Fit for the purpose under the most difficult conditions

Robust encoders enable high-precision position sensing in harsh environments

Encoders for heavy industry must not only detect the position of objects with pinpoint accuracy, they also have to be very robust. Hengstler GmbH has been supplying numerous industries with encoders and resolvers for heavy duty applications for decades. Even severe impacts, high temperatures and salt water cannot harm their encoders.

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Down here in the mine, it's noisy and very dusty. There is a monstrous machine with two rotating wheels milling its way incessantly along the excavation face. The disk shearer planes strips of coal out of the seam with its cutters, and the coal then falls onto a chain conveyor to be transported away. Anyone watching this huge machine at work will hardly believe that it would not function without a comparatively tiny component. We are talking about a small encoder that detects the position of the rollers and the drive. The encoder sends a signal to the shearer control system, which then readjusts the alignment of the cutting rollers to the seam. This guarantees that the machine achieves the greatest possible extraction performance.

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The encoders used have to withstand a lot: a dusty atmosphere, temperatures above 40?°C, vibrations and shocks as well as humidity caused by mine water put considerable stress on the encoders.

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Absolute encoders ensure precision in coal mining

As a result, well-known manufacturers of mining machines use the ACURO AX65 multiturn encoder from Hengstler in their shearers. The absolute encoder is not only shock-resistant up to 200?g, but with an outer diameter of just 65 mm, it is also the smallest encoder in its class. Hengstler has had the AX65 specially certified for applications in potentially explosive environments and in mining (ATEX/IECEx). With its high-quality stainless steel housing, the encoder not only withstands extreme temperatures from -40 to +60?°C, it is also extremely corrosion-resistant.

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Some product features are unique on the market

The high resilience of the encoder is achieved through several innovative design measures. These include the captive screws that are located within the explosion-proof installation space of the encoders and are sealed by an O-ring. This means that there is no gap between the screw head and the encoder through which moisture could penetrate. Comparable encoders on the market have neither this seal nor captive screws.

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The hermetic sealing of the screw heads not only has the advantage that the encoder cannot corrode inside, it also prevents dirt from sticking to the screws, which would make them seize. That is why it is still possible to loosen the screws even after a long time.

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Precise positioning of drill heads

With their high corrosion protection and tremendous physical robustness, ACURO AX65 encoders are also recommended for use in drilling applications – e.g. on drilling platforms, drilling vessels and in geothermal exploration. In these contexts, they take on several tasks simultaneously. On the one hand, the encoders in the drive unit of the drill string – the top drive – measure the range of travel. The exact position of the drill string is required when connecting pipes of different lengths, to name just one application. In combination with wire rope hoists, the encoder also records the length measurement for the travel path of the top drive.

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Another area of application for the AX 65 on oil platforms is pipe handling. The term refers to the removal of the individual segments of drill pipe from a storage system and transfer to an automated assembly system. These robots, called "electric roughnecks", screw the individual rods together to form a drill string. Here, too, the ACURO AX65 comes into its own: it is not only shock-resistant, but also withstands axial and radial shaft loads of up to 300?N. And last but not least, the encoders are modular, so that the customer can attach his own cables.

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Only a few encoders have EX certification

The extensive explosion protection provided by the Hengstler encoders was also a convincing factor with Herrenknecht Vertical GmbH. The company was looking for an encoder to position the top drive and lifting unit of its deep drilling rigs and chose the ACURO AX71 and ACURO AX73. "Very few suppliers have ex-protected encoders in their range of products," says Jürgen Binder, Technical Manager at Herrenknecht Vertical, citing one of the reasons for his choice. In addition, both encoders also scored in terms of field suitability: they offer very good EMC and lightning protection, withstand extreme temperatures (-40?°C/ +70?°C) and, like the AX65, are corrosion-resistant.

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Condition monitoring ensures optimum functionality

The operating status of the Hengstler encoders can also be monitored at any time. For the absolute encoders, existing interfaces such as SSI and Profinet enable the encoders to self-monitor. The incremental encoders, on the other hand, have an optional alarm output. "If the temperature range of the encoder is exceeded or an LED becomes clogged, the encoder automatically sends a signal to the controller," says Application Manager Peter Elbel.

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Bespoke adaptations are standard for Hengstler

Hengstler can also modify any of its encoders exactly according to customer requirements. That service was used by a company that manufactures scarfing machines for the steel industry. These systems remove surface defects on the steel ingots produced in the casting process. In order for the scarfing torches to work efficiently, they must be precisely aligned with the surface to be processed. The ICURO RI58TD incremental encoders from Hengstler are used here: they detect both the exact position of the scarfing torches and their travel speed.

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The incremental encoders are themselves very robust, withstanding temperatures of up to 100?°C and shocks of up to 100?g. In addition, the engineers equipped the encoder with a particularly heat-resistant cable that does not deform, even at ambient temperatures of up to 300?°C.

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Suggestions from customers are incorporated in product design

The adaptation of encoders to a wide variety of applications is a matter of course for Peter Elbel and his team. In addition to the installation of special cables, Hengstler's service also includes the expansion of temperature ranges, the increase of bearing loads and the integration of special seals. "Thanks to our many years of expertise, we can provide our customers with exactly the solutions they need," says Elbel.

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The product range that he and his colleagues have at their disposal is huge. In addition to its own absolute and incremental encoders, Hengstler also sells heavy-duty incremental encoders and resolvers made by its US sister company Dynapar. Since the resolvers consist exclusively of windings and do not contain any sensitive evaluation electronics, they are particularly well suited for applications with extreme ambient temperatures or severe shocks or vibrations. "Compared to the competition, we have by far the largest range of heavy-duty resolvers," says Application Manager Peter Elbel .

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As an engineer, he knows the requirements of heavy industry well – he and his department have already taken up numerous suggestions from the industry and optimised Hengstler encoders accordingly. The captive screws and the O-ring seals are just two of many examples.

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The broad product range offers many options

Whether incremental encoders for high-temperature applications, corrosion-resistant and explosion-proof absolute encoders or resolvers with maximum shock resistance: Hengstler finds the ideal solution for every heavy industry application. And if a standard product is not one hundred percent suitable, it is modified without further ado.