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.

Object Detection 1

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.

Smart IO-Link Sensors for Smart Factories

Digitizing the production world in the age of Industry 4.0 increases the need for information between the various levels of the automation pyramid from the sensor/actuator level up to the enterprise management level. Sensors are the eyes and ears of automation technology, without which there would be no data for such a cross-level flow of information. They are at the scene of the action in the system and provide valuable information as the basis for implementing modern production processes. This in turn allows smart maintenance or repair concepts to be realized, preventing production scrap and increasing system uptime.

This digitizing begins with the sensor itself. Digitizing requires intelligent sensors to enrich equipment models with real data and to gain clarity over equipment and production status. For this, the “eyes and ears” of automation provide additional information beyond their primary function. In addition to data for service life, load level and damage detection environmental information such as temperature, contamination or quality of the alignment with the target object is required.

One Sensor – Multiple Functions

This photoelectric sensor offers these benefits. Along with the switching signal, it also uses IO-Link to provide valuable information about the sensor status or the current ambient conditions. This versatile sensor uses red light and lets you choose from among four sensor modes: background suppression, energetic diffuse, retroreflective or through-beam sensor. These four sensing principles are the most common in use all over the world in photoelectric sensors and have proven themselves in countless industrial applications. In production this gives you additional flexibility, since the sensor principles can be changed at any time, even on-the-fly. Very different objects can always be reliably detected in changing operating conditions. Inventory is also simplified. Instead of four different devices, only one needs to be stocked. Sensor replacement is easy and uncomplicated, since the parameter sets can be updated and loaded via IO-Link at any time. Intelligent sensors are ideal for use with IO-Link and uses data retention to eliminate cumbersome manual setting. All the sensor functions can be configured over IO-Link, so that a remote teach-in can be initiated by the controller.

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Diagnostics – Smart and Effective

New diagnostics functions also represent a key feature of an intelligent sensor. The additional sensor data generated here lets you realize intelligent maintenance concepts to significantly improve system uptime. An operating hours counter is often built in as an important aid for predictive maintenance.

The light emission values are extremely helpful in many applications, for example, when the ambient conditions result in increased sensor contamination. These values are made available over IO-Link as raw data to be used for trend analyses. A good example of this is the production of automobile tires. If the transport line of freshly vulcanized tires suddenly stops due to a dirty sensor, the tires will bump into each other, resulting in expensive scrap as the still-soft tires are deformed. This also results in a production downtime until the transport line has been cleared, and in the worst case the promised delivery quantities will not be met. Smart sensors, which provide corresponding diagnostic possibilities, quickly pay for themselves in such cases. The light remission values let the plant operator know the degree of sensor contamination so he can initiate a cleaning measure before it comes to a costly production stop.

In the same way, the light remission value BOS21M_ADCAP_Produktbild.png allows you to continuously monitor the quality of the sensor signal. Sooner or later equipment will be subject to vibration or other external influences which result in gradual mechanical misalignment. Over time, the signal quality is degraded as a result and with it the reliability and precision of the object detection. Until now there was no way to recognize this creeping degradation or to evaluate it. Sensors with a preset threshold do let you know when the received amount of light is insufficient, but they are not able to derive a trend from the raw data and perform a quantitative and qualitative evaluation of the detection certainty.

When it comes to operating security, intelligent sensors offer even more. Photoelectric sensors have the possibility to directly monitor the output of the emitter LED. This allows critical operating conditions caused by aging of the LED to be recognized and responded to early. In a similar way, the sensors interior temperature and the supply voltage are monitored as well. Both parameters give you solid information about the load condition of the sensor and with it the failure risk.

Flexible and Clever

Increasing automation is resulting in more and more sensors and devices in plant systems. Along with this, the quantity of transported data that has to be managed by fieldbus nodes and controllers is rising as well. Here intelligent sensors offer great potential for relieving the host controller while at the same time reducing data traffic on the fieldbus. Pre-processing the detection signals right in the sensor represents a noticeable improvement.  A freely configurable count function offers several counting and reset options for a wide variety of applications. The count pulses are evaluated directly in the sensor – without having to pass the pulses themselves on to the controller. Instead, the sensor provides status signals, e.g. when one of the previously configured limit values has been reached. This all happens directly in the sensor, and ensures fast-running processes regardless of the IO-Link data transmission speed.

