 servo motor that will benefit the required output power with a small footprint. MELSERVO-J3 servo motors are available in 200 to 300 VAC and 380 to 460 VAC models, and they are compatible with three-phase and single-phase power supplies.
- Motor Speed
Just as it’s important to know the load’s weight when selecting an MR-J3 servo motor, knowing the speed that’ll be required of the same motor is also extremely essential. Generally, the higher the speed at which a particular servo motor turns, the lower the attainable output torque.
Note: A low magnetic pole count results in a high motor speed and low output torque due to different factors, including back EMF. Therefore, select an MR-J3 servo motor with an optimal number of magnetic poles that can provide the rated speed.
- Motor Torque
Motor speed and torque go hand in hand when selecting a MELSERVO J3 servo motor. Thus, after specifying the motor speed requirements of your application, the next step will be to identify the continuous torque and peak torque required of the servo motor, thus narrowing down which MELSERVO J3 motor is right.
Continuous torque is a time-weighted average of motor torque during a complete revolution. This torque is also known as the Root Mean Square (RMS) torque. To maintain the required motor speed, the RMS torque should be in the continuous region of the motor’s torque-speed curve. Torque-Speed curves are tools used to represent the relationship between motor speed and torque, showing when relative torque and speed can be sustained simultaneously, either intermittently or continuously.
On the other hand, the peak torque is the maximum amount of torque required at any given point throughout the motor’s cycle. The peak torque should ideally fall in the intermittent region of the servo motor’s torque-speed curve since it’s not that sustainable. So, if the peak torque required by a given servo application falls in the torque-speed curve’s continuous region, then the selected MR-J3 servo motor is likely oversized.
In addition, before selecting an MR-J3 servo motor, you need to know its rated speed and rated torque to determine if the given values will meet the specifications of your MELSERVO J3 system. The rated motor torque is the maximum continuous torque the servo motor can produce at the rated speed when functioning normally and without overheating. It falls on the line that divides the continuous and intermittent zones in a torque-speed curve, whereas the rated speed is the maximum speed that the servo motor can attain when the rated torque is available.
- Gear Ratio
Most MELSERVO J3 servo motors have geared systems, but some do not. However, due to the advent of direct-drive MELSERVO J3 motors, geared servo motors in the same series are considered primitive. But, if your servo application requires torque amplification, you may consider using a geared MR-J3 servo motor, as geared systems can be used to amplify the torque capabilities of a servo motor with a low magnetic pole count.
When selecting a geared MR-J3 servo motor, formulate its gear ratio and use it in the standard torque equation to calculate the motor’s actual torque. Then you can determine if the available real torque will meet your application’s requirements.
Select a MELSERVO J3 motor whose inertia is suitable for your servo application. Motor inertia can be quantified as low, ultra-low, medium, or high.
In rotary servo motors, inertia is generated by the payload’s mass and shape when the load and servo motor accelerate or change direction. The rotor of a servo motor possesses a certain amount of inertia whose value is often negligible when compared to the motor’s payload. The load also has its own inertia, which is increased by any friction motion, such as pulley systems or tables.
Note: Inertia can be used as a decisive factor in MR-J3 motor sizing when the torque value is unknown. The inertia ratio is also a key factor that can be used in determining the performance of a MELSERVO J3 system during servo motor sizing.
- Environmental Factors
The condition of the working environment affects the overall selection of MR-J3 servo motors, because if the environmental conditions are not within the recommended range, then the motor performance will be altered. For example, if the ambient temperature is higher than the recommended value, the possible continuous torque will be lower than specified during motor sizing.
When selecting a MELSERVO J3 servo motor, ensure that the specified environmental conditions are as follows:
- Ambient Operating Temperature: 0 to 40 degrees Celsius (non-freezing)
- Ambient Storage Temperature: -15 to 70 degrees Celsius (non-freezing)
- Relative Humidity During Operation: 10% to 80% (non-condensing)
- Relative Humidity During Storage: 10% to 90% (non-condensing)
- Atmosphere: All MELSERVO J3 servo motors should be operated indoors with no direct sunlight. The operating environment should be free of flammable gases, oil mist, dust, or corrosive gases.
- Altitude: 1000 meters maximum
- Protective Structure: MELSERVO J3 series HF-MP, HC-RP, and HF-PP servo motors require an enclosure with an IP65 rating, while MELSERVO J3 series HF-SP servo motors require an IP67-rated enclosure.
To summarize, selecting the right MR-J3 servo motor starts with understanding the servo application, establishing the characteristics of the load to be moved and its motion profile in terms of velocity, acceleration, and position. After which, key requirements, such as the motor capacity, speed, and torque, are established. This significantly narrows down the correct MR-J3 servo motor to choose. Other factors like gearing, inertia, inertia ratio, environmental factors, efficiency, and accuracy should also be considered. The sequence and priority of evaluating these factors can differ depending on the application.
