This is the unedited transcript for webinar: Encoder integration in 2016: New modes of installation, networking, and more. Click here to watch the presentation on demand.
In this webinar — Encoder integration in 2016: New modes of installation, networking, and more — Lisa Eitel and Steve Dilts cover the latest in rotary position encoders. We explore where mechanical, optical, magnetic, and capacitive encoders excel, and what features have been added in the last few years.
Next, we review the physical permutations available to engineers for rotary position encoders — including seal options, mounting and bearing options, housings, ratings, and modular setups that have become increasingly customizable. Then we give some examples of consumer-grade designs, industrial setups, and commercial feedback applications, and which physical permutations are most common for each.
Finally we get into control electronics and the encoder signals themselves … and compare issues and capabilities and modes of measuring in resolution, interpolation, and signal processing. We define and explain commutation channels, prevention of signal degradation, the functions of automatic gain control (AGC), signal processing, and control integration as it relates to encoders in general.
Lisa Eitel: Hello and welcome to today’s webinar — Encoder integration in 2016: New modes of installation, networking, and more … brought to you by Design World magazine and Encoder Products Company. My name is Lisa Eitel and I’m an engineer editor with DESIGN WORLD magazine. Before we begin, let me explain how you can participate in today’s presentation.
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Just a quick bit about me: Again, I’m Lisa Eitel, Senior Editor at Design World with a Bachelor of Science degree in mechanical engineering from Fenn College (now Washkewicz College) at Cleveland State. I’ve been a technical writer for 14 years. Today, I cover motors, drives, motion control, and mechanical power transmission for Design World and serve as a judge for our local FIRST Robotics competitions.
Our sponsor Encoder Products Company is a designer and manufacturer of motion sensors. Today, it’s the largest privately-held encoder manufacturer in North America, producing incremental and absolute rotary encoders … inventor of the original Cube encoder, the first Opto-ASIC maker, and the first to include flexible mounts for hollow shaft encoders. Its headquarters and manufacturing are in Idaho.
Joining us today is also Steve Dilts — from Encoder Products Company. Steve is a Business Development Manager at the Idaho headquarters. He’ll be giving us a good summary during this webinar of when to specify a magnetic encoder module. With EPC since 2006, he has held roles in technical sales, distributor relations, and marketing. Prior to joining the company, Steve was Director of Sales and Marketing for a medical and personal care products manufacturer. When not at work, he can often be found gentleman farming on his 1941 Ford tractor.
So in this webinar, we cover the latest in rotary position encoders. We explore where mechanical, optical, magnetic, and capacitive encoders excel, and what features have been added in the last few years … to satisfy such disparate applications as those in elevators to track car position and travel … to those on machine axes in CNC equipment.
Next, we will review the physical permutations for rotary position encoders — including mounting and bearing options, housings, ratings, and modular setups that have become increasingly customizable.
Then we give some examples of consumer-grade designs, industrial setups, and commercial feedback applications … and which physical permutations are most common for each.
Finally, we touch very briefly on control electronics and encoder signals … and compare issues and modes of measuring … as well as options for interpolation and signal processing.
Then we define and explain signal degradation, the basic function of automatic gain control, and control integration as it relates to encoders in general.
So, there have been a number of features added to all subtypes of rotary encoders in the last few years. No matter the subtype, just a review — rotary encoders output incremental or absolute signals to provide feedback on position and speed. Incremental signals are trains of high and low waves indicating movement but not specific position. In contrast, absolute encoders do indicate position of the rotary axis being tracked along with movement.
Mechanical encoders are actually more like rotary switches but with a digital output. They are common in consumer products for knob tracking and in medical and fitness equipment and avionics. Resolution is defined in terms of angle of throw — for a number of positions — such as 30 positions for a 360° turn, for example.
Getting into rotary encoders for real motion-control applications — capacitive encoders (mainly manufactured by CUI) use low current — an efficient option — to power a high-frequency transmitter that sends signals intermittently modulated by an etched disc before they get to a receiver. That receiver reads the capacitance variations and an ASIC translates them into angular values with resolution to forty ninety-six steps per revolution.
