Category

Applications and How-Tos

Electromagnetic Tooth Clutches – How they Work

KEB Tooth clutches are electrically engaged and provide three times more torque than friction clutches.  This video shows how they work.

 

 

 

 

VIDEO TRANSCRIPT

KEB is a leading manufacturer of electromagnetic tooth clutches.  Compared to the typical friction clutch, a tooth clutch has the advantage of offering roughly 3 times more torque in the same diameter.

 

This is particularly advantageous for medical and printing machinery, where space is of concern.  This video describes how a KEB tooth clutch operates.

 

First, lets get acquainted with the main clutch components: The primary drive shaft typically contains a stationary electromagnet which is fixed with a flange or torque tab.  A rotor is fixed to the primary driving shaft with a key or other connection.

 

Next, an armature is riveted to a flat spring.  The flat spring is then riveted or screwed to a hub – or in this case, a pulley which is connected to a secondary shaft with a belt.  Both the rotor and armature face feature a fine tooth profile, which mates them together.

 

Here’s how the tooth clutch works: With the primary shaft stopped, the clutch can be engaged by supplying the electromagnet coil with the nominal DC voltage.  This creates a magnetic field that passes through the clutch rotor and armature.

 

The magnetic field’s force is large enough to deflect the flat spring and pull the armature across a small pre-set airgap towards the rotor face.  The toothed profile of the armature and rotor mate allowing the pulley to turn synchronously with the primary shaft.

 

It should be noted that the tooth clutch should be engaged when the shafts are stationary or the tooth profiles could be damaged.

 

When electrical power is removed from the coil, the flat spring returns and pulls back the armature.

 

Without the toothed connection, the two shafts rotate independently.

 

 

You can read more about KEB’s Tooth Clutches at our Tooth Clutch product page.

 

More posts in this series

 

Electromagnetic Clutch

This video describes how KEB electromagnetic clutches operate. KEB clutches are electrically engaged and allow a friction connection between two shafts.
 

Servo Motor Brakes

KEB offers power-off spring-set servo motor brakes designed specifically for servo motor applications that require fail-safe braking.
 

Permanent Magnet Brakes

KEB’s permanent magnet brakes are commonly used in servo motor and robotic applications because they are compact and provide zero backlash power-off braking.

VFDs for Single phase applications

VFDs and Single Phase AC motors

 

My first job out of school was with a motor manufacturer doing technical support.  Being in the midwest, we had a lot of farmer and agricultural customers.  

 

Their applications ranged from running fans, pumps, elevators, agitators, augers, conveyors, etc.  The farm installations often didn’t have access to three phase power and had to make do with single phase 230V.  We sold a lot of single phase motors into these installations.  

 

Many of the single phase motors were relatively large – between 5 and 15Hp.

 

single phase farm duty motor

Farm Duty Single Phase motor

 

There are a number of challenges to operating large single phase motors.  A frequent question from these customers was, “Can I add a VFD to my single phase motor?”.

 

This post outlines the use of VFDs in single phase applications  – why a person would want to add a VFD, sizing considerations, a rough cost comparison, and the advantages a VFD offers.

 

The problem with line feeding single phase motors

One challenge to operating large single phase AC motors from the line is the starting current.  A 10HP single phase motor will pull 38A nominal (at 230V).

 

But that motor (NEMA B design) will pull 6-8 times the nominal current when starting up – or 234 Amps!  

10HP single phase motor data

A 10HP single phase motor will pull 234 Amps starting current @ 230V.

 

 

 

This is enough to make the power companies take notice, especially if there are multiple motors starting up at the same time or the electrical service to the remote farm is near capacity.

 

To be fair, the problems associated with high starting currents will also affect a line-fed three phase motor.  But in the case of a three phase motor, a person can easily add a VFD.  One benefit of VFD operation is that while ramping up the motor speed, it will limit the motor current.  

 

The problem is that a VFD cannot operate most single phase motors – at least not at reduced speeds.

 

 

The centrifugal switch in capacitor start Single Phase motors

There are a few different designs of single phase motors.  I’ll highlight the one I have seen most in industrial applications – ones with a capacitor start and centrifugal switch.  The design uses a capacitor network that is in the motor circuit at low speeds.  The capacitors help develop torque at zero speed and get the motor started in the correct direction.

