Walk into any die shop in the US and nine out of ten times, we discover diffuse reflective sensors being used to detect a large part or a small part exiting a die. Many people have success using this methodology, but lubrication-covered tumbling parts can create challenges for diffuse-reflective photoelectric sensing devices for many reasons:
Tumbling parts with many “openings” on the part itself can cause a miss-detected component.
Overly-reflective parts can false triggering of the output.
Dark segments of the exiting part can cause light absorption. Remember, a diffuse sensors sensing distance is based on reflectivity. Black or dark targets tend to absorb light and not reflect light back to the receiver.
Die lube/misting can often fog over a photoelectric lens requiring maintenance or machine down time.
The solution: Super Long Range Inductive Sensors placed under chutes
Most metal forming personnel are very familiar with smaller versions of inductive proximity sensors in tubular sizes ranging from 3mm through 30mm in diameter and with square or “block style” inductive types (flat packs, “pancake types”, etc.) but it is surprising how many people are just now discovering “Super Long Range Inductive Proximity” types. Super Long Range Inductive Proximity Sensors have been used in metal detection applications for many years including Body-In-White Automotive applications, various segments of steel processing and manufacturing, the canning industry, and conveyance.
Benefits of Using A UHMW Chute + Super Long Range Inductive Proximity Sensor in Part Exit/Part-Out Applications:
It is stronger and quieter than parts flowing over a metal chute, readily available in standard and custom widths, lengths and thicknesses to fit the needs of large and small part stampers everywhere.
UHMW is reported to be 3X stronger than carbon steel.
UHMW is resistant to die lubes.
UHMW allows Super Long Range Inductive Proximity Sensors to be placed underneath and to be “tuned” to fit the exact zone dimension required to detect any part exiting the die (fixed ranges and tunable with a potentiometer). The sensing device is also always out of harm’s way.
Provides an option for part detection in exiting applications that eliminates potential problems experienced in certain metal forming applications where photoelectric sensing solutions aren’t performing optimally.
Not every Part Exit/Part-Out application is the same and not every die, stamping application, vintage of equipment, budget for sensing programs are the same. But it’s important to remember in the world of stamping, to try as consistently as possible to think application specificity when using sensors.That is, putting the right sensing system in the right place to get the job done and to have as many technical options available as possible to solve application needs in your own “real world” metal forming operation. We believe the UHMW + Super Long Range Inductive System is such an option.
In one of my previous post we covered “How do I wire my 3-wire sensors“. This topic has had a lot of interest so I thought to myself, this would be a great opportunity to add to that subject and talk about DC 2-wire sensors. Typically in factory automation applications 2 or 3 wire sensors are implemented within the process, and as you know from my prior post a 3 wire sensor has the following 3 wires; a power wire, a ground wire and a switch wire.
A 2-wire sensor of course only has 2 wires including a power wire and ground wire with connection options of Polarized and Non-Polarized. A Polarized option requires the power wire to be connected to the positive (+) side and the ground wire to be connected to the negative side (-) of the power supply. The Non-Polarized versions can be wired just as a Polarized sensor however they also have the ability to be wired with the ground wire (-) to the positive side and the power wire (+) to the negative side of the power supply making this a more versatile option as the sensor can be wired with the wires in a non – specific location within the power supply and controls.
In the wiring diagrams below you will notice the different call outs for the Polarized vs. Non-Polarized offerings.
Note: (-) Indication of Non-Polarized wiring.
While 3-wire sensors are a more common option as they offer very low leakage current, 2 wire offerings do have their advantages per application. They can be wired in a sinking (NPN) or sourcing (PNP) configuration depending on the selected load location. Also keep in mind they only have 2 wires simplifying connection processes.
For more information on DC 2- Wire sensors click here.
When the topic of welding comes up we know that our application is going to be more challenging for sensor selection. Today’s weld cells typically found in tier 1 and tier 2 automotive plants are known to have hostile environments that the standard sensor cannot withstand and can fail regularly. There are many sensor offerings that are designed for welding including special features like Weld Field Immune Circuitry, High Temperature Weld Spatter Coatings and SteelFace Housings.