The most common rotary encoders today though are optical encoders. Early versions had fragile glass discs between a light source and sensing head. Increasingly common today are more rugged versions. Today, the disc can be etched metal, marked tempered glass, or engineered plastic.
Integrated electronics are also making these encoders more rugged. For example, EPC’s Opto-ASIC technology in the lower right here is a single chip combining all sensor-board components including the photosensor on one circuit. That boost resistance to particulates and electrical noise.
Another big trend is towards magnetic and magneto-strictive encoders … in part thanks to new designs based on such sensing. Common iterations of these sensors have an array of magnetic strips around a wheel. Two channels on the sensor tracks pairs of strips and output differential signal. Some designs use embedded microprocessors running signal handling software as well — to get accurate and dynamic response rivaling optical designs.
Taking the measurement tasks from opto-electric components to solid-state electronics in some cases means these encoders can be smaller and more reliable. Plus users can change the performance characteristics of these encoders more easily through software updates rather than physical changes. So, it’s easier to tailor such encoders to projects with fewer if any design compromises. This plays into a broader industrial trend to Big Data and the internet of things … as well as the trend to more preventative maintenance.
Physical permutations for rotary encoders abound. These include an array of seal, bearing, and housing options, as well as modular setups. The exploded view here is of a Heidenhain encoder with fault exclusion that detects mechanical loosening. This is actually a prerequisite for encoders that must meet Functional Safety standards, especially on machines that are getting sold internationally. You also see here a four-image series of mechanical attachment options … we recently did a video on this for BEI. You’ve got options with solid, through, and blind shafts — as well some encoders that integrate their own coupling.
Just as an aside, our sponsor EPC has a really fantastic article about picking between encoders with through or blind-bore centers. Scan the QR code here to go directly to that technical article PDF online. Another option is modular encoders — especially important for setups that just need incremental feedback. These don’t have their own bearings …but mount directly to the motor. Or check out the magnetic coupling being installed in the center picture with the fingers. A five or three eighths inch diameter shaft fits into a thru-bore encoder, and the opposite magnetic end holds to the machine shaft. This is great for temporary or even permanent but un-machinable axes.
So now consider some examples of consumer-grade designs and industrial setups … and which physical permutations excel in each. As we know, motor feedback is the most common use for rotary encoders. Here the encoder mounts to the motor shaft or tracks RPM through mechanical linkages. In the picture strip, we see an example from Duff Norton — with EPC encoders to track the position of gearmotor-driven screw jacks to lift railcars. That lets a controller synchronize multiple jacks and lift 80-ton railcars without tilting.
The middle example is a rotary encoder that withstands severe conditions with an IP67 housing.
The one on the right there is a customized through-bore encoder for an axis on a machine to orient bottles before label application. Below that from left to right we go from a stepper-motor encoder for consumer-grade robotics … to an inexpensive optical incremental encoder for large-volume OEM design. Here note that some industries’ shift from optical to magnetic encoders has meant shrinking encoder sizes … to let encoders pair with all types of motors. Medical devices in particular benefit from these increasingly compact offerings.
In the lower right you see the other extreme — a full industrial magnetic encoder that splits for fitting on large rotating axes in oil and gas, construction, and wind and marine designs.
In between these, check out all the axes needing feedback in web tensioning. Here, encoders go not on motors but tensioning arm rollers to let a master controller maintain steady web tension. Cut-to-length jobs, registration-mark timing, and backstop gauging — as well as conveying —are other encoder applications. For the latter, encoders attach to the motor or intermediate shafts. Here, encoders are particularly important where a plant line depends on coordination of multiple conveyors.
One last note — reconsider the picture in the lower left from Eva Robotics. This is one newer application — on axes running off stepper motors. In traditional setups, engineers just included a stepper motor larger than the torque demand to prevent stalling. But with the need to make machines smaller and cheaper, that’s no good anymore. So now a lot of stepper motors come with encoder feedback. Notice the mode of coupling integration here as well.
So what about direct replacements? Some manufacturers such as Fraba Posital are trying to get into this game, with cloud configuration for endusers. Essentially, users modify encoder parameters by updating device software with a handheld tool, then upload configuration data to an online database. If a replacement is needed, the manufacturer has those records on hand to supply a drop-in-ready version of the encoder.