 

single phase motor wiring diagram

Common single phase motor wiring diagram – with capacitors and centrifugal switch

 

Once the motor is spinning and has inertia, a centrifugal switch opens and the capacitor network is disconnected from the primary motor windings.  The speed at which the switch opens happens before reaching the nominal slip speed.

 

For this reason, it is not a good idea to use a motor designed for 60Hz on a 50Hz main.  At least not without swapping out or adjusting the centrifugal switch.  It could be possible, that the switch never opens when running at 50Hz.  This could damage the capacitors or overheat the motor windings.

 

A similar concern would be using a VFD to control the speed of a single phase motor.  Lowering the speed would effectively keep the capacitors in the circuit and potentially damage the motor.

 

 

Single phase input to VFD

So if you can’t use a VFD with this design of single phase motor, what is the solution?  The answer is to input single phase to the VFD.  The VFD can act as a phase converter and output three phase to a three phase motor.  

 

There are some considerations, particularly with sizing.  Some VFDs are designed and rated to input both single and three phase.  Check with the VFD manufacturer but you’ll see something like this in the manual which denotes both phases.

 

With larger drives, the ratings tend to only indicate a 3 phase input.  Single phase input is possible but a derating is likely needed.  

 

Let’s look at a VFD application with three phase input running a 10HP motor.  Let’s assume there aren’t any losses and PowerIN = PowerOUT.  The input current and the output would be the same.  

 

Three phase vfd input

The input power is distributed through three phases

 

Now, take that same application running a 10HP motor but with a single phase input.  PowerIN = PowerOUT.  Except all the power at the input is now going through one conductor instead of three.  Effectively, there is a √(3) factor applied to the single phase input current compared to the three phase current.  

 

single phase VFD input power

All input power (current) flows through one conductor

 

 

Again, some drive sizes already have input rectifiers over-dimensioned and can inherently handle the increased single phase input current – this should be reflected in the power stage ratings.  For larger HP applications, the net result is the drive might need to be upsized to handle the larger input current.

 

As a rule of thumb, we suggest rounding up and assume the single phase input current will be double that of the three phase input current.

 

Finally, it is also a good idea to use a 5% line reactor when applying single phase input power to a drive.  During power-up, the drive will have an inrush of charging current to the unit.  The 5% reactor will help reduce the peak charging current and protect the VFD’s input rectifier stage.

 

 

What about cost

There is a price premium for single phase motors, especially larger HP motors.  Doing a quick calculation of that same 10HP motor from above and the single phase variant is a +60% cost premium.  My guess is that some of the added cost is due to the added parts of the capacitor network and switch.

 

The other part of the cost is because larger single phase induction motors are more of a specialty compared to the three phase types.  

 

Add in the additional cost of a VFD/reactor but also subtract out the premium for the single phase motor.  I think you’ll find the cost of adding a VFD is much less than you think.

 

Why not just use a rotary phase converter instead of a single phase VFD?

A phase converter is certainly an option.  It will convert single phase power to three phase power.  But that is all it does.  It does not offer the many advantages that a VFD will offer.  

 

There is also a similar argument to be made on the cost of a phase converter.  The phase converter will likely not save much, if any money, compared to a drive.

 

 

Advantages of using VFDs in single phase applications

A user will benefit going from a line fed motor to a VFD controlled motor.  They will be able to optimize the motor speed for the process.  Maybe this means slowing the conveyor down during loading instead of completely shutting off the motor.  Lightly loaded motors can also be oversped to speed up processes.

 

A user will also benefit from the energy savings due to the VFD.  Especially quadratic load applications like fans and pumps.   The higher duty the application, the more savings there will be.  Add some basic feedback to the application like a temp or humidity sensor and the VFD can be wired to regulate a process.  KEB’s F5 even has a built-in PID controller so the entire process can be regulated inside the drive – removing the need for an external PLC or control

 

One advantage with VFDs that is often overlooked is all the protective functions they have that detect abnormal situations.  

  • Over/Undervoltage – Automatically shutdowns when there is a brownout or power surge.
  • Motor Overheat – This option requires a thermistor or motor temp sensor.  It protects the motor investment and is a good idea for expensive motors, difficult to service motors, and high ambient temperature applications.
  • Overcurrent protection – This could detect an abnormal fault like a shorted motor winding and shutdown.

