KEB manufactures armature-actuated brakes (not caliper or drum-style brakes) which are well suited for smaller motors used in residential elevator, MRL, and dumbwaiter applications.
This post provides an overview of KEB brakes and why they are well suited for elevator applications.
Spring applied operation
KEB’s Combistop brake product is electrically released and spring-applied. Sometimes these brakes are referred to as “failsafe brakes” because they will engage when power is removed. This is the type of operation a designer will want to use in lifting, hoisting, or safety-related applications.
Designed and manufactured in the USA
A lot of the advantages KEB brings to the table are because our brakes are engineered and produced outside Minneapolis, MN. This means that we are able to use our core brake technology and design features as the application requires.
From a supply chain standpoint, this is also a big advantage to our North American customers. Local manufacturing means that leadtimes are typically shorter and the product is not originating overseas.
One product feature that KEB is able to offer is noise-reduced operation. A loud ‘clunking’ noise or a rattle from the brake as the elevator car levels is not desireable.
Various design features are incorporated into the KEB brakes which reduces the noise levels. Overall, this provides a much more pleasant experience for the elevator passenger, especially in a residential or MRL elevator application.
There are actually several different noise reduction options at various performance/cost levels depending on what our customers require.
NPT fitting for conduit
KEB brakes can be fitted with an NPT fitting which allows the electrical conduit to be run and connected directly to the brake. Additionally, if needed, we can offer our brakes with extended leads to be fed back to the power supply or elevator controller.
Typically, an elevator brake must have the ability to be released even without power (consider a power outage). For this, KEB brakes can be fitted with a manual hand release. When the hand release is pulled back, the brake disengages and the shaft is free to rotate.
When released, the hand release returns to its location and the brake engages. This operation is sometimes referred to as a “dead-man’s brake” and is an important feature for safety applications.
KEB also offers a microswitch feature on our brakes. A microswitch is typically used to provide feedback to the controller that the brake has actually engaged. It adds an element of safety as a brake confirmation is needed before power is cut to the motor.
It also has operational benefits. When incorporated with the controller and various brake timers, a microswitch can reduce lining wear and allow for a much smoother brake transition.
KEB typically also provides mounting flanges with our brakes. The flange serves two purposes. Firstly, it provides a suitable friction surface for the friction lining. This means the surface finish is designed to KEB’s required specifications. Secondly, it can act as a heatsink if the brake is performing a significant amount of work.
KEB can design and provide custom flanges as well. A popular option is to use a C-Face flange which can then be mounted onto a C-Face motor end bell.
Double C-Face option
A spring-set variant we also provide for elevator applications is our Double C-Face brake. The advantage of the Double C-Face brake is that it can be paired together with an off-the-shelf NEMA C-Face motor. Overall, the solution can be more cost effective especially when an encoder device is added to the equation. Motors with a brake and encoder are not cheap.
KEB Double C-Face brakes are offered up to 256TC frames and are available with different magnet voltage options.
Gear(motor) with brake
The final configuration where our brakes get used in elevator applications is when paired with our integral gearmotors. The KEB gearmotor product is designed in Germany and assembled here in the US. The product offering is extremely flexible and has a lot of product options like encoders, shrink disc mounting, and brakes.
The brakes are again what set KEB apart from other manufacturers. We are able to offer all of these high-performance brake options (noise reduced, microswitch, etc.) which are very well suited for elevator applications.
And it all comes together packaged with our gearmotor product. So these are savings to elevator manufacturer in the form of reduced labor and installation time.
KEB’s Energy Recovery Systems are interesting to highlight because they combine a lot of our unique leading-edge technology. The systems also highlight the breadth of KEB products and our ability to integrate them together to provide a comprehensive turnkey solution.
For the scope of this post, an Energy Recovery System (ERS) or Energy Conversion System (ECS) is an electronic system that controls turbomachinery and converts energy from some process. The process involves converting high-frequency electrical power to something usable on the mains or building power (e.g. 50 or 60Hz). Typical processes could be geothermal, air separation, or waste heat recovery.
KEB’s Energy Recovery System functions like this. A KEB load drive controls the speed of the generator. The set speed is controlled via a master control system. When the process gas is introduced, the load drive regulates the generator speed. As energy is returned to the electrical system, the Active Front End (AFE) is able to return energy to the building power or utility.