What you see on this slide is an array of encoders from Encoder Products Company. These are all offerings based on cross referencing and retrofitting thousands of domestic and foreign encoders. Many times they’re less expensive than buying from OEMs.
Both of these examples illustrate how the concept of order-of-one manufacturing is changing even motion-component supply models.
Now let’s talk about control electronics and encoder signals themselves. The controller accepting encoder feedback will dictate what signal types are acceptable. Incremental encoders produce single-channel, dual-channel or quadra-ture output, and index-plus-quadra-ture output. As we’ll cover, some such encoders have more channels for motor commutation to replace less-accurate Hall Effect sensors when pairing with dc motors.
In addition, control schemes such as interpolation can boost overall encoder-system resolution. Just consider an optical encoder with quadrature output. Here, an interpolation circuit divides the sine-wave outputs from the optics into multiple interim positions as square waves. This can boost resolution twentyfold.
Note that encoders in designs driven by permanent-magnet motors were once used almost exclusively as position and velocity feedback. But now, commutating encoders are common too. Typical setups have the outputs for quadrature signals, plus an index — as well as three commutation-phase channel outputs. Whether six-step driven as in the center illustration or sinusoidally driven, encoders here keep each phase-current input coordinated with the motor’s corresponding back-emf-to-torque function … eliminating position and the error associated with inevitable phasing inaccuracy in the process.
One other thing here: Check out the integrated motor in the lower right-hand corner of this slide. This is a Dunkermotoren brushless dc motor. It’s representative of a larger trend towards integrated motors, as it has integrated control electronics and (thanks to power-stage electronics) makes an external power supply unnecessary. It also contains one of any number of encoders pre-engineered to be compatible with the motor’s controls and physical geometry.
So what other issues must engineers using encoders address? What are typical capabilities and modes of measuring in resolution and signal processing? After all, designs are changing across practically every market, requiring higher resolution and accuracy — even smaller encoders … especially in medical, textile and light industrial automation. Remember with rotary encoders being measuring devices, resolution is the core parameter. It’s units of angle — such as degrees or radians — some number of counts per revolution — pulses per revolution or PPR — or as a binary number of measuring steps per revolution such as a 16-bit encoder having 2 to the 16 counts per revolution. In contrast, the magnetic codewheel on this slide — it’s marked AS5311 — is from a 12-bit austria microsystems encoder which output 4,096 pulses on quadra-ture output but only for speeds to 650 mm/sec. The EPC replacement for a Siemens encoder in the upper left here can be ordered with either 1024 or 2048 CPR. Just a reminder here that CPR is Cycles Per Revolution, which is actually an expression of resolution and not accuracy.
The functional-block diagram you see with plots of error is from an article that Design World did a few years back on the importance of encoder resolution and well-designed interpolation algorithms. Note that any errors in the interpolation show at slow and fast speeds as illustrated. The article details one highly dynamic servo application — that of precision machining — in case you want to find that article at designworldonline.com. Essentially, drivetrain compliance as well as encoder position error and interpolation error can all cause wave-like markings on workpiece surfaces in such applications.
We’ll cover physical prevention of signal degradation when using encoders on the next slide. In many designs, the functions of automatic gain control or AGC as well as signal processing, and control integration are essential. During encoder-signal processing, filters analyze each cycle and remove noise — rejecting any invalid signal states. Then the controls reconstruct encoder signals in their correct sequence and form.
AGC is a closed-loop feedback circuit that uses average or peak output to dynamically adjust gain — and maintain output amplitude despite any measuring variations.
Noise immunity. How to get it? The very electric motor upon which encoders often install — not to mention the associated drives, ac power, and nearby relays and lighting can degrade the electrical signals from encoders. The issue presents with symptoms ranging from simple missteps to total servo failure.
Engineers can prevent this issue by mitigating the effect of all radiated noise — that which propagates through the air. Perhaps more importantly, one can also mitigate the effect of conducted noise traveling through encoder cables from ground loops, power supplies or other connected equipment. First off, route power and signal lines separately. Specify twisted and shielded signal cables, and put them at least a foot away from all other lines.
