miniature sensors enable new applications

8 July 2019

Damien Wittwer, Director Product Management & Business Development, Contrinex explains that resource-saving, compact design is increasingly gaining acceptance in automation technology. Even when little space is available, full functionality must still be maintained. This is particularly true for sensors, which have important functions as the "eyes" of automation in devices and machines. For photoelectric sensing in confined installation conditions, it is usual to lay fiber-optic cables up to the actual sensing site, which is quite costly. Today, miniaturization makes it possible to accommodate high-performance sensors, including evaluation, inside compact housings with practically the same installation space. This saves installation time and simplifies setup, while IO-Link simplifies parameterization during operation. As a result, it is often possible to implement new applications.

The devil is in the detail, as the saying goes, and with small sensors it is the detail that make the important difference. Miniature sensors have been on the market for quite some time, but Contrinex has now improved essential details of its miniature sensor series and, as a result, is opening up many new applications that previously could only be solved using fiber optics or workarounds. Today, these tiny devices only differ from their larger siblings in size and not in performance. All photoelectric sensor models now have new focusing optics made of PBT/PMMA and thus achieve a higher resolution. Integrated data evaluation and an IO-Link connection for data transmission and remote configuration complete the new sensors, making installation, setup and commissioning much easier than before. In addition, since the sensors are mass-produced, they are also an economical alternative to previous fiber optic sensors with their complex technology. The new features open up a whole new range of applications for miniature photoelectric sensors in a wide variety of applications.

When space is at a premium

Maintaining precise detection even in cramped conditions is a challenge. Small devices such as mini grippers, complex systems or robot arms in particular require extremely tight switching tolerances and offer hardly any space for sensors. Sensors with a diameter of only 4 mm can be integrated into even the smallest grippers and fit into narrow gaps. The previous alternative with fiber optic cables is therefore obsolete with a few exceptions. In addition, everything is combined in one compact housing; the time-consuming selection of laser optics, application-specific fibers and matching optics as well as a separate evaluation module is no longer necessary. In contrast to optical fibers, just one extremely flexible electrical cable is installed, which allows even the narrowest bending radii. This increases reliability and saves considerable installation and maintenance costs.

Room in the tightest conditions

How do miniature sensors prove themselves in practice? A common problem is the optimal positioning of the sensor. A given function must be checked, but the sensor itself must not impair the function. Often, modifications to an existing system are necessary in order to accommodate the sensor. Naturally, the small sensors offer clear advantages here. In one application, for example, standard sensors were being used to detect semi-transparent plastic packaging. Originally, a slot of about 5 mm in width had to be widened to about 12 mm in places to accommodate the standard sensor, at considerable cost and time. By using a photoelectric miniature sensor with a 4 mm diameter, this widening work is no longer necessary, the tiny unit can easily "look" through an existing opening.

The problem cannot always be solved by a simple modification. In many cases, space is simply too limited for conventional sensors. In addition, for example, when using dynamic movements in robot arms or transport systems, etc., there is a requirement for the smallest possible mass combined with flexible connecting cables that permit the tightest bending radii over the long term. The smaller the sensor, the simpler the task of finding an optimum location. In a system for transporting electronic components, for example, these photoelectric miniature sensors have been integrated into each individual gripper element, where they reliably detect the presence and correct position of inserted parts.

Small "eyes" for medical technology

Automation saves valuable time and therefore costs in everyday medical practice, especially during standard laboratory operations. However, the devices used are subject to the highest quality requirements, as the health and lives of the patients depend on them. The miniature sensors can also play to their strengths here. In a transport system for clinical laboratory automation, the sensors have to monitor the proper function from below, i.e. the respective position of carrier platforms, similar to the location display for wagons in the freight station. The small sensor dimensions make it possible to adapt the conveyor path to the function, regardless of the possible installation of the sensor.

In another application example from the assembly industry, small plastic parts must be detected in an automatic transport device. At the end of each cycle, it is necessary to ensure that all pockets of the holder are empty to avoid production issues. The parts, which are only a few millimeters in size, are optically detected and removed if necessary. The challenge here: little space for sensors due to many small holders in a confined space and the simplest possible bundling of the connecting cables on the movable base carrier. Here, the optical mini-sensors offer the advantage of reliably detecting small areas in the smallest of spaces. They are still smaller than the objects to be measured and thus fit into the functional system design without compromise.

Small but powerful

The examples shown only give a small insight into the application possibilities of these mini-sensors. They are also in demand in many other areas, solving problem in existing systems due to their performance features. Despite an external diameter of only 4 mm or M5 in threaded versions, the photoelectric sensors offer large, pre-calibrated detection ranges of 12, 24, 60 or 120 mm in the diffuse sensing version. As through-beam sensors, up to 600 mm can even be achieved. The robust stainless steel housing with specially sealed connection offers IP67 protection as standard. Since the sensors now work with visible red light, setup is child's play compared to the earlier infrared light: WYSIWYG (What-You-See-Is-What-You-Get) for sensors. The switching frequency has been increased again and can now be set from 500 to 2,500 Hz. This allows the evaluation electronics, for example, to reliably detect fine wires at high throughputs. Depending on the sensor version, the focus of the light spot is, for example, only 5 mm in diameter at a distance of 10 mm, ideal for detecting even small parts. All miniature sensors are equipped with robust, environmentally friendly PUR cables, can be assembled with different connections and operate in the range of -25 to +65°C (-13 to +149°F)

Inductive sensors are now also available as miniature types with diameters of 3 and 4 mm and housing lengths of only 12 mm. These so-called MiniMini types (DW-AD-623-03-960) with a switching distance of 1 mm offer particularly high repeat accuracy and precision in the smallest space. Sophisticated machine tools are the main area of application, since small sensors require fewer compromises in machine design. Even in miniature grippers the small size of MiniMini sensors means that they will almost always fit in the right place to monitor the presence and position of small metallic parts, with counting and quality control, but without additional design costs.

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