A big highlight of the system is the simple control for the process operator. Rather than trying to regulate the pressure and flow of the process gas, the KEB load drive regulates the generator speed.
High-speed motor/generator applications are demanding. Control instabilities and imperfections that are masked at low speeds can become critical at high speeds. KEB has a lot of experience running high-speed asynchronous and synchronous generators.
The turbomachinery used in energy recovery processes typically use specialty high-speed generators. The generators are usually equipped with special magnetic bearings or airfoil bearings and can spin in excess of 100,000 rpm. The advantage of using high-speed generators is that they are extremely compact, efficient, and have high power density.
KEB drives are capable of outputting frequencies up to 1600Hz which is required to run these generators/motors. But it is not only the listed output frequency and hardware that separates KEB from other drive vendors. KEB’s SCL™ algorithm provides better speed and torque regulation than commonly used V/Hz control. Another advantage is that SCL does not require encoder feedback – this is difficult to acheive at high speeds.
SCL-optimized generator control creates less rotor heating and increased energy output — this benefits the motor manufacturer and the user.
SCL offers a lot of flexibility with parameter adjustments as well – this allows the KEB system to work with a variety of different generator types and designs characteristics.
Another reason KEB is well suited for high-speed drive applications is that of our experience designing and supplying sinewave filters. A sinewave filter cleans up the drives PWM output and provides a sinusoidal waveform to the motor winding. This also helps reduce motor heating which is critical to a high-performance system.
Air-Cooled or Water-cooled
KEB offers both air and water cooled drives. Many times, there will be liquid cooling in the system already. Liquid-cooled drives offer a number of advantages especially if the systems will be installed at high altitudes or in high ambient temperatures.
Air-cooled versions are often preferred for their simplicity. The point is that KEB can provide both solutions, depending on the application needs.
High Power – with scalable offerings
The purpose of installing an Energy Recovery System is to lower overall energy usage and save the facility money. This means that smaller systems will likely not provide sufficient ROI and warrant the investment. And at some power threshold, the systems become economically feasible.
KEB does high power well. This means the energy recovery concept can be easily scaled across different power ranges. With optimization, it becomes easier to make a business case for investing in an energy conversion system.
KEB offers Active Front End (AFE) technology with low harmonic distortion (THiD). AFE is of interest to those looking to generate power back to the mains. The clean generated power will not create issues for other electrical loads and the power factor can even be compensated as needed.
Full Panelized System
KEB offers a standalone drive panel that includes all the drive, filter, and control necessary to control the motor-generator.
A C6 HMI LC provides drive diagnostics and the ability to make parameter adjustments. The HMIs ship with a CONNECT runtime which means the systems can provide remote access. This gives the possibility to provide remote maintenance and future PLC upgrades.
The HMI LC can also act as a network gateway. This means the KEB panel can tie in with the processes master control via another network protocol like Modbus, EtherNet/IP, or Profinet.
KEB can provide individual components but this is a case where a lot of thought has already been put in and engineered into a complete turnkey solution.
The KEB conversion system includes a grid protection relay and an EMI filter to mitigate high-frequency noise. Also, there is provision to detect an emergency situation and then safely disconnect the system. These are features that would need to be considered and implemented anyway. In this case, they are already engineered by KEB into a system that can be easily integrated into the process and quickly implemented into a customer system.
Do you want to discuss more? Contact a KEB engineer today.
Type 38 and Intorq BFK 457/458 – how do they compare?
There are a multitude of reasons to switch from a Lenze Intorq BFK457 and BFK458 to a KEB Type 38 Brake. KEB can offer quick delivery and service with local production and stocked parts located in the central US.
KEB also offers many variations of the brake including a high torque option that uses a high energy friction lining and has a wider range of torque ratings than the Intorq BFK458. The Type 38 is able to be used in static operation with the Combistop H, and dynamic operation with possible high speeds with the Combistop N.
Similarities make changing easy
There are some similarities between the Intorq and the KEB brake product. Both brakes use a 3 point bolt pattern with similar diameters that are specified in the KEB manual. Hub lengths are comparable among similar-sized brakes and can be swapped out as one of the many variations of the KEB type 38 brake.Comparing bolt patterns of the KEB Type 38 versus the Intorq BFK series most of the bolt pattern radii are the exact same. These attributes make the switch from Intorq to KEB pretty straightforward.