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Industry 4.0 Benefits

In the age of Industry 4.0 and IoT, the significance of intelligent sensors is increasing. There is a high demand from end users for these sensors since these functions enable them to use their equipment and machines with far greater flexibility than ever before. At the same time they are also the ones who have the greatest advantage when it comes to preventing downtimes and production scrap. Intelligent sensors make it possible to implement intelligent production systems, and the data which they provide enables intelligent control of these systems. In interaction with all intelligent components this enables more efficient utilization of all the machines in a plant and ensures better use of the existing resources. With the increasing spread of Industry 4.0 and IoT solutions, the demand for intelligent sensors as data providers will also continue to grow. In the future, intelligent sensors will be a permanent and necessary component of modern and self-regulating systems, and will therefore have a firm place in every sensor portfolio.

To learn more about these smart sensors, visit www.balluff.com.

The Perfect Photoelectric Sensor – Imagine No More

In my last blog, Imagine the Perfect Photoelectric Sensor, I discussed the possibilities of a single part number that could be configured for any of the basic sensing modes: through-beam, retroreflective, background suppression and diffuse. This perfect sensor would also have the ability to change the sensing mode on the fly and download the required parameters for a changing process or format change.  Additionally, it would have the ability to teach the sensing switch points on the fly, change the hysteresis, and have variable counter and time delays.

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Tomorrow is here today! There is no need to imagine any longer, technology has taken another giant leap forward in the photoelectric world.  Imagine the possibilities!

Below are just some of the features of this leading edge technology sensor. OEM’s now have the opportunity to have one sensor solve multiple applications.  End users can now reduce their spare inventory.

To learn more visit www.balluff.com.

 

Basic Color Sensor Overview

PrintIn the past, color sensors emitted light using red, green and blue LEDs’. The sensors were then able to distinguish colors using the RGB components of the reflected light back to the sensor’s receiver. As technology has progressed true color sensors have been developed that not only can compare colors but measure them more accurately than the human eye.

Color sensors are based on diffuse technology and can be compared to a fixed focus or convergent sensor because of the focused light spot. Unlike color contrast sensors that only detect the difference between two colors based on brightness, color sensors can detect a wide range of colors.

cielabTrue color sensors typically use white LED’s which allow for a greater color spectrum evaluation. Combine this with the CIELAB color system which is one of the most versatile color systems and the result is a color sensor that equals or exceeds the human eye. The CIELAB color system is a three-dimensional independent infinite representation of colors. The L component for lightness and a and b components for color are predefined absolute values. Lightness varies from black (0) to the brightest white (100). Color channel a varies from green negative 100 to red positive 100. Color channel b varies from blue negative 100 to yellow positive 100 with gray values at a=0 and b=0.

Due to the technology, color sensors can check only a small spot of color but can check this spot amazingly fast – up to 1.5 kHz in case of the Balluff’s fiber optic BFS 33M which also has a range of 400mm. Unlike a color sensor camera, which will focus on the object’s surface pattern and may cause false readings the true color sensor will ignore patterns thus providing more accurate color detection. In addition the true color sensor will have more outputs than the color camera.

Smart color cameras are working with RGB but could work also with HSV color models. They could be used to check larger areas for the same color or color codes on a part, but have slower update rate of 50 Hz. Special cameras for faster applications are available in the market but at higher costs. It is important that the light source for the smart color cameras be a white light with a standardized white balance, and that this light must kept constant for all checks to avoid errors.

The sophistication on the front end of the color sensor can be much more advanced and still remain a cost effective option for industrial use due to the fact that a camera requires a much larger processing system. The more sophisticated the sensors are in the camera the more robust the processor must be in order to process or map the data into an image.

To learn more visit www.balluff.us.

You can also request a digital copy of our Photoelectric Handbook here.

Level Detection Basics – Where to begin?

Initially I started to write this blog to compare photoelectric sensors to ultrasonic sensors for level detection. This came to mind after traveling around and visiting customers that had some very interesting applications. However, as I started to shed some light on this with photoelectrics, sorry for the pun but it was intended, I thought it might be better to begin with some application questions and considerations so that we have a better understanding of the advantages and disadvantages of solutions that are available. That being said I guess we will have to wait to hear about ultrasonic sensors until later…get it, another pun. Sorry.