 

There are many more protective features for sure, but you get the idea.  

 

What experience do you have operating VFDs with single phase inputs?  Add comments below.  Contact us, if you want to discuss an application.

 

87Hz motor control for Delta Wye VFD operated motors

Across KEB’s line of AC induction motors and variable frequency drives, a small trick allows for the output of 1.74 times more power from the same IEC-motor size. This blog post describes how the “87Hz control” works and the benefits it has to offer.

 

Delta/Wye Motor Operation

Delta/Wye motors (Δ/Y) are wound to allow for two different voltage connections. Depending on how you have the motor connected, the motor can be connected for either 230V or 400V.  This type of winding is typically supplied by European motor manufacturers so the stators are often rated for 50Hz but 60Hz variants do exist.

 

Delta or Wye motor connection for 87 Hz Characteristic

Typical motor terminals that can be jumpered out for either a Delta or Wye connection

 

The basic Volts/Hz Motor Curve

During standard open loop operation, the VFD defines a ratio between the rated voltage and rated frequency. For example, when wired for the delta connection this ratio is: 230V/50Hz = 4.6 V/Hz. Thus, whenever the command frequency to the drive is increased by 1 Hz, it increases the output voltage to the motor by 4.6 V.  With a 6-pulse VFD, the output voltage is limited by the supply voltage.  So once a motor reaches its rated frequency and voltage the output voltage plateaus because there is no more voltage available due to what is supplied to the drive.

 

Typical 230V and 400V motors

The Torque and Power Curves

Induction motors controlled by a constant V/Hz ratio will operate in a constant torque mode. During operation, the torque will remain constant as the motor is accelerated up to its rated frequency.  This constant torque will be equal to the motor’s nominal rated torque.

 

Power = Torque * Speed.  So unlike torque, the power is not constant during acceleration but increases proportionally with the applied frequency (speed).

Torque and Power Curves_230V motor

Beyond its rated frequency, the motor enters what is known as the field weakening range. This occurs when increasing the frequency while keeping the supply voltage constant.  The supply voltage is constant because there isn’t any more available voltage from the drive.  When operating in this range, the behavior of the power and torque changes.  In this range, as the frequency increases, the power remains relatively constant while the torque decreases inversely proportionally to the frequency.  This results in the torque dropping rapidly relative to a small increase in the frequency.

 

In some applications it would be nice to be able to operate in this field weakening range without experiencing the drop in torque.

 

The 87 Hz Characteristic

For systems that need to maintain constant torque even in the field weakening range, the 87 Hz characteristic can be used. This allows the Δ (230V/50Hz) connected motor to be operated using a 400V inverter without saturating the motor.

How does it work?

During standard operation, providing 400V to the delta connected motor would be too high. Because of this, the corner frequency must be shifted to maintain the same V/Hz ratio.  If the constant V/Hz line from the 230V/50 Hz delta connected motor is extended, it eventually reaches 400V/87 Hz (400V/87Hz = 4.6 V/Hz = 230V/50Hz). This allows for constant torque up to 87 Hz instead of just 50 Hz and for a power output increase by a factor of 1.74.

Adding 87 Hz Characteristic_230V motor

What are the advantages?

Using the 87 Hz characteristic offers multiple, related, benefits. During this operation, the motor is able to maintain constant torque up to 87 Hz with a 400 V supply.  The motor can also supply 1.74 times more power compared to the standard 230V/50Hz operation with the delta connection.  Because of this, it is possible to get away with using a smaller IEC-motor size while maintaining the same required power and torque.  It may also be possible to avoid using an external fan.

Graph_Advantage of 87 Hz Characteristic

What are the disadvantages?

Power is power and the inverter must be sized appropriately.  This means you would use a larger inverter than normally matched with the motor.  The inverter will need to be a 400V class inverter but would be sized on the 230V current ratings.

 

What if my motor and supply are rated for 60Hz?

The 87Hz motor control has been commonly used in Europe with 50Hz mains.  For this reason, the name “87Hz” stuck.  However, the same method also works on a 60Hz rated Delta-Wye motor with 60Hz mains.  However, the operating point with the higher frequency becomes 104Hz (60Hz*1.74) instead of 87Hz..

