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KEB Technology

Brakes for electric linear actuators

Due to their precise and smooth operation as well as their high power density, it is obvious why electric linear actuators and servos have paved the way for superior control in many industries that require critical positioning.

 

KEB has acknowledged this trend and has had great success with the implementation of permanent magnet and spring applied brakes within our customer’s actuators and servo motors.

 

 

brake for linear actuator

KEB Spring applied brake for an actuator

 

The linear actuator applications vary widely but can include military, food and packaging, and medical machinery. In such industries, there is significant demand for accuracy.  Missing a precise position or failing to hold a load in place without slippage could yield catastrophic results.  Additionally, these machines are often times holding heavy and expensive equipment so incorporating a brake is often necessary for added security.

 

Brake selection for linear actuators

KEB typically supplies 2 different brake products for electric actuator applications.  They are Permanent magnet brakes and spring applied brakes.  Both are power off brakes but each brake has its own advantages.

 

Permanent magnet brakes (see how they work) offer better torque density.  They have roughly 33% more torque in a given diameter, compared to spring-set brakes.  So if a small brake diameter is required this style is preferred.  As technology advances and machines become intricate, space often times is constrained, as a result, permanent magnet brakes have become a more attractive option to many customers.  Permanent brakes also offer zero backlash performance and are well suited for high-precision applications.

 

Permanent Magnet brake

Permanent Magnet Brakes offer zero backlash performance

 

 

Although the P1 permanent magnet brakes are power-off, they are not spring applied or considered failsafe.  For critical applications like lifting or hoisting, KEB spring-set brakes are preferred (see how they work).  KEB’s spring-set brakes provide reliable brake engagement in the case of loss of power or even excessive friction lining wear.

 

electromagnetic brake

Spring-set brakes provide power-off braking for critical axes

 

Standard features for spring applied and permanent magnet brakes include:

  • Insulation class: Rated for ISO class F.  Class H is possible if needed.
  • Protection: Rated at IP 20 protection however most customers typically locate brakes within the actuator housing yielding protection ratings up to IP 69.
  • Coil voltage: Most commonly 24VDC but all common voltages are available (12, 24, 48, 105, 205).
  • Certifications: CSA and UL listing is possible for both designs.
  • Hand Release*: Optional manual hand release (spring applied only).  Note the hand release option does limit the IP rating as the brake release handle needs to travel outside the housing.
  • Dust boot: Optional dust boot for IP44 protection with exposed brake, this can be used with hand release (spring applied only)
  • Dimensions: Most metric/imperial bore sizes possible with keyways.

 

Custom Features

Beyond our standard product features, we can also offer custom features to accommodate the linear actuator.  The advantage we offer is that we will dive into your application as well as your specific actuator design and assembly to ensure we have an optimized solution.  The primary location to mount a brake is often times within the actuator or servo housing on the back shaft of the motor.

 

This can be a hassle as there is often limited space and minimal flexibility on the brake profile that will fit within this section of the housing.  By investing the time to understand our customer’s product we often times find small tweaks that we can do to our standard products to allow optimal fitment to accommodate the available real estate.  Similarly, we can pinpoint custom features to implement that will ease or enhance assembly on the customer’s end.

 

Spring set actuator brake

Spring-set brakes provide power-off braking for critical applications

 

Some custom features we have accomplished in the past include:

  • Customer specified cable connectors.
  • Specified torque window.
  • Custom mounting or flange to accommodate actuator housing.
  • Custom package to accommodate actuator housing.
  • Encoder mounting holes on brake magnet.
  • Extended hub collar to provide sandwich stack up assembly within actuator housing.
  • Cutouts along the side of the brake profile to allow wire passage.

 

Why Choose KEB?

Simply put, experience matters.  KEB has been manufacturing brakes for 40+ years.  During that time we have successfully partnered with many of the leading linear actuator companies to develop reliable high-performance actuator brake solutions.

 

One reason KEB has earned our reputation in this corner of the industry is the flexible offering of solutions we have.  Beyond our standard product line, we are willing to provide custom solutions to accommodate customer needs.  This could be something as simple as special connectors or an adapter plate.  Or it could be something with added complexity like a custom magnet with boosted magnetism.

