Back to the Basics – Object Detection

In the last post about the Basics of Automation, we discussed how humans act as a paradigm for automation. Now, let’s take a closer look at how objects can be detected, collected and positioned with the help of sensors.

Sensors can detect various materials such as metals, non-metals, solids and liquids, all completely without contact. You can use magnetic fields, light and sound to do this. The type of material you are trying to detect will determine the type of sensor technology that you will use.

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Types of Sensors

  • Inductive sensors for detecting any metallic object at close range
  • Capacitive sensors for detecting the presence of level of almost any material and liquid at close range
  • Photoelectric sensors such as diffuse, retro-reflective or through-beam detect virtually any object over greater distances
  • Ultrasonic sensors for detecting virtually any object over greater distances

Different Sensors for Different Applications

The different types of sensors used will depend on the type of application. For example, you will use different sensors for metal detection, non-metal detection, magnet detection, and level detection.

Detecting Metals

If a workpiece or similar metallic objects Object Detection 2should be detected, then an inductive sensor is the best solution. Inductive sensors easily detect workpiece carriers at close range. If a workpiece is missing it will be reliably detected. Photoelectric sensors detect small objects, for example, steel springs as they are brought in for processing. Thus ensures a correct installation and assists in process continuity. These sensors also stand out with their long ranges.

Detecting Non-Metals

If you are trying to detect non-metal objects, for example, the height of paper stacks, Object Detection 3then capacitive sensors are the right choice. They will ensure that the printing process runs smoothly and they prevent transport backups. If you are checking the presence of photovoltaic cells or similar objects as they are brought in for processing, then photoelectic sensors would be the correct choice for the application.

Detecting Magnets

Object Detection 4

To make sure that blister packs are exactly positioned in boxes or that improperly packaged matches are sorted out, a magnetic field sensor is needed which is integrated into the slot. It detects the opening condition of a gripper, or the position of a pneumatic ejector.

 

Level Detection

What if you need to detect the level of granulate in containers? Then the solution is to use capacitive sensors. To accomplish this, two sensors are attached in the containers, offset from each other. A signal is generated when the minimum or maximum level is exceeded. This prevents over-filling or the level falling below a set amount. However, if you would like to detect the precise fill height of a tank without contact, then the solution would be to use an ultrasonic sensor.

Stay tuned for future posts that will cover the essentials of automation. To learn more about the Basics of Automation in the meantime, visit www.balluff.com.

Solve Difficult Sensing Applications with Ultrasonic Technology

When reviewing or approaching an application, we all know that the correct sensor technology plays a key role in reliable detection of production parts or even machine positioning. In many cases, application engineers choose photoelectric sensors Image1as their go-to solution, as they seem more common and familiar. Photoelectric sensors are solid performers in a variety of applications, but they can run into limitations under certain conditions. In these circumstances, considering an ultrasonic sensor could provide a solid solution.

An ultrasonic sensor operates by emitting ultra-high-frequency sound waves. The sensor monitors the distance to the target by measuring the elapsed time between the emitted and returned sound waves.

Ultrasonic sensors are not affected by color, like photoelectric sensors sometimes are. Therefore, if the target is black in color or transparent, the ultrasonic sensor can still provide a reliable detection output where the photoelectric sensor may not. I was recently approached with an application where a Image2customer needed to detect a few features on a metal angle iron. The customer was using a laser photoelectric sensor with analog feedback measurement, however the results were not consistent or repeatable as the laser would simply pick up every imperfection that was present on the angle iron. This is where the ultrasonic sensors came in, providing a larger detection range that was unaffected by surface characteristics of the irregular target. This provided a much more stable output signal, allowing the customer to reliably detect and error-proof the angle iron application. With the customer switching to ultrasonic sensors in this particular application, they now have better quality control and reduced downtime.
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So when approaching any application, keep in mind that there is a variety of sensor technologies available, and some will provide better results than others in a given situation. Ultrasonic sensors are indeed an excellent choice when applied correctly. They can measure fill level, stack height, web sag, or simply monitor the presence of a target or object. They can also perform reliably in foggy or dusty areas where optical-based technologies sometimes fall short.

For more information on ultrasonic and photoelectric sensors visit www.balluff.com.

The Latest Trend in the Stamping and Die Industry

compact-sensor-blogOne trend we see today in many applications is the need for smaller low profile proximity sensors. Machines are getting much smaller and the need for error proofing has ultimately become a must for such applications in the Stamping and Die industry. Stamping Die processes can be a very harsh environment with excessive change overs to high speed part feed outs when running production. In many cases these applications need a sensor that can provide 5mm of sensing range however they simply do not have the room for an M18 sensor that is 45 to 50mm long. This is where the “FlatPack” low profile sensor can be a great choice due to their low profile dimensions.

Proximity sensors have proven time and time again to reduce machine crashes, part accuracy and proper part location. Sensors can be placed in multiple locations within the application to properly error proof “In Order Parts” (IO) for example detecting whether a punched hole is present or not present to ensure a production part is good. All of this adds up to reduced machine downtime and lower scrap rates that simply help a plant run more efficiently.

So when selecting proximity sensors and mating cables it is very important to select a sensor that A) mechanically fits the application and B) offers enough sensing range detection to reliably see the target without physical damage to the sensor. Remember, these sensors are proximity sensors not positive machine stops. Cables are also key to applications, it is important to pick a the proper cable needed for example an abrasion resistant cable may be needed due to excessive metal debris or a TPE cable for high flex areas.

Below both sensors have 5mm of sensing range:

M18vsFlatpack

Below both sensors have 2mm of sensing range:

M8vsFlatpack

You can see that in certain process areas “FlatPack” low profile sensors can provide benefits for applications that have space constraints.

For more information on proximity sensors click here.