Process for crossing over a brake
1) Download the KEB brake manual Download the manual for reference of dimensions and ratings. Also gather the appropriate manuals and nameplate information from the brake you plan to cross over.
2) Check the torque needed Make sure you know what torque is needed, and match the torque necessary on the manual.
KEB “Version N” brakes are intended to be used in applications where the brake is being used to dynamically stop repetitively. “Version H” brakes are used for holding applications with the capability to provide e-stops.
|Type 38 Size||Version N||Version H|
|Rated torque (Nm)||Power input (W)||Rated torque (Nm)||Power input (W)|
3) Verify the size of the hub needed Be sure to measure the size of the shaft and type of keyway in order to match the necessary hub. The customer should also verify the size of the radius of the brake they have. Note whether the dimensions are english or metric.
If the hub bore is special – like a spline – you will need to contact KEB for assistance.
4) Verify if the shaft has a key or not If the shaft has a key in it, be sure hub has a keyway cut.
5) Verify that the friction surface will suffice If the provided mounting surface does not work to produce correct friction, a suitable friction surface will need to be installed. KEB offers a secondary friction plate for this purpose, or the integrator can choose to add a KEB flange.
Click here to view the surface friction requirements
Before installing the failsafe brake KEB COMBISTOP observe the following:
1) Provide a suitable 2nd friction surface. Plane friction surfaces made out of suitable cast iron or steel. The surface roughness RZ should not exceed 25 µm. Avoid sharp-edged interruptions in the friction surface. If such a surface is not available a friction disc or flange can be used optionally.
2) The excentricity of the mounting hole circle to the shaft end shall not exceed following values: Size 02: 0,2mm; Size 03…06: 0.4mm; Size 07…10: 0.5mm.
3) The angular deviation of the mounting surface to the shaft shall not exceed following values: Size 02…03: 0.04 mm; Size 04…05: 0.05 mm; Size 06…07: 0.06 mm; Size 08…10: 0.08 mm (in reference to the bolt diameter).
4) The friction surfaces must be free from grease and oil.
5) Humidity, aggressive fumes and similar things can cause the rusting in of the friction lining. In such cases rustproof friction discs are optionally available.
6) The movement of the armature shall not be obstructed by objects substances that penetrate into the nominal air gap. If necessary,the protective rings (optionally) are to be used or other protective measures are to be taken.
6) Verify physical dimensions of the current brake Be sure that the physical dimensions of the brake selected based on the torque and shaft size fits inside the physical space provided. Be sure the bolt pattern fits with the current bolt pattern, or drill new holes for the bolts.
7) Verify the extra options desired on the brake Determine what options are wanted on the application. Available options include hand release, microswitch, dust protection ring, and a variety of flanges.
If you have any questions about crossing over your brake, feel free to contact a KEB engineer today.Speak with our engineers
KEB has a reputation for being able to run many different motor types from many different motor manufacturers. This includes induction motors, salient pole servo motors, interior pole servo motors, linear motors, and synchronous reluctance motors.
We were able to prove that again recently by helping with a retrofit opportunity that involved running a Yaskawa Sigma 5 servo motor on a Grinding machine.
This blog post will describe the steps taken to solve the application and how those could apply to other retrofit solutions.
For this retrofit application, KEB was contacted to replace a Yaskawa Sigma-5 servo amplifier. The amplifier was being used to run a Yaskawa brushless servomotor in closed loop speed control using incremental encoder feedback. The stated reason for the retrofit was because the machine tool OEM was unhappy with the lifecycle of the original VFD.
The first issue with replacing the drive was that the existing encoder was proprietary and the servomotor couldn’t be run in open loop. However, this made the application an ideal fit for KEB’s Sensorless Closed Loop (SCL) control.
SCL provides closed loop speed control, without requiring encoder feedback. The application also required EtherCAT communications, so KEB’s F6K was the perfect solution. The F6K comes standard with EtherCAT onboard, an all-in-one control firmware that includes SCL, and additional benefits such as SIL3 Safe-Torque-Off.
Once the drive was selected and received by the customer, the programming could begin. In order to start the SCL control, a motor identification by the drive is typically required. This allows the VFD to make an equivalent circuit diagram so the motor model, and thus the motor control, is more accurate.