The QR code on this slide goes to a great piece from 2014 we did — called the problems drives cause and cable types that help solve them. One take-home point from the author there …. and others — use differential outputs with twisted and shielded cable. Complimentary signals reduce common-mode noise and distortion.
Another best practice to keep encoder signals safe — keep cable continuity from encoder to controller and minimize splices and junctions wherever possible. Also ensure all motors and drives are properly grounded.
Speaking of encoder output — after picking channel count for an encoder, engineers must pick the electrical output type. Again, an unprompted plug here — our sponsor has an awesome library of white papers in PDF form on this topic at encoders.com … so check it out. One of these papers outlines how encoder-output options include open collector or N-P-N, pull-up, push-pull or P-P (or even HTL) — and differential line driver output. As we alluded earlier, differential excels because it has two connections per channel so lets the receiving controller sift out noise. Today most incremental encoders with push-pull (HTL) or RS422 (TTL) output drivers have replaced most N-P-N (as well as P-N-P) and voltage output.
One caveat: It’s true that for more complex motion control applications — such as complex plant installations —Industrial Ethernet offers valuable advantages. One of these is the ability to network with enterprise-level functions. But smaller standalone machines can still use fieldbus or point-to-point wiring such as SSI, bit-parallel, or even analog signals.
In contrast with incremental encoders having traditional connections, fieldbus networks excel in factory automation for which they were originally made … including sub-machinery such as conveyors, mobile equipment, medical equipment, and solar panels. The bus topology of these networks simplifies wiring and supports diagnostics.
In fact, note that the number of encoders in all industries is increasing, as machines must be more flexible and reliable than ever. So here, preventative maintenance features on encoders can include warnings and error outputs. Case in point: Leine and Linde has an Advanced Diagnostic System (or ADS). The new ADS Online is the company’s diagnostic tool to support condition-based maintenance. It essentially analyzes rotary encoder condition and warns of impending faults … which is especially useful in large complex machinery.
In the new era of Industry 4.0, feedback like this —including additional information — is highly useful. No wonder then that preventative maintenance and IoT trends are spurring more networking, especially those based on Ethernet. Many note a steady trend toward the use of various forms of industrial Ethernet — including Ethernet/IP and EtherCAT — in large-scale industrial automation. This provides more scope for embedded and distributed intelligence (including condition monitoring) in devices on the factory floor. With so much data available, encoder manufacturers are adding more features to put this information to good use.
Now I turn things over to Steve Dilts from Encoder Products Company. Again, Steve is a Business Development Manager there. He’ll now be giving us a summary of when to specify a magnetic encoder module. Steve, the floor is yours.
Steve Dilts: Thank you, Lisa. I appreciate very thorough overview of a lot of the options and choices presented to companies that need to specify and purchase encoders. They were, of course, ever grateful to have the opportunity to share some information today with your audience via this webinar. We’ll take a look at one particular encoder specification choice just real quickly.
Before I do that and get into that, just playing off of what you just mentioned in regards to increasing automation. One of our local publications today [wrote 00:26:35] this article this morning was highlighting the timber industry here in Northern Idaho. It pointed out that even though we have probably one quarter of the the timber processing mills we used to have 20 years ago, fewer number of people are working in a few in number of mills and we’re actually processing and producing more product today than we did 20, 25 years ago. All of that is made possible through increased use and application of automation.
As you pointed out, a lot of that automation requires sensors. In many cases, the sensor of choice is an encoder and more specific and relevant to our discussion today, rotary encoders. As you’ve presented here, there’s a lot of choices, a lot of different, in terms of mechanical, electrical, signal processing, output types and all these things. We’ll zoom in on just a couple of those choices here and address the question: when should you specify a magnetic encoder module?
Before we answer that question, of course, we just want to define our terms. Really what we’re looking at are a couple of mechanical and electrical features. On your left in this illustration, you see what we are going to refer to as a bearing encoder. There were millions of these in place and operating. There’ll be millions more in the future. They’re very solid and stable platform for producing that rotary feedback.