 

We have full design and manufacturing capabilities at our US location in Shakopee Minnesota and are willing to take on custom solutions to ensure we supply the right products for the specific application.

 

electromagnet design software

KEB utilizes advanced magnetic simulation software to optimize the product design and performance

 

Local engineering and production do not mean expensive – we work with our customers to offer economical solutions which meet the application requirements.

 

Obviously, a locally manufactured product helps us to be responsive.  KEB America has successfully replaced a number of different European, Indian, and Chinese brake competitors.  10+ week leadtimes with sea freight shipments does not cut it in today’s demanding marketplace.

 

local brake manufacturing

KEB’s local manufacturing and QA allows responsive service

 

We’d love an opportunity to work on your next design project – Contact us today!

 

Working with OMAC to promote better standards

For more than 45 years KEB has been perfecting the development of automation and control solutions for several vertical industries, including packaging machinery.

 

The catalog of products we offer can be used at nearly any point in the packaging line, which is why KEB America aims to be more than a supplier of a single component. We are a complete solution provider for the packaging industry. Our commitment to creating the best solutions for our customers can be seen not only in our top-quality, German-engineered hardware solutions, but the powerful software which programs our control products.  For this reason, KEB has joined the OMAC group and has begun the development of a PackML solution.

 

OMAC and PackML promote standardization in packaging machinery software

 

Standardizing solutions for automation and control

Building an application system that uses modern automation and information analysis should be a priority for competitive manufacturers. However, many companies face significant delays or even road blocks when building their packaging line because machines simply cannot communicate with each other or with the end user in a useful way. KEB recognizes the issues that come up with system integration, and has joined with OMAC in an effort to make fully-networked lines a reality for more companies.

 

Since 1994, the Organization for Machine Automation and Control has been working to provide manufacturers and their customers with the tools to optimize their production and profitability in a competitive market. OMAC brings together end-user manufacturers, OEM machine builders, system integrators, technology providers, and non-profit/government agency organizations to address common roadblocks to success and create standards of performance across their product lines.

 

 

PackML

KEB has joined the list of technology providers whose products follow the standards set by OMAC, and will be developing software to meet PackML requirements.

 

PackML, or Packaging Machine Language, was created to encourage interoperability between hardware and software vendors supporting the packaging industry. It does this by standardizing machine states, modes, commands, and data. The end result is improved development time, better reliability, and easier maintenance and monitoring.

 

 

KEB as a technology provider

HMI LC, programmed with OMAC standardsBy committing to PackML standards KEB is ensuring our library of products will be suitable for both new and existing packaging lines. If you’re building a new line from the ground up, our sales engineers can walk you through our full catalog and select the products and versions best suited to your business goals. Existing lines can benefit from KEB’s decades of experience and top-of-the line technology with products that seamlessly integrate with any of the other technology providers in the OMAC.

 

Implementing PackML standardized state diagrams on the KEB HMI will provide operators with a familiar interface, great for fast training and support. Programming a KEB PLC is done with programming tags and key performance indicators that are already defined so communication between equipment is quick to set up and easy to configure.

 

At KEB we’re committed to being a full solution provider for our customers. If you have any questions about how KEB products with PackML built in can benefit your packaging line, be sure to contact our knowledgeable sales engineers.

 

You can also chat with us in person at the PackExpo in Las Vegas – booth 6282. We’d love to meet with you and share our packaging machinery solutions.

dV/dt Motor chokes for long VFD cable runs

Ask someone at a motor repair shop and they will tell you VFDs are hard on motors.  Bearings fail due to VFD-caused bearing currents. Over time, insulation fails due to corona discharges.  One scenario that is particularly stressful to motors is when the motor and VFD are mounted a large distance away from each other.

 

Long cable runs can lead to high voltage rises (or “dV/dt”) at the motor and can contribute to premature motor failure.  This post describes VFD-related standing wave voltages and how to protect against them by using KEB dV/dt filters.

