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.

There’s more than just one miniature sensor technology

As I discussed in my last blog post, there is a need for miniature, precision sensors. However, finding the right solution for a particular application can be a difficult process. Since every sensor technology has its own strengths and weaknesses, it is vital to have a variety of different sensor options to choose from.

The good news is that there are several different technologies to consider in the miniature, precision sensor world. Here we will briefly look at three technologies: photoelectric, capacitive, and inductive. Together these three technologies have the ability to cover a wide range of applications.

Photoelectric Sensors

MiniPhotoelectricPhotoelectric sensors use a light emitter and receiver to detect the presence or absence of an object. This type of sensor comes in different styles for flexibility in sensing. A through-beam photoelectric is ideal for long range detection and small part detection. Whereas a diffuse photoelectric is ideal for applications where space is limited or in applications where sensing is only possible from one side.

Miniature photoelectric sensors come with either the electronics fully integrated into the sensor or as a sensor with separate electronics in a remote amplifier.

Capacitive Sensors

MiniCapacitiveCapacitive sensors use the electrical property of capacitance and work by measuring changes in this electrical property as an object enters its sensing field. Capacitive sensors detect the presence or absence of virtually any object with any material, from metals to powders to liquids. It also has the ability to sense through a plastic or glass container wall to detect proper fill level of the material inside the container.

Miniature capacitive sensors come with either the electronics fully integrated into the sensor or as a sensor with separate electronics in a remote amplifier.

Inductive Sensors

MiniInductiveInductive sensors use a coil and oscillator to create a magnetic field to detect the presence or absence of any metal object. The presence of a metal object in the sensing field dampens the oscillation amplitude. This type of sensor is, of course, ideal for detecting metal objects.

Miniature inductive sensors come with the electronics fully integrated into the sensor.

One sensor technology isn’t enough since there isn’t a single technology that will work across all applications. It’s good to have options when looking for an application solution.

To learn more about these technologies, visit www.balluff.us

5 Tips on Making End-of-Arm Tooling Smarter

Example of a Flexible EOA Tool with 8 sensors connected with an Inductive Coupling System.

Over the years I’ve interviewed many customers regarding End-Of-Arm (EOA) tooling. Most of the improvements revolve around making the EOA tooling smarter. Smarter tools mean more reliability, faster change out and more in-tool error proofing.

#5: Go Analog…in flexible manufacturing environments, discrete information just does not provide an adequate solution. Analog sensors can change set points based on the product currently being manufactured.

#4: Lose the weight…look at the connectors and cables. M8 and M5 connectorized sensors and cables are readily available. Use field installable connectors to help keep cable runs as short as possible. We see too many long cables simply bundled up.

#3: Go Small…use miniature, precision sensors that do not require separate amplifiers. These miniature sensors not only cut down on size but also have increased precision. With these sensors, you’ll know if a part is not completely seated in the gripper.

#2: Monitor those pneumatic cylinders…monitoring air pressure in one way, but as speeds increase and size is reduced, you really need to know cylinder end of travel position. The best technology for EOA tooling is magnetoresistive such as Balluff’s BMF line. Avoid hall-effects and definitely avoid reed switches. Also, consider dual sensor styles such as Balluff’s V-Twin line.

#1: Go with Couplers…with interchangeable tooling, sensors should be connected with a solid-state, inductive coupling system such as Balluff’s Inductive Coupler (BIC). Avoid the use of pin-based connector systems for low power sensors. They create reliability problems over time.

Trending Now: Miniature Sensors

Celebrating the Holiday season is one of my favorite times of the year. Some of the common activities I enjoy include spending time with family and friends, eating a tremendous amount of food (and wondering afterward why I do this to myself year after year), and giving and receiving a few presents. Let’s focus on the presents aspect for a second. The bigger the present the better, right? Well, we know that’s not always the case. That smaller present could very well be the perfect gift.

minifamilyNow let’s shift gears and look at manufacturing. There is a trend in manufacturing, in general, toward miniaturization. Earlier this year I was shown a website, MICRO Manufacturing, that looks across different industries to see how the miniaturization trend is being engaged. One of the more obvious cases is in consumer electronics. It all started taking off with the desktop computer. Following the desktop computer was the laptop. And in the past few years we’ve seen the rise of smartphones and tablets. Now we’re beginning to see smart wearable devices (watches, fitness trackers, glasses, etc.). Who knows what will happen next? I bet we could take a good guess: it’ll be something even smaller.

As manufacturing continues in this direction, the demand for miniature sensors grows. However, miniature sensors aren’t just defined by their small form factor, but also by their precision. Miniature sensors are developed with a clear purpose to meet these manufacturing requirements. For more information, please click here.

And, just like that small present during the Holidays, a miniature, precision sensor could be the perfect solution.

Meeting the Challenges of Precision Sensing: Very Small Target Displacement

Fundamental application problem: Inductive prox sensor is latching on (or…failing to turn on)

  • The prox sensor gap is set to turn on when the target approaches, but it does not turn off when the target recedes (latching on)
  • The prox gap is opened up until sensor turns off at maximum target approach, but it fails to detect the target upon the next approach cycle
  • The prox sensor gap is set to turn on when the target approaches, but later on the operation becomes intermittent (prox fails to reliably detect the target)

Solution: High-performance miniature inductive prox sensor

Critical sensing performance specifications:

o   Low variation of switch point from sample to sample
o   Tight repeat accuracy of switch point
o   Low temperature drift of switch point
o   Low maximum hysteresis (distance between switch-on to switch-off)

Continue reading “Meeting the Challenges of Precision Sensing: Very Small Target Displacement”

Automated Assembly Lines Are Shrinking

There is a common trend in the market for smaller more efficient assembly machines. Machine builders and end users are challenged with faster moving, smaller production lines that require smaller sensors and brackets. Balluff has a compete line up of miniaturized sensors. Let’s take a look below of a common challenge for high acceleration machine movement and how miniature sensors can provide a solution.

 miniappCustomer Demands: 

  • Anything mounted to the moving mechanism must be low mass
  • Added mass reduces acceleration  capability of a given motor and drive system
  • Added mass increases motor and drive size requirements to meet acceleration specs (cycle times) driving cost up
  • Large motors increase energy consumption which makes the machine less competitive in the market (less efficient)
  • Conventional sensors and brackets are much too heavy (and usually…too large) to meet this challenge

Solution:

  • minipennyIncredibly miniaturized, self – contained inductive sensors
  • Miniature size = inherently low mass
  • Corresponding tiny brackets = inherently low mass
  • Totally self – contained electronics = zero space taken up by separate amplifier or electronics
  • Miniaturization of sensors allow installation in compact tooling where previously nothing would fit
  • Enhances the level of machine automation/control that customers can achieve for their machines

Stay tuned for more information on how other sensor technologies can be implemented into smaller assembly machines. For more information on mini sensors, click here.

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Save Space with Miniature Rectangular Proximity Sensors

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Historically the most popular selling housing style for an inductive proximity sensor has been the tubular style.  The more popular sizes tend to be M8, M12, M18 and M30.  Smaller tubular sizes of 3 mm, 4 mm, M5, and 6.5 mm are also available and have seen increased sales in the most recent years.  One issue that may affect a tubular sensor’s application is its length.  Most standard models are 50 mm to 65 mm long while some shorter body types may be in the 30mm range.  What if your application requires 1.5 to 3 mm of sensing range, but you only have 10mm of depth to allow for the sensor?  Try looking at a block or rectangular style inductive proximity sensor.

Continue reading “Save Space with Miniature Rectangular Proximity Sensors”