 

 

The 87 Hz characteristic is a simple and easy solution to provide more power and torque with the same IEC-motor size. Interested in learning more about the 87 Hz characteristic or the benefits it could offer your application?

Contact an Applications Engineer at KEB America today.

Spindle motor control with KEB drives

With over 200,000 installed spindle drives, KEB has earned a reputation as the worldwide spindle drive leader.  This post describes some of the reasons KEB is preferred by our CNC, woodworking, and robotic customers.

 

 

 

Spindle Motor Control

KEB drives can run both induction and permanent magnet spindle motors through the adjustment of a drive parameter.  KEB’s robust motor control algorithms mean it can run a variety of different motor designs from all major spindle motor manufacturers.  Basic applications can utilize V/Hz control.  The advantage of V/Hz is its simplicity and ease of commissioning.

 

Closed loop applications can be solved using KEB’s dual channel encoder interface.  Many feedback formats are supported including: Incremental TTL/HTL, Resolver, EnDAT 2.1/2.2, Hiperface, etc.  Tool change and orientation functions can be programmed in the drive.  This possibly allows the PLC or controller to be removed from the system.

 

Closed loop drives offer the additional feature of torque limits.  Different sets can be programmed which allows a number of different torque limits to be set to match the motors operating characteristic – ensuring that the motor does not become overloaded.

 

KEB’s unique SCL™ and ASCL™ (Sensorless Closed Loop, Asynchronous Sensorless Closed Loop) control technology can be used to provide closed loop performance without the need for encoder feedback.

 

 

Spindle Performance

Newer drive platforms like the S6 feature a fast current control loop of 62.5µs.  This provides excellent spindle motor performance and, ultimately, a better final product.

 

KEB drives are offered in switching frequencies up to 16kHZ with output frequencies up to 1667 Hz for high-speed applications.  This allows motor speeds in excess of 100,000 rpm while keeping motor noise and heating to a minimum.

 

KEB drives are offered in sizes from fractional horsepower up to 1000 Hp.  For 3 phase installations, 230VAC and 460VAC voltage classes are available.  Additionally, a single phase 230VAC variant is offered.

 

 

Ethernet On Board

Although KEB drives support a variety of different communication protocols like Ethernet/IP, Powerlink, and Profinet  –  we have standardized on EtherCAT.  EtherCAT communication offers excellent real-time performance, is an open technology with many vendors and members, and offers tremendous value for its performance.

S6 with On-board EtherCAT

EtherCAT is well suited in demanding, high-performance applications.  For example, the S6 platform supports a 500 µs scan time for up to 8 parameters (up to 32 bytes).  The EtherCAT process data can be used to send a home or orient command to the drive.  This can be used for a basic home start or for a tool change.  The S6 drive will use the zero pulse from the encoder to position the spindle for a tool change.

 

Combivis Wizard for easily configuring EtherCAT Process Data

 

Positioning can also be done over EtherCAT.  The desired position (position counts either relative or absolute) can be written to the drive directly over EtherCAT.  Alternatively, predefined positions can be stored in the drive and the PLC can select which position the system should move to and send that signal over EtherCAT.

 

 

Functional Safety

Along with the benefits of EtherCAT mentioned above, KEB drives also offer functional safety options.  Safe-Torque-Off (STO) is offered as standard.  More advanced Safe Motion functionality according to ISO 13849 is available, including: SS1, SS2, SOS, SLS, SLP, SLI, SDI, SSM.

KEB Drive Safe Motion – Per IEC 61800-5-2

 

One advantage for moving Safe Motion into the drive is that the drive’s high power does not need to be removed in certain situations.  An example would be when an operator opens the machine tool door to clear debris.  Traditionally, all power would be cut from the drive to the motor does not unintentionally start.  But this requires that operator waits so the drive bus capacitors can discharge and recharged again.

 

With KEB’s SIL3 Safe Motion functions, this same functionality can be achieved through our Safe control card and 24V inputs.  High power remains connected which ultimately allows for machine operation.

 

See why KEB is the spindle drive leader, discuss your application with a KEB engineer today.