 

dvdt chokes

 

What are dV/dt Spikes?

Most commercial AC VFDs use a technology called pulse-width-modulation (PWM) to simulate a 3-phase AC sinusoidal voltage output. PWM operates by rapidly turning the drive’s output insulated-gate bipolar transistors (IGBTs) on and off – Thereby modulating the DC bus voltage of the drive. When the IGBT is closed, the voltage at the VFD’s output terminals rises to that of the drive’s DC bus.

 

IGBT rise time

Figure 1 – IGBT rise/fall time

The change in voltage is not instantaneous but actually, ramps up to the DC bus level over a given time (TRISE). The rate at which the voltage increases is referred to as the dV/dt rise time and is a characteristic of the transistor design.

 

Motor Cabling & Reflected Wave

The cabling between the drive and the motor has a characteristic impedance which is dependent on the cable length and the physical properties of the cable material. The motor cabling acts as a transmission line and propagates the drive’s output voltage to the motor. If the impedance of the motor and cabling are not matched, a wave reflection will occur at the motor load – this results in a voltage
overshoot or “ringing” at the motor terminals and a reflected wave back to the drive.

IGBT overshoot

Figure 2 – IGBT with overshoot voltage (as measured at motor terminals)

 

In a worst-case scenario, the reflected wave could be added to the fundamental waveform coming from the drive resulting in a significantly higher voltage at the motor terminals. Longer motor leads have larger impedances, ultimately increasing the voltage at the motor leads. For this reason, it is a best to mount the motor and drive as close together as possible.

 

In practical terms, what does this mean?  Let’s look at a typical VFD installation with a 25Ft. cable length and no dV/dt choke.  At the motor terminals, we see a voltage of 988V even though the DC bus on the VFD is only 675V.

vfd voltage spikes

Figure 3 – No choke, 25 Ft. Leads. Peak motor voltage = 988V

 

With the same setup, we now increase the motor leads from 25Ft. to 75Ft. in length.  We are now seeing a max voltage at the motor terminals of 1,326V – double that of the DC bus!

vfd standing wave

Figure 4 – No choke, 75 Ft. Leads. Peak motor voltage = 1,326V

 

dV/dt effects on motor operating lifetime

In short, voltage peaks from high dV/dt break down a motor’s insulation and shorten the motor’s operating lifetime. Most 3-phase AC motors produced today are “inverter-rated” and utilize wire and insulation rated to withstand peak voltages of at least 1600V.  However, even if the dV/dt spikes never exceed the 1600V insulation rating, the repeated exposure to the spikes over the motor’s lifetime will stress and weaken the insulation.

 

Over time, the motor insulation system could breakdown – resulting in a phase-phase or phase-ground short in the windings and a catastrophic motor failure.

 

 

What VFD applications should I look out for?

Long cable runs

Any application that has long cable runs that cannot be avoided or shortened.  MRL elevator applications where the motor is mounted in the hoistway.  Submersible pumps.  HVAC equipment.

 

As a rule-of-thumb, KEB recommends the use of a dV/dt choke for runs greater than 40 feet.

 

 

High Switching Frequencies

KEB drives offer selectable switching frequency.  Higher switching frequencies offer some application advantages.  First, it reduces the audible noise made by the VFD which is important in sensitive installations like an MRL elevator near the penthouse or with a theatre hoist.  Second, higher switching frequencies provide the motor with a higher quality current waveform which results in lower motor losses and less heating.

 

Related to the discussion of dV/dt, it is important to note that higher switching frequencies require that the transistors turn on/off more times over a given period of time – Thereby, exposing the motor to an increased number of high voltage peaks.  Operating at 16kHz will expose the motor to twice the number of voltage spikes compared to 8kHz.

So drive applications using higher switching frequencies should be especially concerned about dV/dt.

 

480V Installations

Because the drive’s peak output voltage is directly related to the DC bus level, the dV/dt spikes will naturally be larger in 480VAC installations compared to those in 230VAC installs.

Extra precaution should be taken to mitigate the dV/dt spikes in 400-480VAC installations.