At the bottom of that image, you see the housing. This housing assembly has bearings that carry the shaft. On the shaft, of course, this is the optical rotary encoder, incremental encoder, we’ve got a code disk, a light source, and the photo detector that receives that light signal and produces output current and it’s all translated into a digital output in the form of a square wave.
As all these parts and pieces components need to be properly assembled and lined, again, it’s a great product, a great baseline model to, a format for providing rotary feedback. On the right is what we’re referring to as a modular or module style encoder and all of those mechanical features in terms of the bearings are eliminated with this design. We have all the electronics in the modular housing.
This particular unit is a magnetic module versus an optical encoder, bearing encoder. Just to real quickly overviewing the technology involved here as I’ve mentioned, the optical encoder is going to have a disk with increments either printed or etched in the mylar or glass surface. Sometimes we even have the mechanical metal discs that have slots cut in them but most what we see on the market today is either glass or a film or plastic type of disc. The [mask 00:30:18] in the center of the circuit board electronics [very 00:30:22] proven technology, been around a long time and it has a great history of providing the excellent feedback.
To the right, we have a simple illustration of a magnetic sensor that has a single pole [pair 00:30:41] there with a magnet that rotates in proximity to a hall-effect sensor. As you can see, the component count is greatly reduced, simplified by looking at a magnetic solution. That has the implications for not only costs but also some factors that pertained to reliability and operability in certain harsh conditions which we’ll speak to here in just a moment.
What we’re looking at is why would you choose a modular system versus a bearing encoder? Why would you choose a magnetic sensing solution versus an optical? What are some factors that play into helping you make that choice?
One of the things we want to ask is we’re talking about do you need bearings or not in your encoder assembly. The question is: are there factors in your application that can impact the operating life of those bearings and the disk in the encoder.
You don’t have to be an encoder expert to look at these photos and say something went horribly wrong in this application. To the left there, we have an hub shaft to permanent encoder where bearing seized and had some adverse impact inside the encoder. On the right, this is example of a disk crash where the bearings failed, the encoder shaft moved beyond its limits. This glass disc was broken and that leaves you with a nonfunctional encoder.
Are there situations where you want to avoid using bearings if possible? These are some factors to think about and evaluate making that … choice. Do you have excessive radial and axial loads? This is a 5 to 40 pounds, is kind of a typical range we see with a lot of incremental encoders particularly shaft encoders. A way around that is we extend the range of those bearing loads and so we have encoders that we manufacture to go up to 80, 90, even a 100 pounds of load-bearing capability on the bearings.
When you start looking at those types of loads, now you’re ending up with a very large encoder and so you have to ask another follow-up question that you have room for all that mass. Bearing loads, are you in a situation where the loads on the encoder … or sort of the upper limit of the range of that encoder? Are there extreme shock and vibration factors? What we see here, I just put kind of a typical shot range you’ll see on an encoder, temperatures going beyond the minus 20 to minus 80. A lot of encoders, we can expand that range.
Really, in terms of bearings, it’s really what do those temperatures do to the lubricant inside those bearings and if either low or or high temperature is on the extreme end … can lead to premature bearing wear and failure. Worst-case scenario, you’ve got encoder on a piece of equipment out in some Ice Station Zebra location in the cold north and it’s sitting there for months at a time and not moving. Then somebody flips the switch and it’s got a spool up to 3,600 RPMs in a heartbeat and what’s going to happen to those bearings if the lubricant is not appropriate to that temperature situation. Extreme example there but it illustrates the point.
Also, contaminants that may get beyond the seal and work their way into bearings, of course, can cause premature failure of bearings. We see that sometimes with fine grits and particles that, in and of themselves, that seal may keep that out but overtime if there’s any moisture that accumulates, so there’s particles get into the seal shaft interface, we can see them work inside and work into the bearings overtime. Again, these are some factors that might make you want to consider a solution that does not require bearings, a high-speed application above.
Most bearing encoders rated between 6 and 10,000 RPMs, we see some that go up to 12,000 RPMs. You get much beyond that. You’re really going fast for love of the [bearings as they’re 00:35:51] typically applied in rotary encoders. In many times, the the speed limitation of the encoder is defined by the the bearing rating. Again, if we can eliminate that factor, you can go up to a higher rate of maybe 20,000 RPMs, that’s which your application requires. There are some solutions that we’ll look at the minute that you would work well in those types of applications, high-speed applications.