The motor identification requires the input of basic nameplate data, which in the case of a PM motor is: rated current, rated speed, max current, rated voltage, rated torque, rated frequency, and max torque. Unfortunately for this case, not all of the required values were published, so a workaround was required. After learning the number of pole pairs in the motor, the rated frequency could be calculated, and the motor identification could be tested until successful.
Once the motor identification was complete, it was possible to begin running the motor. The next hurdle was the rotor detection. Upon each startup of a synchronous motor, the drive must determine the system offset. When there is feedback, the offset is the mechanical difference between the rotor position and the position of the installed encoder. This offset doesn’t change between runs and is stored in a drive parameter.
For SCL operation, the rotor aligns to a defined starting position before ramping up to the command speed. There are three ways to do this in KEB’s generation 6 drives: constant voltage vector (cvv-default for SCL), five-step, and high-frequency injection.
When using the default cvv, every 5-10 startups there would be a growling noise from the motor and the rotor detection would fail. During cvv, a voltage vector with constant electrical position is output to the motor. To troubleshoot the detection failures, adjustments were made to the amount of current used during alignment and the amount of time the current was built up and held. Minimal differences were noticed while changing these values, so the rotor detection was switched to five step.
The five step method uses the saturation of the motor for detection of the rotor position by applying five different voltage vectors within a few milliseconds. In this method, the possible adjustments are the current and error threshold. The current is desired to be as high as possible without causing too many overload or overcurrent errors, since a higher current causes higher saturation and thus more precise identification. The error threshold should be as low as possible, without being too low where it causes an identification failure too often.
After switching to the five step method and finding a good balance between these two values, the rotor detection errors were almost completely eliminated.
Application Specific Adjustments
After troubleshooting the rotor detection, it was possible to move onto the more standard adjustments for the application. The most important change was increasing the proportional and integral gains so the drive responded quickly to load changes. Other changes included application specific data such as torque limits and acceleration rates. Once the adjustments were complete, the customer was satisfied with the performance and the retrofit was deemed a success.
While these specific adjustments may not be necessary on every retrofit, they show how the drives from KEB America can be successfully used in all applications with the help of an Application Engineer.
If you have questions about a new or existing project that could use KEB’s expertise, contact us today.
Historically, connecting two different communication networks was handled by a dedicated network gateway. We worked on an application a couple months ago where we were able to implement this gateway functionality in an HMI LC. This is what it looked like.
The customer’s main PLC was an Allen-Bradley communicating with EtherNet/IP (protocol 1). The AB PLC connected to a machine panel that used a KEB HMI LC.
The HMI LC used EtherCAT (protocol 2) to control a 200Hp F6-K EtherCAT VFD.
EtherCAT for the VFD
EtherCAT was chosen because it provides a high-speed CAT5 connection to the drive. Also, programming the drive communication is made easy through the KEB’s EtherCAT communication handler Function Block.
A group of parameters was defined for the EtherCAT process data (PDO). The PDO gives cyclical and high-speed updates on the critical parameters.
Additionally, we implemented the DIN66019 II protocol (protocol #3) which can be used to read/write individual drive parameters. Beyond the fast-channel EtherCAT PDO parameters, this gives the ability to access every KEB drive parameter including fault codes, warnings, etc. It also provides the functionality to do a full upload and download of drive parameters.
The HMI LC can then relay any drive parameter back to the upstream PLC via EtherNet/IP. In short, the HMI LC is acting as a gateway to handle the 3 different communication protocols.
Mix-and-Match other Communication Protocols
This same concept can be extended to the other 40+ protocols supported by the HMI products. This includes Modbus, Profinet, etc. Even serial fieldbus networks Data Highway, DH+, and Profibus are possible.
So why would somebody prefer to implement this solution with the HMI LC instead of a communication gateway? It’s a fair question. The reason is that the HMI LC gives you a lot more flexibility and functionality than the traditional network gateway hardware.
It’s obvious but worth highlighting – The HMI LC adds visualization. In this application, it served as a drive remote operator, displaying speed, load, temperature, drive status and error history.
Additionally, it offers the possibility to display PDF manuals, diagnostics, logs, error history, trending information, etc. You won’t get that with a gateway-only device.