 

dV/dt Mitigation & Filters

If the above items cannot be mitigated, a person should consider using a KEB dV/dt filter (or dV/dt choke) which will decrease the IGBT rise time and reduce the peak voltages at the motor. A dV/dt filter is placed directly at the output of the drive and limits the rate of change of the voltage (dV/dt) to a level characteristic of the filter design.

 

dvdt choke

KEB dV/dt motor choke

 

It is important that the filter is placed as close to the output of the drive as possible so the voltage peaks are not propagated through the motor cabling. Unless the motor and cabling impedances are matched, the standing wave reflection could still occur but the negative effects are dramatically minimized by the filtering of the dV/dt spikes.

 

Let’s return to the previous example, and place a dV/dt choke on the drive with the 75Ft. cabling.  The peak voltage is reduced from 1,326V to 951V – a 40% reduction.

vfd voltage peaks

Figure 5 – With dV/dt choke, 75 Ft. Leads. Peak motor voltage = 951V. A 40% reduction in peak voltage.

 

KEB dV/dt Filters

KEB filters were designed specifically for demanding VFD applications – They offer high performance but are commercially cost-effective. Some of the design features of the KEB dV/dt filters are:

 

Feature Benefit
Low Inductance Design Does not skew the motor model like common load reactors; can be used with PM and induction motors
Operable up to 16kHz Well suited for high-frequency VFD applications
Minimal Insertion Loss Efficient design with minimal power losses
Small Footprint Requires less panel space – Lower system cost
Reduced EMI Limits radio frequency emissions (> 250kHz)

 

 

Do KEB dVdt chokes sound right for your application?  Contact us today to discuss with a KEB application engineer.

What is Functional Safety over EtherCAT, FSoE?

With a number of new KEB Functional Safety over EtherCAT (FSoE) products on the horizon, this post is a primer on FSoE and why it is important to machine builders.

 

Failsafe over EtherCAT PLC

 

Functional Safety over EtherCAT

If you haven’t seen FSoE yet (sometimes called Failsafe over EtherCAT), you will start seeing it more and more.  FSoE is a communication protocol that was developed by the EtherCAT Technology Group.  The goal was to design an industrial communication bus that would be suited for use in safety applications – up to an IEC 61508 SIL3 level.  To put this into perspective, this means the communication bus would need to operate in excess of 100,000 years without an undetected error.

 

Each FSoE node receives a unique address (16-bit) and the safe data with checksum are encapsulated in the EtherCAT telegram:

FSoE Telegram

 

Overall, the Failsafe over EtherCAT protocol has a number of different features that help detect an error in the communication, including:

FSoE error detection

 

Each FSoE slave is handled with a state machine.  Upon start-up the slave must go through the state machine in order to set any of the safe bits.  In the event of an error, the state machine is reset and the master must re-validate the connection before changing any of the safe bits.

FSoE State diagram

 

There is a lot more technical information – Members of the EtherCAT Technology Group can download a full copy of the specification at, https://www.ethercat.org.

 

 

So why should machine builders care?  Here are 5 Reasons.

 

  1. FSoE is certified to an IEC 61508 SIL3 level

The protocol was designed with a number of different features (watchdog timers, checksums, etc.) that enhance security and allow the detection of errors.

 

Very importantly, the FSoE protocol was independently certified by TÜV Süd Rail GmbH to the IEC61508 SIL3 level.

 

This is relevant because it has been evaluated by a 3rd-party safety agency and carries the appropriate certification.  When coupled with similarly certified safety hardware, the machine builder will have a much easier time having their overall machine certified for functional safety.

 

  1. FSoE is an open protocol published by the Ethernet Technology Group (ETG)

ETG hit a home run with EtherCAT.  By making the technology open and accessible it encouraged many vendors to develop EtherCAT products.  The machine builders benefitted because they had access to many different vendors and products.  The end user benefitted with high-performance technology and lower costs due to many competitive offerings.  It has been a win-win for everyone.