For this SENSORTECH topic I would like to review Weld Field Immune (WFI) sensors. Many welding application areas can generate strong magnetic fields. When this magnetic field is present a typical standard sensor cannot tolerate the magnetic field and is subject to intermittent behavior that can cause unnecessary downtime by providing a false signal when there is no target present. WFI sensors have special filtering properties with robust circuitry that will enable them to withstand the influence of strong magnetic fields.
WFI sensors are typically needed at the weld gun side of the welding procedure when MIG welding is performed. This location is subject to Arc Blow that can cause a strong magnetic field at the weld wire tip location. This is the hottest location in the weld cell and typically there is an Inductive Sensor located at the end of this weld tooling.
So as you can see if a WFI sensor is not selected where there is a magnetic field present it can cause multiple cycle time problems and unnecessary downtime. For more information on WFI sensors click here.
In my last post (We Don’t Make Axes Out of Bronze Anymore) we discussed the evolution of technologies which brought up the question, can a prox always replace a limit switch? Not always. Note that most proxes cannot directly switch large values of current, for example enough to start a motor, operate a large relay, or power up a high-wattage incandescent light. Being electronic devices, most standard proxes cannot handle very high temperatures, although specialized hi-temp versions are available.
A prox is designed to be a non-contact device. That is, it should be installed so that the target does not slam into or rub across the sensing face. If the application is very rough and the spacing difficult to control, a prox with more sensing range should be selected. Alternately, the prox could be “bunkered” or flush-mounted inside a heavy, protective bracket. The target can pound on the bunker continuously, but the sensor remains safely out of harm’s way.
If direct contact with a sensor absolutely cannot be avoided, ruggedized metal-faced sensors are available that are specifically designed to handle impacts on the active surface.
Be sure to consider ambient conditions of the operating environment. High temperature was mentioned earlier, but other harsh conditions such as disruptive electrical welding fields or high-pressure wash-down can be overcome by selecting proxes specially designed to survive and thrive in these environments.
Operationally, another thing to consider is the target material. Common mild carbon steel is the ideal target for an inductive prox and will yield the longest sensing ranges with standard proxes. Other metals such as aluminum, brass, copper, and stainless steel have different material properties that reduce the sensing range of a standard prox. In these cases be sure to select a Factor 1 type proximity sensor, which can sense all metals at the same range.
Every technology commonly in use today exists for a reason. Technologies have life cycles: they are invented out of necessity and are often widely used as the best available solution to a given technical problem. For example, at one time bronze was the best available metallurgy for making long-lasting tools and weapons, and it quickly replaced copper as the material of choice. But later on, bronze was itself replaced by iron, steel, and ultimately stainless steel.
When it comes to detecting the presence of an object, such as a moving component on a piece of machinery, the dominant technology used to be electro-mechanical limit switches. Mechanical & electrical wear and tear under heavy industrial use led to unsatisfactory long-term reliability. What was needed was a way to switch electrical control signal current without mechanical contact with the target – and without arcing & burning across electrical contacts.
Enter the invention of the all-electronic inductive proximity sensor. With no moving parts and solid-state transistorized switching capability, the inductive proximity sensor solved the two major drawbacks of industrial limit switches (mechanical & electrical wear) in a single, rugged device. The inductive proximity sensor – or “prox” for short – detects the presence of metallic targets by interpreting changes in the high-frequency electro-magnetic field emanating from its face or “active surface”. The metal of the target disrupts the field; the sensor responds by electronically switching its output ON (target present) or OFF (target not present). The level of switched current is typically in the 200mA DC range, which is enough to trigger a PLC input or operate a small relay.
In my next post, I will explain the do’s and don’ts for applying inductive prox sensors.