Replacing clutch and motor brake rectifiers with KEB rectifiers

This post serves as a guide for replacing a DC clutch or brake rectifier with a KEB rectifier.

motor brake rectifier

KEB UL listed rectifiers for DC brakes and clutches

 

First, why would anyone want to replace their clutch or brake rectifier with a KEB rectifier?  Here are some reasons:

  1. The brake rectifier is a passive device and relatively easy to change out. We’ll outline the process below.
  2. KEB rectifiers are industrial grade and better quality than those supplied with most OEM products.
  3. KEB rectifiers are UL listed – #E308765. Check your current rectifier product – most are not listed.
  4. KEB rectifiers are stocked and ready to ship.

 

So what are the good rectifier candidates to replace with KEB?  Basically, any brake or clutch using a DC coil.  Here are some examples:

  • Gearmotor or motor brakes from suppliers like SEW Eurodrive, Nord, and Sumitomo
  • Clutches from suppliers like Warner and Ogura.
  • DC brakes from suppliers like Lenze, Intorq, Stearns, and Precima.

 

 Process for crossing over clutch or brake rectifier:

1.  Download the KEB Rectifier manual

First, for reference, you’ll want to download the KEB rectifier manual which has all the dimensions and ratings.

 

2.  Double check that the brake or clutch has a DC coil

AC brakes use solenoids and do not need rectifiers.  For more information, check out this post which compares DC vs. AC brakes.

 

3.  Verify if you need a half-wave or full-wave rectifier

Check the incoming AC voltage and your rated DC electromagnet voltage.  Decide which type of rectifier will give you the correct output voltage.

 

Please note, this post only applies to standard half and full-wave rectifiers – not overexcitation types which have a time-based component.  Also, 24VDC magnets do not need this type of rectifier and will typically be supplied from a 24V power supply.

 

Half-wave rectifiers will output:

VDCOutput = VACInput * .45

 

 

Full-wave rectifiers will output:

VDCOutput = VACInput * .90

 

For reference, here is a grid showing the different KEB rectifiers by Type and Voltage rating:

keb brake rectifier grid

KEB rectifier grid

 

 

4.  Verify the rectifier voltage and current rating

The listed VACInput on the rectifier should be greater than the incoming AC voltage you are connecting to it.  See pages 4 and 5 of the KEB rectifier manual for the max input voltage ratings.

 

 

The amp draw for the magnet can be calculated if the voltage and coil wattage are known.

ICoil = WCoil / VCoil

 

Make sure the amp rating of the KEB rectifier is greater than the amp draw of the electromagnet coil.  This is also listed on pages 4 and 5.

 

5.  Verify how the current rectifier is being switched – AC or DC side switching

For more information on the wiring of AC and DC side switching, see page 6 of the KEB rectifier manual.

 

If DC side switching is used, then you must select one of KEB’s switches rated for 500VAC or less. They will start with either a 02 or 04.

 

Brake rectifier - DC side switching

The middle terminals of this switch allow DC-side switching

 

6.  Verify physical dimensions

Finally, verify that the rectifier will physically fit in your terminal box or electrical cabinet.  See page 5 of KEB rectifier manual for dimensional info.

 

 

 

That’s it!   If you have any questions about crossing over your rectifier, feel free to contact a KEB engineer today.

Remote Access to Allen Bradley Rockwell PLCs

A few common questions I get from customers: Does the C6 Router support Ethernet/IP, DH+? Can the C6 Router connect to my ControlLogix, MicroLogix, CompactLogix, etc.? Can I get remote access to Allen Bradley PLCs?

 

The answer to these questions is yes!

 

The C6 Router used in conjunction with Combivis Connect software can setup a secure end-to-end VPN connection to your Allen Bradley PLC’s.

 

 

This blog post will review the steps needed to establish remote access with a C6 industrial router to a Allen Bradley PLC and RSLogix software.

 

Step 1: Internet Access to Router

 

In order for Combivis Connect to setup a VPN connection, the C6 router must have internet access. The router acts as a VPN server and assigns the user PC an IP address within the VPN network ensuring a direct end-to-end connection using secure TCP/UDP ports and SSL/TLS protocol.

 

This can be accomplished two ways. Either by configuring the WAN interface or configuring the modem with a standard SIM card.