Level detection can present a wide variety of challenges some easier to overcome than others. Some of the questions to consider include the following with some explanation for each:

  • What is the material of the container or vessel?
    • Metallic containers will typically require the sensor to look down to see the media. This application may be able to be solved with photoelectrics, ultrasonics, and linear transducers or capacitive (mounted in a tube and lowered into the media.
    • SmartLevelNon-metallic containers may provide the ability for the sensors look down to see the media with the same technologies mentioned above or by sensing through the walls of the container. Capacitive sensors can sense through the walls of a container up to 4mm thick with standard technology or up to 10mm thick using a hybrid capacitive technology offered by Balluff when detecting water based conductive materials. If the container is clear or translucent we have photoelectric sensors that can look through the side walls to detect the media. You can get more information in our white paper, SMARTLEVEL Technology Accurate point level detection.
  • What type of sensing is required? The short answer to this is level right? However, there are basically two different types of level detection. For more information on this refer to the Balluff Basics on Level Sensing – Discrete vs. Continuous.
    • Single point level or point level sensing. This is typically accomplished with a single sensor that allows for a discrete or an on-off signal when the level actuates the sensor. The sensor is mounted at the specific level to be monitored, for instance low-low, low, half full (the optimistic view), high, or high-high. These sensors are typically lower cost and easier to implement or integrate into the level controls.
    • Example of in-tank continuous level sensor
      Example of in-tank continuous level sensor

      Continuous or dynamic level detection. These sensors provide an analog or continuous output based on the level of the media. This level detection is used primarily in applications that require precise level or precision dispensing. The output signals are usually a voltage 0-10V or current output 4-20mA.  These sensors are typically higher cost and require more work in integrating them into system controls.  That being said, they also offer several advantages such as the ability to program in unlimited point levels and in the case of the current output the ability to determine if the sensor is malfunctioning or the wire is broken.

Because of the amount of information on level detection this will be the first in a series on this topic. In my next blog I will discuss invasive vs non-invasive mounting and some other topics. For more information visit www.balluff.us.

Photoelectric Basics – Distance Measuring

Some photoelectric applications require not only knowing if the object is present or not but exactly where the object is while providing a continuous or dynamic value representative of the objects location.  For instance, if a robot is stacking a product is the stack at the correct height or how many additional pieces can be placed on the stack, how large is the coil or roll diameter of a product, and how high is the level or how much further can the product move before it is in position.  Distance sensors can provide this dynamic information and in some case provide a digital output as well for alarms.

RetroreflectiveThese sensors are normally based on diffuse sensing technology. However, in some cases retro-reflective technology is used for extremely long sensing distances.  As with diffuse sensors there is only one device to mount and wire.  However, due to the technology required for the higher resolutions, lensing, electronics and outputs these devices are typically much more expensive than a discrete diffuse sensor.

Similar to a diffuse sensor the distance sensor emits a pulsed light that strikes an object and a certain amount of light is reflected back to the sensor’s receiver.  The sensor then generates an analog output signal that is proportional to the distance to the target.  The technology that is utilized within the sensor to determine the distance is either Time of Flight or Triangulation.

PrintTime of Flight sensors are more immune to target color and texture than light intensity based system because of the time component.  These devices measure greater distances than the triangulation method however there is a sacrifice in resolution.

PrintTriangulation sensors emit a pulsed light towards the target object.  The light is then reflected back to the receiver.  When the light reaches the sensor it will strike the photosensing diode at some angle.  The distance between the sensor and the target determines the angle in which the light strikes the receiver.  The closer the target is the sensor the greater the angle.
Triangulation based sensors being dependent on the amount of reflected light are more susceptible to target characteristics such as color and texture.  These sensors are characterized by short to mid-range sensing distance however they provide higher resolutions than TOF sensors.

Output signals are either 0…10 volts, 1…10 volts or 4…20mA each of which has their pros and cons.  Voltage outputs, 0 – 10 or 1- 10 volts, are easier to test and there is typically a broader offering of interface devices.  However voltage outputs are more susceptible to noise from motors, solenoids or other coils and voltage drops of the wire.  In addition generally voltage output cable runs should be less than 50 feet.  Also since 0 volts is an acceptable output value broken wires, device failures, or power failures can go undetected.