Then, again, certainly not the most critical factor but an important and increasingly important factor, and that is cost. Just intuitively, you can look at these two products and guess that one is going to be more costly and than the other just in terms of the components that go into the manufacture of that encoder with the housing, the bearings, the shaft and all those things, versus the the module style on the left. Again, these module type encoder is usually priced out a little point than a full industrial bearing encoder. That’s a consideration to factor into place.
In addition, are there space constraints that would lean towards a more compact solution? Lisa, you alluded to earlier to a drive towards a smaller encoders. That’s certainly something that we see as a manufacturer as well, just by the virtue of the increasing usage of sensors and rotary sensors and different applications. Medical is one that you mentioned, just more compact footprint being required by removing the bulk of the bearings and housing so you can have a much more compact solution.
A lot of times, like it or not, we find that the encoder is sort of the afterthought for the design engineer. They’ve focused on many other power train components. They come back to the [ends and say 00:37:53], “Oh, yeah. They need an encoder.” Oftentimes you might find that there’s not a lot of room left over. Anyways, module type encoders, do you offer some space saving advantages as illustrated in this image here?
Are there contaminants present that not only affect the bearings but can also affect the ability of the optical sensor to function properly? To the left, you see ingress of some [particulates and 00:38:27] solution that will present a challenge to any encoder but in particular for optical solution. We might have a hard time getting a signal or be produced from all the light passing through those accumulations of debris in that encoder.
On the right, this is example of high pressure washdown, IP ratings up to IP69K, handle a high pressure steam type cleaning. The example in this photo was of a 1,500 psi extended washdown test on a module type encoder that we manufacture. It is an example of some of the extremes that you can see in this certain application. Contaminants, solids, liquids, pressurized, all of those can lead you to a conclusion of maybe one that looked towards a module encoder type solution.
Another question: is there a risk of sensor, a disk crash because of the sensor to disk air gap. I mentioned this, this is really related to shock and vibration again and also to the wearing of bearings on the carrier shaft or perhaps on the encoder or even on the motor or some other device that the encoder rides on.
That critical gap between the disk and the sensor is what we’re talking about here. A lot of optical encoders, it could be [as ten 00:40:04] that says 2 to 4/1000 of an inch. If you have some shock that causes that disk or shaft to deflect while the encoder is turning, the disk contacts the sensor and now you have a nonfunctional encoder. Those specs are not often published or made public by encoder manufacturers but it’s something that, if pressed, the manufacturer might be able to address and share with you.
Really, the question would be to go back and look at the shock and load factors on the shaft that you’re going to be monitoring and its potential. It’s on the high end of the the shock and vibration specs and uses an optical encoder. You could have some scenarios where you might be put at risk by that, again a point to ponder in the specification process.
Some magnetic solutions are very tolerant of a wide air gap between the sensor and the rotating the shaft and also alignment of this sensor with the shaft as something to consider as well. Again, magnetic [and 00:41:22] contacting solutions like we’re going to present here in a moment and we’re showing on this slide of our way to overcome that gap in this alignment concern.
Just comparing our two solutions, the optical bearing encoder generally can provide a very high accuracy, high resolution. We have encoders that produce up to 30,000 or more cycles per revolution and with quadrature counting, that’s up to 120,000 pulses per revolution. We have encoders that are into the fractions of arcminutes in terms of accuracy. They’re tolerant of strong magnetic fields. Again, there are plenty of those out in the field and they certainly have a place.
Magnetic modules, tolerant of contaminants, tolerant of high shock and vibration that, again, by virtue of the magnetic sensing, any dust and debris that gets between the sensor and magnet will not have the same adverse impact as you might have with an LED and the photosensor and the optical encoder. They can be tolerant of high shock and vibration, compact, suitable for high-speed applications and lower-cost. Those are some factors to weigh, just in summary, when looking at optical bearing style encoder versus a magnetic module.