Secure Remote Access with CONNECT™
Each HMI LC ships with a Combivis CONNECT™ Runtime. This allows a secure VPN connection to be made to the machine which improves troubleshooting and diagnostic gathering.
The HMI LC offers the possibility to handle the entire machine control including EtherCAT remote I/O. From that standpoint, it becomes a very good value.
Automatic Drive Download
If a replacement drive needs to be installed at some point in the future, the HMI LC can automatically download the correct program. Again, this functionality is made easy with an included KEB Function Block in the Combivis Studio software. This functionality makes long-term support for the machine easier.
With over 40 communication drivers, the HMI LC can act as a gateway between two different networks. But the HMI LC is much more than a gateway. The HMI LC offers a lot of value and is a scalable product that increases a machinery OEM flexibility and maintainability.
If you are interested in more information on the HMI LC contact a KEB engineer today.
Email KEB America
In this post, I’ll describe the process I use for sizing gearboxes and geared motors.
To make the selection, I am using KEB’s software sizing program called KEB-DRIVE. KEB-DRIVE is free and easy to use. If interested to follow along, you can download a copy of the software.
1. Consider the application requirements
Before you begin selecting a geared motor, you first need to consider and know the application requirements. This is not a comprehensive list but gives a general idea of the common considerations.
Torque & Speed
- What torque and speed are required at the output of the gearing?
- What does the typical torque profile look like?
- Is the loading more or less steady – or will the gearing experience shock loading?
- What electrical power do I have (three phase, 50 or 60Hz, Voltage)?
- What is the duty of the application?
- If I need more motor overload – can I rate for a reduced duty like S2 or S3?
- Does the application require position, torque or speed control?
- Will the motor be run across the line or with a VFD?
- Will the motor hold the load at 0 speed indefinitely (e.g. hoisting application)?
- Does the motor need a spring-set brake on it?
- Does it need a feedback device like an encoder?
- How will the gearmotor be mounted to the machine – foot mounted, shaft mounted, flange mounted?
- Are there space constraints?
- Does the output axis need to be inline or at a right angle
- What environment is the gearmotor going into (e.g. caustic washdown, saltwater, sensitivity to noise, etc.)?
- What are the ambient temperature ranges during operation?
- Does it require special ingress protection (washdown, outdoors, etc.)?
- Is this a food processing application that will require food grade lubricants and grease?
2. Select the correct gear technology for the application
Configurations in KEB-Drive start at the top left. On the left, you’ll see drop-downs to select different gear types and sizes.
KEB offers 4 main types of gearing:
4 Types of KEB Gearing
|“Style”||Gear Type||Output||Efficiency (%)|
Helical-Worm and Helical-Bevel will provide right angle outputs. Helical-worm can be cost advantageous for larger reduction ratios. Helical-bevel has the advantage of better efficiency, which can possibly equate to a smaller motor.
There is also an option available to leave off the gearing if are just interested in selecting a servo or induction motor.
3. Motor Selection (Size, voltage, frequency)
Working to the right, I then select the size of the motor I want. Options for both Induction motors and AC Servo motors are listed. Here is a comparison of the advantages between servo and induction motors.
There is a tab that allows you to select the stator winding information – specifically, the rated voltage and frequency. KEB has the ability to offer special windings outside of what is listed. Last year I worked on a 380V/60Hz installation in South Korea – who knew!
Larger motors will provide more torque. As you increase the motor size, you’ll see the torque information is updated in torque/speed drop-down.
4. Adjust the Torque/Speed selection
Is it a speed reducer? Or a torque Increaser? It’s both – higher gear ratios will provide lower output speeds and higher torques. Use the drop down to see all the different possible configurations with the selected gearbox/motor combo.
There is a limit to the options that KEB-Drive will show. Only options with a service factor of 1.0 or greater are displayed.
Note: If you have selected a motor winding that is rated for both 50 and 60Hz, you will see two values listed for the speed and torque. The 50Hz rating will be reflected with the slower rpm output.
5. What is the gearing Service Factor and why is it important?
The gearing service factor (SF) is the ratio between the:
In other words, Service Factor provides a relative comparison to how much capacity the gears have in the current configuration.
A SF of 1.0 means the gears will have a nominal output torque equal to that of their rating. Selecting a motor/gear configuration with a SF of less than 1.0 is not advised. This means the gears will be undersized when operated at the nominal point. This could also indicate that the motor selected is too large.