Current outputs, 4 – 20 mA, provide the best noise immunity, are not affected by voltage drop and the cables lengths can exceed 50 feet.  Since the sensor will be providing 4mA at zero distance its lowest possible signal, if the sensor should fail, the cable damaged or a power failure the interface device can detect the absence of the signal and notify an operator.  Current outputs are more difficult to test and in some cases are affected by temperature variations.

For more information about photoelectric sensors, request your copy of Balluff’s Photoelectric Handbook.

Photoelectric Output Operate Modes and Output Types

Photoelectric sensors are used in a wide variety of applications that you encounter every day. They are offered in numerous housing styles that provide long distance non-contact detection of many different types of objects or targets. Being used in such a variety of applications, there are several outputs offered to make integration to control systems easy and depending on the sensing mode when the output is activated in the presence of the target.

DiffuseDiffuse sensors depend on the amount of light reflected back to the receiver to actuate the output. Therefore, Light-on (normally open) operate refers to the switching of the output when the amount of light striking the receiver is sufficient, object is present. Likewise, Dark-on (normally closed) operate would refer to the target being absent or no light being reflected back to the receiver.

RetroreflectiveRetroreflective and through-beam sensors are similar in the fact they depend on the target interrupting the light beam being reflected back to the receiver. When an object interrupts the light beam, preventing the light from reaching the receiver, the output will energize which is referred to as Dark-on (normally open) operate switching mode or normally open. Light-on (normally closed) operate switching mode or normally closed output in a reflex sensor is true when the object is not blocking the light beam.

signalsOutputs from photoelectric sensors are typically either digital or analog. Digital outputs are on or off and are usually three wire PNP (sourcing output) or NPN (sinking outputs). The exception to this is a relay output that provides a dry or isolated contact requiring voltage being applied to one pole.

Analog outputs provide a dynamic or continuous output that varies either a voltage (0-10 volt) or current (4-20mA) throughout the sensing range. Voltage outputs are easier to integrate into control systems and typically have more interface options. The downside to a voltage output is it should not be ran more than 50 feet. Current outputs can be ran very long lengths without worry of electrical noise. As additional advantage of the analog output is that it has built in diagnostics, at its minimum there will always be some current at the input unless the device completely fails or the wire is damaged.

Some specialty photoelectric sensors will provide a serial or network communication output for communications to higher level devices. Depending on the network, IO Link, for instance, additional diagnostics can be provided or even parameterization of the sensors. io-link
Interested in learning more about photoelectrics basics? You can also request a copy of the new Photoelectric Handbook.

Detecting Small Bubbles? Consider These Factors First

BubbleDetectionBubble or air-in-line detection is a common lab automation application. In these types of applications it’s important to know whether or not liquid is flowing through a line to ensure safe and proper function in liquid-handling processes.  As these processes utilize smaller and smaller volumes of liquid — which provides cost and time saving benefits — it becomes more and more difficult to detect the potential air pockets forming inside the line. The most common approach in detecting these minute air pockets is a through-beam, photoelectric bubble sensor.

Photoelectric bubble sensors provide non-invasive detection of fluids and air pockets residing inside a tube. They have fixed opening dimensions for standard tube sizes allowing the selected tube to sit in perfect position between the sensor’s optical components. When the sensor’s light beam is blocked by fluid (or an air pocket) inside the tube, the received signal varies and external electronics determine if the signal variation is above or below the set threshold. Once the threshold is met the sensor’s output is switched.

Detecting bubbles sounds quite straightforward and simple, but in reality the application can be somewhat complicated. Several factors should be considered for reliable detection. Listed below are a few factors to consider:

  1. Tube diameters (inner and outer)
  2. Tube transparency
  3. Liquid type(s)
  4. Liquid transparency

Tube Diameters

Tube Sensor DrawingBecause a tube acts as a lens for light to travel it’s important to factor in the tube diameters. If there is a large difference between the outer and inner diameters of a particular tube, the outcome is a relatively large tube wall. A large tube wall will allow light rays to travel from the emitter through the wall straight to the detector without passing through the inner diameter of the tube, where the liquid or bubble is present. This causes unreliable detection. By accounting for both the inner and outer tube diameters a proper determination can be made in selecting what type of sensor to use to ensure that light only passes through the inner diameter of the tube and not through the wall.