 

Similarly, FSoE is open and published by the ETG.  Increasingly, more automation companies will develop FSoE-based products and the ecosystem will continue to grow.  Both machine builders and end users will benefit with a wide selection of products and vendors.

 

This is not always the case with competing safety protocols on the market today.  Some protocols out there are closed and proprietary.  Any control solutions that are developed will tie a machine builder into that one vendor’s hardware and programming tools.  This introduces risk as you are tied to one vendor.

 

In short, because Failsafe over EtherCAT is open, it gives machine builders an increasing number of product options from a number of different vendors.

 

  1. FSoE can be implemented with other networks

FSoE works with standard Ethernet hardware and network cables so it can be used with other PLC vendors and with other industrial protocols.  For example, it would be possible to have a machine controlled with an Allen-Bradley or Siemens PLC but the safety functionality and safety IO is handled by a FSoE system.  The FSoE safety network could even be used with a mix of different control types – like on a large packaging line, for example.

 

This gives a machine builder flexibility.  Perhaps customers in one geography specify a PLC type from Vendor A.  Another geography specifies Vendor B.  2 machine variants can be offered but the FSoE safety control can be used across both designs.  This is a big advantage considering the huge time and cost required to certify the functional safety of the machine.

 

  1. Failsafe over EtherCAT saves wiring costs and time

Another really big advantage of FSoE is that much of the discrete safety wiring can be replaced with a network cable.  Manufacturers of rental and mobile machinery will benefit greatly from this.  The design of the safety system is largely done in the software and by using certified FSoE hardware.

 

There are a number advantages to replacing the discrete wiring:

  • Reduction in wiring time
  • Reduction in wiring errors
  • Cleaner panel layout
  • Better noise immunity

 

  1. FSoE allows for Functional Safety in the Drive (Safety Drive Profile)

    KEB has a deep EtherCAT drive portfolio.  FSoE drives are one of our differentiators.  By design, the FSoE control word allows for advanced Safe Motion functions (according to IEC 61800-5-2).  This means it is possible that a FSoE slave like an inverter can handle advanced safety functionality like Safe Limited Speed or Safe Limited Positioning.

    Safety Drive Profile, ETG 6100.1

    Safety Drive Profile, ETG.6100.1

     

    By default, the below functions are configured in the drive’s safety control word.  Additional Safe Functions are possible with manufacturer-specific bits.

    FSoE Default Safety Control Word

    FSoE Default Safety Control Word

     

    The safety function in the FSoE drive can be triggered locally with inputs or it can be enabled via the FSoE bus.  Finally, the status can be communicated back to the FSoE master with the drives Safe status word.

     

    I’d be interested in hearing any thoughts regarding Failsafe over EtherCAT or safety communication buses – advantages, disadvantages….  To talk to a KEB engineer, contact us today!

Elevator Regenerative Drives – How They Work

 

This video shows how elevator regenerative drives operate and how they can capture an elevator’s energy and put it back on the building power.

 

Full transcript

 

Elevator Regen Drives – How They Work

 

When lifting a fully loaded car in a traction elevator application, electrical power is delivered from the building utility to the elevator system.   However, when descending, that same fully loaded car will regenerate energy.  In other words, the stored energy in the mechanical system is converted back into electrical energy.

 

Historically, for VFD applications, this energy was shunted across a braking resistor and dissipated as heat.  This resulted in two problems: First, the heat represented wasted energy.  The costs to a building owner could be significant depending on the size, duty, and number of elevators in the building.  Second, the additional heat in the machine room often resulted in additional cooling costs.

 

There is a better, greener alternative.  KEB’s R6 Line regenerative drive replaces the traditional braking resistor and can be used alongside the elevator drive.  When an overhauling situation exists, the R6 regen unit goes active and commutates energy back onto the building to be consumed by other loads, such as lighting or HVAC.

 

The R6 is very compact and is available in capacities up to 500 Amps.  The smaller units can be used on both 208V and 460V installations and automatically detect the mains voltage and frequency.  The R6 units require little adjustment and are easy to use.  They feature internal DC fuses and programmable I/O.