Examples of MELSERVO J3 Servo Motors
HF-JP Series: This MELSERVO J3 series includes medium to large-capacity rotary servo motors with the following specifications:
- Low-Inertia, Medium Capacity Motors:
- Rated Output Power: 0.5kW to 9kW
- Rated Speed: 3000 rpm
- Maximum Speed: 6000 rpm
- These are suitable for frequent acceleration/deceleration and positioning operations, and ideal for printing and food packaging machines.
- Low-Inertia, Large Capacity Fan-Less Motors:
- Rated Output Power: 11kW to 15kW
- Rated Speed: 1500 rpm
- Maximum Speed: 3000 rpm
- These servo motors have a compact size due to the absence of a cooling fan and wiring reduction as a result of adopting a power supply connector. It’s also suitable for frequent acceleration/deceleration and positioning operations and is ideal for large press machines and injection molding. Note: HF-JP703 (4) (B) and HF-JP903 (4) (B) servo motors have a maximum speed of 5000 rpm. The (B) code in the model number indicates that the particular MELSERVO J3 motor is available with an electromagnetic brake.
- Low-Inertia, Medium Capacity Motors:
HF-MP Series: This series includes ultra-low inertia MR-J3 servo motors that are optimal for high-dynamic positioning machine operations with very small cycle times. Examples of these applications include in-circuit testers, printed board hole openers, label printers, and much more.
HF-SP Series: This series has medium-inertia MELSERVO J3 servo motors. These motors can handle a wide range of applications including winders and tension devices, test devices, specialized machinery, and so on.
2. MELSERVO J3 Servo Amplifier Selection
Once you have selected the right MELSERVO J3 servo motor, after determining its voltage and current requirements, you can then select an MR-J3 servo amplifier. As the key information required when selecting an MR-J3 amplifier is the voltage and current specifications of the selected MELSERVO J3 servo motor, these are determined by the motion requirements of the servo mechanism being driven.
To select the right MR-J3 servo amplifier, specify the following:
- Compatible Servo Motors
You should select an MR-J3 amplifier that can be paired with the selected MR-J3 servo motor. Therefore, it is important to list all servo motors in the MELSERVO-J3 series that are compatible with various MR-J3 servo amplifiers. For example, the MELSERVO-J3 servo motors in HF-MP, HF-PP, HA-LP, HC-RP, and HF-SP series can be paired with servo amplifiers in the MR-J3-A and MR-J3-B series.
- Feedback Mechanism
Like all servo systems, MELSERVO-J3 systems also require feedback mechanisms to provide closed-loop operation, as well as detect and correct any errors in the servo motor’s actual position, velocity, or torque. This feedback mechanism can be provided by encoders, resolvers, or Hall sensors. However, regardless of the feedback mechanism used in the servo system, the selected servo amplifier should be compatible with its feedback signal.
By default, all MELSERVO-J3 servo motors are available with an MR-J3 single-turn absolute position encoder that’s rigidly coupled to the servo motor’s shaft. The MR-J3 encoder has a high resolution of 262,144 ppr (pulses per revolution), making it possible to achieve accurate positioning and high-speed stability. The encoder reports the position of the motor shaft (actual position value) back to the connected MR-J3 servo amplifier. The MR-J3 servo amplifier can then control the position deviations of the connected MR-J3 servo motor by comparing the position set-point (command value from the motion controller) and the actual position value provided by the MR-J3 encoder.
Therefore, be sure to select an MR-J3 servo amplifier that is compatible with the feedback signal from the encoder coupled to the selected MR-J3 servo motor. This will ensure that the selected MR-J3 servo drive can process the received feedback signal and communicate it to the motion controller.
- Voltage and Current Requirements
The most basic requirement when selecting a MELSERVO J3 system is that the power from the MR-J3 servo amplifier, which includes the peak current, continuous current, and maximum voltage, should be sufficient to produce the mechanical output (torque, position, and speed) required by the selected MR-J3 servo motor. This is because the operation of MR-J3 servo motors and MR-J3 servo amplifiers is co-dependent.
Therefore, once a specific MR-J3 servo motor is selected for a given servo application, choose an MR-J3 servo amplifier rated for the correct input voltage and with sufficient output current to drive the selected servo motor. You can refer to the torque-speed curves provided by Mitsubishi Electric to determine the voltage and current requirements of specific combinations of MR-J3 servo motors and MR-J3 servo drives.