 

Remote access allen bradley WAN config allenbradleyconnect_modem

 

Step 2: Configure LAN Interface

 

Assign the LAN interface an IP address within the local PLC network. All Allen Bradley PLC’s using EtherNET/IP, DeviceNet, ControlNet, etc. belonging to the subnet of the LAN interface can be reached via the VPN tunnel.

allenbradleyconnect_lan

 

Step 3: Serial Port Configuration

 

Allen Bradley PLC’s using serial protocols such as DF1, DH+, or DH485 can also be remotely monitored and programmed. Combivis Connect uses a virtual serial adapter to map to the physical serial port of the C6 router. Select the correct port setting.

allenbradleyconnect_serial

remote-connect-rockwell-slc-500

The C6 Industrial Router supports remote connection to legacy PLC-5 and SLC 500 series PLCs as well

Step 4: Register Router to Domain

 

Before the C6 router can be connected, too, the router must be assigned to the domain of Combivis Connect. Assign the router a name, and apply the settings.

domain_registration

 

Step 5: Connect to C6 Router

 

 

Once the router has finished rebooting, the router can be connected to. Simply select the Connect button to establish a connection. Once the router is connected the all Allen Bradley PLC’s can be accessed via the VPN tunnel.

 

vpn_connect

 

Step 6: Remote Access with RSLogix

 

At this point RSLogix can go online with the PLC and program in desired Controller operating mode.

 

remoteconnect_allenbradley

 

 

 

Remotely accessing Allen Bradley PLC’s is easy and reliable using Combivis Connect and the C6 Router. There is no lengthy setup process or complicated communication driver setup to access your Allen Bradley PLC’s.

 

Are you interested in remotely accessing your Allen Bradley PLC’s with a C6 Router? Contact a KEB controls engineer today to discuss.

 

Derating induction motors

KEB Servo Motors

Synchronous motors like KEB’s Servo Motors can be adjusted for derated speeds easily

When looking at different applications that use variable frequency drives (VFDs) and motors, there are some that require the motor to be run at slower speeds than the rated motor speed. One example of an application that might require this would be a relatively slow elevator that doesn’t need to run at the full motor rated speed. Sometimes motor manufacturers will provide a set of motor data with the derated application data included. For certain applications with VFDs this derated motor data is fine to enter into the drive, but for others it can cause major issues, particularly derating induction motors.

 

For permanent magnet gearless motors (synchronous motors), derating the motor data in the drive is acceptable. These motors run at their synchronous speed, so there is a linear relationship between the motor rated speed, frequency, and voltage as well as between torque and current. If derated motor data for a permanent magnet motor is entered into a KEB F5 drive, then the motor tune function can be completed as usual and the drive will operate the motor as intended. The motor tune will still measure the different properties of the motor correctly and create a motor model internal to the drive that is used to control the operation of the motor at various speeds.

 

Helical bevel gearmotor - K unit

Induction motors need additional configuration to run at derated speeds

Induction motors (asynchronous or squirrel-cage motors) behave differently than permanent magnet motors. Due to the design of the motor, it operates at a rated speed less than the synchronous speed, by a difference known as the slip speed. Because the motor has this slip speed, there is not a linear relationship between the motor speed and frequency (based on the number of motor poles). The slip is what allows an induction motor to produce torque. When running an induction motor, the drive provides magnetizing current to the motor in order to maintain the magnetic field that provides the necessary torque. The drive also provides phase current to the motor that allows the motor to run. If there is an application where a derated rated motor current value is entered into the drive, the drive will correspondingly limit the magnetizing current in the motor model internal to the drive. This causes the motor to run with more slip to compensate for the lower magnetic field, which actually results in a higher operating current. This may seem counter-intuitive that lowering the motor rated current in the drive would result in a higher operating current. However, due to the lower magnetizing current in the motor model, derating the motor data for an induction motor would lead to an increased phase current draw.

 

The best thing to do with an induction motor that is intended to operate at a lower speed while using a KEB VFD is to enter the actual nominal rated motor data into the drive, including the full load rated motor speed (not the synchronous speed), as opposed to the derated application data. With this data, the drive can create an accurate motor model without limiting the magnetizing current.   In this case, the drive must be sized according to the nominal motor rated current.  This is due to a limit of 110% of inverter rated output current which can be entered for motor rated current.  So, it may not be possible to downsize the drive based on derated motor current for induction motors.

 

If you need assistance with derating an induction motor, give us a call or email and one of our engineers can help you get things running smoothly.

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