Tube Transparency

Since photoelectric tube sensors operate on the principle of light detection, light must make it through one end of the tube and out the other end. Therefore, the transparency of the tube is critical. If the tube is opaque a photoelectric sensor solution is unlikely; however, in some cases it’s possible for a photoelectric tube sensor to detect through an opaque tube.

Liquid Type(s) and Transparency

The liquid type(s) and transparency are critical when determining which photoelectric tube sensor to use. If the liquid type is non-aqueous, without factoring in its transparency, it’s best to use the principle of light refraction through the liquid. If the liquid type is aqueous and is completely transparent or semitransparent, it’s best to use the principle of light absorption through the liquid. The following table will help determine what type of sensor to use with respect to the liquid type present inside the tube.

BubbleSensingChart

Since the type of applications that require precise bubble detection range in specifications from the use of hundreds of different liquids to specialized tube dimensions, this post only touches the surface of the photoelectric sensors for bubble detection.  For more information on tube sensors, please visit the Balluff website.

Precision Optical Measurement and Detection

In applications that require precise measurement and detection of one or more objects, what type of sensor should one use? If objects that are very small and far apart need to be detected, what type of sensor provides high resolution over its entire sensing range?

The answer: a laser micrometer.

A laser micrometer can identify, compare, or sort objects based on minimal size or height differences. Similar to a standard micrometer caliper, a laser micrometer provides precise measurements.

But how is this done exactly? Let’s find out!

A laser micrometer consists of two opposed sides, a transmitter side and a receiver side. These two sides sit opposite of each other to detect any object that enters in-between them.

On the transmitter side, a laser light source is positioned so that its emitted light enters a lens. The lens then collimates the light from the laser by refraction into a collimated beam of light (see Figure 1). By definition, a collimated light beam is a light beam where each light path in the beam is travelling parallel to one another. This collimated light beam has minimal divergence, even over large distances.

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Figure 1

On the other side, the receiver side, a CCD (charge-coupled device) is positioned to collect the light emitted from the transmitter side. CCDs are made up tiny light-sensitive cells. These cells convert the amount of light intensity received into a corresponding electric charge, which can then be measured (see Figure 2).

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Figure 2

The combination of these two components, a collimated light beam and a CCD, make up the foundation of a standard laser micrometer. The collimated light beam, which consists of a homogeneous light band, is directed at the CCD, which consists of hundreds of tiny light-sensitive cells. With this configuration, even a slight change in an object (e.g., its diameter, height, position, etc.) causes a change in the object’s corresponding shadow that is projected onto the CCD. This slight change can then be measured.

A few examples of the measurement capabilities for a laser micrometer are listed below, along with a video.

Position_BLA
Position Monitoring
Diameter_BLA
Diameter Detection
Gap_BLA
Gap/Height Measurement
Edge_BLA
Edge Guide — even with semi-transparent materials

The following video showcases the capabilities of the Balluff Light Array sensor: http://www.youtube.com/watch?v=btumxuIgj_4.

The Other Retro-Reflective Sensors

Most of the time when we think of Retro-Reflective sensors the first thing that comes to mind is a photoelectric sensor. Photoelectric offerings use a reflector to reflect light from the internally mounted emitter and receiver. Retro photoelectric sensors come in many form factors with light source options such as infrared, red light and laser types.

Ultrasonic sensors are commonly forgotten when reflective sensors are needed in a particular application. Ultrasonic sensors when set up in “Window Mode” are similar to a photoelectric sensor however the ultrasonic sensor can use an existing background as the reflective surface such as a metal plate or a solid background. The sensor simply returns a signal as soon as an object fully covers the reflector. This mode is ideal for detecting difficult targets that photoelectric sensor can have trouble with such as poorly reflective materials

ultrasonicThe example shows an Ultrasonic sensor set up in window mode. The sensor is sending a sound wave to the background (reflector) so a target can be detected when entering the detection area between the sensor and the reflector background.

For more information Ultrasonic sensors, click here.