 

For applications that need to meet IEEE 519 power quality standards, passive KEB harmonic filters can be used to meet the most stringent levels.

 

In addition to saving energy, the R6 line regen units save money too.  For efficient gearless systems, the ROI can be less than 2 years.  KEB offers an online calculator that can be used to estimate the savings a building owner could expect to achieve.

Go green with KEB’s R6 Line regen unit.

 

To learn more about KEB R6 elevator regen drive, contact us through our Contact Us page or give us a call.  We’d be happy to answer your questions.

 

More information: 

Elevator Regen Calculator

Does Elevator Regen make sense for my building?

 

EtherCAT Relay IO Module from KEB

 

The EtherCAT Relay IO Module is the newest addition to the KEB Automation catalog of products. The Relay IO module combines a pilot relay with an IO module, providing the functions of two blocks on a DIN rail in the space of one. At only 25mm wide, the Relay IO module is a great space-saver in any installation cabinet.

 

Full transcript

KEB’s EtherCAT relay module is the most recent addition to our I/O family.

 

The module is used to interface with both 120 volt and 230 volt AC field wiring. Typically a power contactor is signaled by a pilot or control relay. Traditionally the pilot relay is connected to an I/O module which then receives signals from a push-button, a sensor, or via the PLC. The signal going through the pilot relay will trigger the contactor to turn the load on and off. KEB’s relay module combines the function of an I/O module and DIN-mounted pilot relay.

 

When multiple loads are required you save significant space on the DIN rail by removing pilot relays and consolidating up to eight loads into a single module. Similar to other KEB I/O blocks the relay module measures only 25mm wide and has pluggable connectors. It is DIN rail-mounted and mechanically locks into other modules for a secure connection.

 

The I/O signals communicate from the C6 Smart to the relay module through a high-speed EtherCAT backbone. KEB’s EtherCAT relay module features eight Form A normally open contacts. The contacts are rated two amps each for inductive loads and five amps each for resistive loads.

 

The relay module is UL-listed and available for immediate sale.

To learn more about KEB and our EtherCAT Relay IO Module visit the Contact Us page on the website. Fill out the contact form or simply give us a call and we’d be happy to answer your questions. Thanks.

 

dV/dt filters – FAQ

This post outlines some frequently asked questions regarding KEB’s dvdt filters. When to use them, how they work, and approximate costs.

 

dvdt filters

 

Q. When do I require a dV/dt filter (choke)?

A. KEB strongly recommends the use of a dV/dt choke for all VFD installations where the motor is located 40 ft. or more away from the drive and electrical cabinet. Using a dV/dt choke in closer installations is recommended but optional.

 

 

Q. Can I use KEB dV/dt chokes with drives from other manufacturers?

A. Yes, in fact, this is a differentiating feature of KEB filters. Because the KEB dV/dt chokes have a low inductance they shouldn’t affect the drives ability to measure the motor parameters during an auto-tune or skew the internal motor model.

 

 

Q. Can I use a standard load reactor to mitigate high dV/dt on an installation with a long cable run?

A. It is not recommended. The high inductance and capacitive coupling found in these chokes will still result in high dV/dt while limiting the motor’s peak torque during acceleration.

 

 

Q. Can I use KEB dvdt filters for both PM servo and induction motors?

A. Yes. The KEB dVdt chokes effectively limit the voltage transients in both applications.  Notably, they do not negatively affect the operation of either motor by adding significant inductance.

 

 

Q. Can I use the KEB dV/dt chokes for either 230V or 480V applications?

A. Yes. The chokes are designed to be used for voltages up to 550VAC.  They are sized by the current requirements of the application.

 

 

Q. How much does a KEB dV/dt choke cost?

A. The dV/dt choke is typically a fraction of the cost of a motor – maybe less than 5%. This represents a small investment up front to prevent a costly repair or replacement at a later date.  Applications using specialty motors, motors from vendors overseas, and motors that are difficult to service and reach should take extra care to protect the motor investment.

 

 

For more information on dV/dt and how KEB filters work, see this post.

 

To discuss with a KEB application engineer, contact us today.

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