Sometimes, the application is very difficult with regards to Duty, Shock loading, Temperature, etc. (look at step 1 – application requirements). In this case, it is advisable to select a very high SF which compensates for the factors that will stress, wear, and possibly damage the gearing.
Manufacturers typically provide a table of typical applications. Many also list a multiplication factor based on duty. It is advised that difficult applications like a Rock Crusher have a SF in the 3.0 range or higher. Relatively easy applications like fans with light duty might have a SF closer to 1.0. It often becomes a trade-off between safety factor and cost.
At this point, if the selection is not able to meet the required torque, speed, and SF of the application, you’ll need to return to step 2 and select a different gear and motor combination. Or conversely, if the motor or gear appear to be oversized, then you can return to step 2 in order to optimize.
6. Select gearmotor options (mounting style)
This section allows a user to select how the geared motor will be mounted. The flexibility of mounting is one reason that the KEB integral gearmotor solution has been so popular. Users can select a unit with an output shaft. Or a shaft mounted unit with a hollow bore. Mounting feet and mounting flanges can also be selected.
For shaft mount applications, a nice option is a shrink disk mounting. KEB’s shrink disc mounting provides a zero backlash connection between the gearbox and machine shaft. Assembly and disassembly are very easy.
To go along with the flexibility-theme, users can select either English or Metric units on the shaft/bores. If you don’t see the exact option you want in the configurator, then I suggest contacting a KEB engineer to explore what is possible. We are able to offer a lot of customer flange and bore designs if the customer wants.
This section also includes the lubrication used in the gearbox. A number of different lubricants are possible depending on the application requirements. Consult the KEB gearmotor manual but the temperature ranges for the lubricants is listed. For food and packaging applications, a USDA food-grade lubricant is available.
Below that is a list of checkboxes that can be selected. Gearing options like low backlash and protection covers are possible.
7. Choose the motor options
This is where a user selects the motor options. Options like a motor on the brake. Or, the type of encoder for closed loop applications. Even the type of motor fan can be selected here.
8. General options
Next, the general options can be defined. These are special requirements that can be easily selected in the configurator. This includes a second nameplate, condensation drain hole, etc, The conduit box orientation and the fitting location are also defined here.
Finally, the paint treatment can be selected here. The number of applications and thickness of paint is defined. Consult the KEB gearmotor catalog for the specifications. Added protection is possible with the P1, P2, or P3 options. These would be good options to consider for washdown, outdoor, and maritime gearmotor applications.
The paint color is also defined here. Gray and black are most commonly requested so they are standard options. But we can paint to whatever color the customer specifies. In the case of a special, contact KEB.
9. Gather 3D models and dimensional drawings
The last option is the mounting position of the gearmotor. This is important as it determines the oil fill level of the gearmotor and venting.
At this point, the user can explore additional tabs in KEB-DRIVE in order to get more information. Of note, the customer can get extra motor information including the efficiency values, nominal torque, and inertia values.
The Dimensions tab includes a drawing with critical dimensions and 3D .step models.
KEB-Drive is a useful tool because it is easy to use and selections can be made very quickly. However, please note that these are only the commonly requested features. There are many more possibilities KEB can offer like absolute or safety encoders, quiet brakes for theatre or elevator applications, custom flanges, etc.
If you have specific needs feel free to consult with a KEB gearmotor engineer and we’d be happy to help with your application.
There are a number of issues that arise when a VFD and motor are mounted far apart. A previous post went over voltage spikes due to dV/dt of the drive’s PWM switching. The answer to that problem was a dV/dt choke or sinewave filter.
For closed loop applications, another problem that can arise when a drive and motor are located far apart has to do with the encoder signals. Specifically, the voltage drop experienced on encoder signals.
This post will outline the problems of long feedback cable runs and how to address them.
Voltage Drop of Encoder Signals
The encoder cable is basically a transmission line carrying the encoder signal from the encoder device to the encoder card on the VFD. The encoder cable has some impedance which is a characteristic of the cable design.
The cable resistance should be listed on the manufacturer’s cable data sheet. The resistance is usually listed as some value per length – (e.g. Ohms/meter or Ohms/ft.). The longer the cable the more resistance it will have. And the more cable resistance, the more voltage drop the signal will have.