- Operating Mode
Check the servo control loops available with the MR-J3 servo amplifier you intend to select. Generally, servo control loops are incorporated within servo drives to be used to control velocity, position, torque, or even a combination of the three parameters.
MR-J3 servo amplifiers provide torque control, position control, and speed control modes. The MELSERVO J3 servo system can also operate with the following control mode combinations: Torque/Position, Speed/Torque, and Position/Speed control. Thus, select an MR-J3 servo drive that incorporates the servo control loops or control mode combinations that will meet the motion control requirements of your MELSERVO J3 system.
- Analog or Digital
Determine if your servo application requires an analog or a digital MR-J3 servo amplifier. However, some MELSERVO J3 servo amplifiers, like the MR-J3-A series, can respond to either digital or analog signals. These MR-J3-A servo amplifiers are provided with inputs for pulse (digital) and analog signals. Therefore, these amplifiers can handle multiple applications regardless of whether digital or analog signals are involved.
Select an MR-J3 servo amplifier that supports the communication protocols provided by the connected MELSERVO J3 controller. For the servo drive and controller to communicate with each other, they require a common language/common communication protocol.
Servo drives are available with a variety of communication protocols ranging from basic serial links (i.e. RS-485) to more advanced protocols like DeviceNet or Ethernet network protocols. The choice of the communication protocols to be used with MR-J3 servo amplifiers mainly depends on the data transmission rate required, the presence or absence of master-slave arrangements between multiple servo amplifiers, and in other cases, the type of motion controller being used.
For example, MR-J3-B servo amplifiers available with SSCNET III bus communication network are designed for operations that include MELSEC System Q motion controllers. The SSCNET III communication system is an optical bus network that enables the exchange of serial data via light-based optical fiber optics. This optical communication system offers high data transmission speeds and is not influenced by Electromagnetic Interference (EMI) signals from other electrical devices.
- Integrated Safety
Ensure that you select an MR-J3 servo amplifier that complies with mandatory safety standards, such as EN/ISO 13849-1 and EN/IEC 62061. It would also be advantageous if the selected MR-J3 servo amplifier includes several safety functions like the Safe Torque Off (STO) feature and Safe Stop 1 (SS1) function.
- Mounting Options
Select an MR-J3 servo amplifier whose mounting specifications will be appropriate for your servo application. For industrial applications, most servo drives are either PCB-mounted or panel-mounted. Panel-mounted servo amplifiers are often installed in a control cabinet, in which they can be externally cooled and protected from extreme environmental conditions.
- Environmental Specifications
The MR-J3 servo amplifiers have a variety of environmental specifications. It is highly recommended that the user of this device follows all the recommendations set by the manufacturer when it comes to the area surrounding the MR-J3 servo amplifier. The environmental specifications of this servo amplifier include:
- Ambient Operating Temperature: 0 to 55 degrees Celsius (non-freezing)
- Ambien Storage Temperature: -25 to 60 degrees Celsius (non-freezing)
- Relative Humidity: 10% to 90% (non-condensing)
- Atmosphere: All MR-J3 servo amplifiers should be operated indoors without direct sunlight. The operating environment should be free of flammable gases, oil mist, dust, or corrosive gases.
- Altitude: 1000 meters maximum
- Vibration Level: 5.9 m/s (0.6 g) maximum
- Protective Structure: MELSERVO J3 servo amplifiers require an enclosure with an IP00 rating.
Available MELSERVO J3 Servo Amplifiers
MR-J3 servo amplifiers are available with an extensive power output range of between 100 watts to 55 kilowatts. Depending on the model, these servo amplifiers are suitable for single-phase (when the output power is 700 Watts or less) and three-phase power supplies rated at 200 VAC to 230 VAC, or three-phase power supplies rated at 380 VAC to 480 VAC. The available MR-J3 servo amplifier models are classified in terms of power range and input voltage, as outlined below:
- Output Power Range
- Series MR-J3-A/B: 100 watts to 37 kilowatts
- Series MR-J3-A4/B4: 400 watts to 55 kilowatts
- Series MR-J3-T/T4: 100 watts to 55 kilowatts
- Input Voltage
- Series MR-J3-A/B/T: 200 VAC to 230 VAC at an input frequency of 50/60 Hz
- Series MR-J3-A4/B4/T4: 380 VAC to 480 VAC at an input frequency of 50/60 Hz
The skill of selecting optimal MELSERVO J3 servo systems for various servo applications can be improved with practice. While some applications may require specialized functions from specific MELSERVO J3 servo motors and servo amplifiers, this article has provided key factors that can guide the selection of a general-purpose MELSERVO J3 system. But when in doubt, verify your selection results with the manufacturer or distributor.