An example of that is our model 30M, recently released to the market. This is a 30 millimeter diameter module with all the electronics and the sensor and that injection molded housing, the whole fix sensor with an end-of-shaft magnet has up to 1024 cycles per revolution resolution and an optional IP69 case seal for washdown [duty 00:43:30] application as illustrated in some of the photos earlier. That is with the M12 connector option.
In here, we have a couple, the different connector options. Here’s an example of installation on a Bodine gear motor. Again, great for that type of Servo stepper motor feedback, some typical applications for these types of encoders, Servos, stepper motor, feedback, as mentioned, mobile equipment steering, speed sensing, timber processing equipment, studio lighting, stage equipment, things like a rotary valve positioning, monitoring, and control; solar panels for non-industrial applications.
We’ve seen things like vending machines, robotics, another application where we might apply an encoder like this, and so a wide range of possibilities there presented by the electrical-mechanical features that you find in one of these module style encoders.
Again, thank you, Lisa. We appreciate your help and that of the team at Design World. With that, I’ll turn it back over to the Design World team.
Lisa Eitel: Thank you. Thank you very much, Steve. That was fantastic. We have some questions on hand. Let’s jump into a little bit of Q and A here. First question, and some of these might be better for follow-up but I’ll just present it to you …
How does someone pick between mylar and the metal or other materials for the wheel — for the optical encoders?
Steve Dilts: Thank you, Lisa. That’s a good question. Probably the most important two factors, I guess, and they’re environmental factors. One would be the level of shock load that we talked about earlier and vibration that would lean away from a glass disk solution. On the other hand, if you’re operating in a high-temperature environment, say, at 100 degrees C, you would steer away from a plastic or mylar type disk just because it would be susceptible to deformation when exposed to those higher temperatures.
Lisa Eitel: Excellent. Next question …
What’s considered high accuracy? I know there are some qualitative references, some quantitative, for general application and precision implication.
Steve Dilts: Yeah. That’s one of those questions like what’s a standard encoder. It’s hard to say in a general sense. For most motor feedback, we see 1024, 2048 CPR, the cut-off point for a lot of vector duty motor type applications, Servo motors, course can go up to 4096.
We’ve seen rotary encoders that go up to, like I mentioned earlier, we have … over 30,000 cycles per revolution. Some manufacturers go as high as 65,000. That’s resolution which is not the same as accuracy; accuracy being how closely does the encoder signal had any given reference point on the rotation match with the ideal pulse and so accuracy and resolution really two different questions. I guess resolution is to how fine or you’re hoping to control the motion and with accuracy, it’s repeatability from one step to the next.
It’s really a question what the specific needs are with an application is where we always start when we try to answer that question for our customer.
Lisa Eitel: Excellent. Got it. Next …
Are there any rules of thumb about where it’s best you install encoder from a physical installation standpoint?
Steve Dilts: Yeah. We’re talking about rotary encoders and rotary feedback. Our recommendation is if you’re monitoring a shaft, you want to know the speed and direction of that shaft then attach your encoder directly to that shaft, the three bore or maybe a coupling. Sometimes just the physical constraints of the application don’t allow for that. We would say you have this few mechanical linkages between the encoder and the shaft or the device that you’re trying to monitor.
Another type of feedback where rotary encoders are used are with the linear displacement and linear measurement. With the rotary encoder, many times we put a measuring wheel on a shaft encoder and we might measure something like a conveyor belt as it’s turning. In this case, since what we’re really looking to measure is the travel of the actual belt itself, we would recommend let’s put a wheel on the belt surface that you want to measure and monitor and use that method. I guess the rule of thumb would be as close as and directly connected to the motion that you’re trying to measure is how we direct. This is like what we recommend to customers.
Lisa Eitel: Excellent. It looks like we’ve run out of time. This concludes our webinar. Attendees, if you happen to think of more questions, please send them our way. Another thanks to Encoder Products Company for being our sponsor. Also, thank you, Steve, for doing that deep dive there. Attendees, please note that the on demand version of this webinar will be available online and I’m going to make sure that this is showing at this URL that you see there. Thank you very much for your time …
Steve Dilts: Thank you, Lisa. It was great to be part of the program today.