Miniature Capacitive Sensors for Small Part Detection

As discussed in a previous blog post, miniature sensors are an ongoing trend in the market as manufacturing and equipment requirements continue to demand smaller sensor size due to either space limitations and/or weight considerations. However, size and weight aren’t the only factors. The need for more precise sensing — higher accuracy, repeatability, and smaller part detection — is another demanding requirement and, often times, the actual main focus point.

This post will look specifically at capacitive sensors and how smaller capacitive sensors can lead to better detection of smaller parts.

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Principle of a capacitive sensor
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Parallel-plate capacitor equation

Capacitive sensors provide non-contact detection of all types of objects, ranging from insulators to conductors and even liquids. A capacitive sensor uses the principle of capacitance to detect objects. The equation for capacitance takes into account the surface area (A) of either electrode, the distance (d) between the electrodes, and the dielectric constant (εr) of the material between the electrodes. In simple terms: a capacitive sensor detects the change in capacitance when an object enters its electrical field. Internal circuitry determines if the gain in capacitance is above the set threshold. Once the threshold is met the sensor’s output is switched.

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Actuation of a capacitive sensor

When looking at small part detection, the size of the capacitive sensor’s active sensing surface plays a significant part. Now there isn’t a defined formula for calculating smallest detectable object for a capacitive sensor because of the numerous variables that need to be considered (as seen in the equation above). However, the general rule for optimal sensing is that the target size should be at least equal to the size of the sensor’s active surface. The reason behind this is if the target size is smaller than the sensor’s active surface, the electric field would travel around the target and cause unreliable readings.

Taking the general rule into consideration and comparing a miniature 4mm diameter capacitive sensor to a standard 18mm diameter capacitive sensor, it’s simple to determine that the 4mm diameter capacitive sensor can reliably detect a much smaller target (4mm) than the 18mm diameter capacitive sensor (18mm).

So when looking at small part detection, the smaller the sensor’s active sensing surface is, the better its ability for small part detection. Therefore, if an application requires detection of a small part, it’s best to start with miniature capacitive sensor.

For more information on miniature capacitive sensors click here.

The Often Overlooked Proximity Sensor

If someone says proximity sensor, what is the first thing that comes to mind?  My guess is inductive and justly so because they are the most used sensor in automation today.  There are other sensing technologies that use the term proximity in describing the sensing mode.  These include diffuse or proximity photo electric sensors that use the reflectivity of the object to change states and proximity mode of ultrasonic sensors that use high frequency sound waves to detect objects.  All of these sensors detect objects that are in close proximity of the sensor without making physical contact.

One of the most overlooked or forgotten proximity sensors on the market today is the capacitive sensor.  Why?  Perhaps it is because they have a bad reputation from when they were released years ago as they were more susceptible to noise than most sensors.  I recently heard someone say that they don’t discuss capacitive sensors with their customers because they had this bad experience almost 10 years ago, however, with the advancements of technology this is no longer the case.

CapacitiveFlushCapacitive sensors are versatile in solving numerous applications.  These sensors can be used to detect objects such as glass, wood, and paper, plastic, ceramic, the list goes on and on.  The capacitive sensors used to detect objects are easily identified by the flush mounting or shielded face of the sensor.  Shielding causes the electrostatic field to be short conical shaped much like the shielded version of the inductive proximity sensor.

Capacitive Non-FlushJust as there are non-flush or unshielded inductive sensors there are non-flush capacitive sensors, and the mounting and housing looks the same.  The non-flush capacitive sensors have a large spherical field which allows them to be used in level detection.  Since capacitive sensors can detect virtually anything, they can detect levels of liquids including water, oil, glue and so forth and the can detect levels of solids like plastic granules, soap powder, sand and just about anything else.  Levels can be detected either directly, the sensor touches the medium or indirectly where the sensor senses the medium through a non-metallic container wall.

SmartLevelWith improvements in capacitive technology sensors have been designed that can compensate for foaming, material build-up and filming of water based highly conductive liquids.  Since these capacitive sensors are based on the conductivity of liquids they can reliably actuate when sensing aggressive acids such as hydrochloric, sulfuric and hydrofluoric acids.  In addition, these sensors can detect liquids through glass or plastic walls up to 10mm thick are not affected by moisture and require little or no cleaning these applications.

The sensing distance of a capacitive sensor is determined by several factors including the sensing face area, the larger the better.  The next factor is the material property of the object or dielectric strength, the higher the dielectric constant the greater the sensing distance.  Lastly the size of the target affects the sensing range.  Just like an inductive sensor you want the target to be equal to or larger than the sensor.

Most capacitive sensors have a potentiometer to allow adjustment of the sensitivity of the sensor to reliably detect the target.  The maximum sensing distance of a capacitive sensor is based on a metal target thus there is a reduction factor for non-metal targets.

Although capacitive sensors can detect metal inductive sensors should be used for these applications.  Capacitive sensors are ideal for detecting non-metallic objects at close ranges, usually less than 30mm and for detecting hidden or inaccessible materials or features.

Just remember, there is one more proximity sensor…the capacitive one!

To learn more about Balluff capacitive sensors visit www.balluff.us.

A Sound Solution for Object Detection and Measurement

Ultrasonic sensors can detect objects that many traditional sensing technologies cannot because of their ability to see targets regardless of color, transparency and surface texture. Even in dusty, humid, or hazy environments, they may be the only sensor that is able to provide the desired results. Ultrasonic sensors are often used in liquid level measurement applications and detecting clear films.

Ultrasonic sensors emit a burst of short, high frequency sound waves that propagates in a cone shape towards the target. When the sound waves strike the target, they are bounced back to the sensor. The sensor then calculates the distance based on the time span from when the sound was emitted until the sound was received.

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