Let’s look at an example. Assume a worst-case scenario of a 200mA current draw. Using the data above for a 75-meter application, a TTL signal will lose 1.05V due to the voltage drop.
The most commonly used incremental encoders are the TTL type and have a target “on” voltage level of 5V. However, the drive’s encoder card will have an acceptable range on the voltage level that the drive or encoder input will accept. For example, KEB’s encoder cards recommend a minimum of 4.75V for the “High” TTL signal.
If there is too much voltage drop the TTL signals, you will get erratic operation and nuisance trips – the worst kind and a pain to troubleshoot. A common error is that the A or B channel compliment does not match the respective channel. With KEB Combivert F5 inverters, this will result in the E.EnC1 fault.
So if you are experiencing random encoder faults and suspect too much voltage drop, here are 7 things you can do to address the issue.
1. Use a Shorter cable
This one is simple but is worth mentioning because it might be the easiest to implement – if possible, use a shorter feedback cable. I’ve seen many applications where they use a “standard” cable or something they have on the shelf. The result is they use a much longer encoder cable than they really need.
An excessively long feedback cable can also couple unwanted noise and introduce other issues. So, use the shortest possible encoder cable that is practical for the application.
2. If powered from the VFD – Increase the supply voltage
Some encoders receive power from the drives control/encoder card. The Push-Pull type TTL encoders will output a signal amplitude that is proportional to its supply voltage (i.e. there is no regulated supply onboard). With these types of encoders, there are effectively two conductor voltage drops – the supply, and the return.
KEB’s F5 drive uses a fixed 5.2V supply to power the encoder. The idea is that the extra .2V compensates for some voltage drop. Some other encoder cards have means to increase the supply voltage.
If possible, you can adjust the encoder card supply voltage up. Just be sure to use a voltmeter to measure the supply voltage and check the encoder specs to make sure a higher voltage is permitted.
3. Apply power at the encoder
Another option (if supported by the encoder) is to apply the supply power directly to the encoder. Since the supply is directly applied to the encoder, this allows only one voltage drop on the feedback signals – effectively cutting the total voltage drop in half compared to the initial example.
Check your encoder datasheet to see how the encoder can be powered. Some encoders can only be powered from the drive’s encoder card. However, other encoders are designed to allow a direct power source. Some might even allow a higher input voltage like 24V but then regulate the output voltage accordingly (e.g. 5V).
So do check the encoder data sheet and see what the input power options are.
4. Consider using HTL logic
A “High” or “On” level for HTL logic is defined between 15V and 30V, with a target of 24V. KEB F5 HTL encoder cards will have a regulated 24V supply that can be used to power the encoder. Because the HTL signal is higher, it can support more of a voltage drop before hitting the lower “On” threshold.
HTL provides much more room for voltage drops – 9V from the regulated supply to the lower threshold (24V-15V = 9V). Compare that with TTL’s range of only 3V from supply to lower “High” threshold (5V-2V).
Just be sure that the drive’s encoder card supports an HTL input or the card could be damaged.
5. Use an encoder cable with lower resistance
KEB offers special encoder cables for long distance runs. The cables use larger conductors so they have less resistance. Less Ohms/meter will result in less voltage drops on the feedback signal.
6. Use a signal repeater
Another option is to use a signal repeater. Signal repeaters were commonly used before real-time fieldbuses like EtherCAT were available. They function by splitting, amplifying and conditioning the encoder signal.
KEB offers a signal repeater like this (00F4072-2008) that can be used for long run and multi-follower applications.
7. Use Fieldbus I/O – Like KEB’s Counter module
Another option is to use a fieldbus encoder module to transfer the data.
KEB’s encoder module allows the input of up to 2 TTL encoder signals. The encoder signal is wired to the module where it is converted and transferred via the EtherCAT bus.
One big advantage with this solution is the low cost of a CAT5/6 cable. The cabling cost will be much less than a long encoder cable. The second advantage is that the position is now on the bus and available for use by the control without any other handling.
One consideration with this implementation is the input delay. The listed value for the input delay on the KEB module is 1ms. This will be suitable for most motion applications but you’ll want to verify it with your individual application.
I’d be interested to hear of other solutions or problems you’ve encountered. Leave your comments below.
Have questions? – Contact a KEB Application Engineer today.