I recently had the opportunity to attend Hannover Fair in Germany and was blown away by the experience… buildings upon buildings of automation companies doing amazing things and helping us build our products faster, smarter and cheaper. One shining topic for me at the fair was the continued growth of new products being developed with IO-Link communications in them.
All in all, the growth of IO-Link products is being driven by the need of customers to know more about their facility, their process and their production. IO-Link devices are intelligent and utilize a master device to communicate their specific information over an industrial network back to the controller. To learn more about IO-Link, read my previous entry, 5 Things You Need to Know about IO-Link.
In typical sensors all you get is ON or OFF… we just hope and assume that the prox is working, until something doesn’t work properly. The part is seated but the sensor doesn’t fire or the operator can’t get their machine to cycle. This can sometimes be tricky to troubleshoot and usually causes unplanned interruptions in production while the maintenance teams attempt to replace the sensor. On some recent customer visits on the east coast, I have had a number of interesting conversations about the customer’s need to collect more information from their sensors; specifically questions like:
How do I know the sensor is working?
How do I predict sensor failure?
How do I know something has changed in the sensor application?
How do I get my sensor to provide adaptive feedback?
How do I plan preventative maintenance?
How can I increase the overall equipment throughput?
Recently Hank Hogan published an article in Control Design titled “Sensor, Diagnose Thyself.” (To be honest, I really wanted to steal his title for my blog entry.) I think Hank did a great job dissecting the key benefits of smart sensors and the amazing things you can do with them. Utilizing the technology IO-Link (that we have discussed in many past Blog Entries), sensors can communicate more with the controller and provide more data than ever before.
Some of the key points that I really thought are useful to maintenance and engineers at end-user facilities or machine builders:
Being able to detect and notify about pending failures; for example a photoeye’s lens is dirty and needs to be cleaned.
A failed sensor needs to be swapped out quickly; IO-Link allows for the smart sensors settings to be cloned and the swap to be executed super fast.
Configure a sensor before installation; program with your laptop: sample rate, response time, measurement settings, on/off switch points, anything!
One platform can be used for many sensor types; this gives familiarity to a single interface while using multiple sensor types and technologies.
In the future sensors in a wireless cloud would self-heal; this is an amazing concept and if we can figure out the price for radios and batteries to make it cost-effective, I think this could be a game changer someday.
But all that being said, it really comes down to the total cost of ownership doing it the standard sensor way versus the smart sensor way. I think you will pay more upfront in capital but down the line there will be less cost in maintenance and downtime.
It’s another day at the plant, and the “Underside Clamp Retracted” sensor on Station 29, Op 30 is acting up again. Seems to be intermittently functioning…the operator says that the line is stopping due to “Error: Underside Clamp Not Retracted”.
You think to yourself, “Didn’t we just replace that prox last week?” A quick check of the maintenance log confirms it: that prox was indeed replaced last week. In fact, that particular prox has been replaced seven times in the last six months. Hmm….the frequency of replacement looks like it’s going up…four of the seven replacements were performed in the last two months.
What’s going on here? Is it really possible that seven defective proxes just all happened to end up at Station 29, Op 30, Underside Clamp Retract? Not likely!
We often hear companies talk about how great their products are or how well they hold up under adverse conditions, but many of us wonder just how much of that is hype. While I cannot vouch for all the claims out there, I can relate to you (the reader) and share my Balluff prox story and how I’ve seen them survive.
I was working in the industrial maintenance field when I came across the prox in this tale. The prox was being used to sense motion of sanding tape in a polishing machine. This system was designed to polish the part in two directions and the purpose of the prox was to ensure that a proper amount of sandpaper had advanced with each direction change. The sandpaper was on rolls, which threaded through some rollers, including a plastic one that had a piece of metal embedded inside. The prox was set up to monitor this plastic roller and register when the metal piece rotated by and thereby indicating to the system that the sandpaper had advanced. If this prox did not change states, the system would fault out and turn on an error/alarm light. To reset the alarm the operator had to hit a reset button and then start the system again.