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Pepperl+Fuchs Blog

Ultrasonic Sensors for Automated Spray Control

Posted by Marcel Ulrich on Tue, Feb 25, 2014

Car wash automation

In automated wash processes, the large dimensional disparity between subcompacts, low-riding sports cars, and large pick-up trucks makes it difficult to effectively clean vehicles with a fixed-position spray system.

Ultrasonic sensors for spray control
To customize the cleaning for each unique make and model, ultrasonic sensors must locate and position the vehicle, as well as acoustically profile its contour.

Once the body is scanned, the mapped data can be used to optimize the sprayer/towel/brush-to-vehicle distances. Sprayers and soft-cloth scrubbers can then maintain a consistent distance as they wrap around the car/truck, ensuring even coverage while preventing sprayer-vehicle contact.

5 reasons ultrasonic sensors are best-suited for car wash automation

  1. Indifference to color – Ultrasonics detect vehicles of any color with identical accuracy
  2. Continuous positional feedback - Analog output models provide a high-resolution, continuous profile of the vehicle body
  3. Wide evaluation beam – The inherently wide ultrasonic beam can profile the vehicle body without losing its signal due to wheel wells, indentations, and gaps
  4. Contaminate immunity – Dirt and films have no effect on the transducer, nor do airborne mists 
  5. Long-range detection – sensing distances to 14 feet allow sensors to be mounted out of harm’s way while still providing millimeter-precise positional data

Side profiling

To properly profile a vehicle, it must be scanned from both the side and overhead. As a vehicle pulls into the bay area, two opposing analog ultrasonic sensors scan across the bay’s travel path and detect the vehicle “nose.” As it pulls forward, the entire length of both sides is then mapped. The subsequent data is used by side sprayers to apply a consistent rinse and wash.

Overhead profiling

Overhead-mounted sensors provide hood, roof, trunk, and/or bed data. It should be noted that steeply angled, smooth window surfaces may completely deflect the sound sideways, preventing its return to the transducer. Such lost window echoes are typically accounted for in the controller’s evaluation algorithm.

Performance in environmentally challenging areas

Ultrasonic sensors are best suited for mounting near the bay entry, outside the heavy soap suds and pressure washing of the central cleansing area. While 24/7 exposure to high humidity should be avoided, daily exposure to the moisture and humidity associated with car washes is not a problem for appropriately rated models. An environmental protection classification of IP67 (or better) is sufficient for most applications, as the bay door opening/closing and overnight downtime keep the sensor sufficiently “dry.”

Synchronization options for mounting in confined spaces

A concern with multiple ultrasonic sensors in a confined area is cross-talk, where a sensor mistakes the evaluation pulses of other nearby models as its own (i.e., where overhead sensors profile the hood/roof/trunk as units mounted immediately below profile the sides). Most manufacturers offer models with synchronization features that eliminate cross-talk. In slow processes, each sensor can be polled individually (accomplished by simply interconnecting their synch inputs). If the cycle time for one-sensor-at-a-time polling is too slow, the sensors can also be placed in a master/slave mode, where all interconnected sensors are strobed simultaneously. This effectively reduces the cycle time of up to 10 units to that of a single sensor.

Other applications for ultrasonic spray control

It is not simply vehicle washing that benefits from ultrasonic-based control. From farming to automotive assembly, ultrasonic feedback controls a variety of spray processes.

Outdoor environments

Beyond the realm of consumer vehicles, agricultural machinery utilizes ultrasonics to control boom height when spraying farm fields, ensuring consistent, even coverage regardless of the field contour.

Ultrasonic sensors for agricultural machinery
Golf course machinery also uses ultrasonics to follow the undulating course topography and evenly apply fertilizer and pesticide solutions.

Paint processes

Ultrasonics are used to profile vehicle contour prior to entering a paint-spray environment. For example, before a pick-up truck enters the paint booth, it can be ultrasonically confirmed as a step-side or fleet-side model.

Ultrasonic sensors for paint booths

Conclusion

If your automated spray process requires continuous broad-beam target scanning that’s immune to color variances and environmental contaminates, give ultrasonic sensing a try. There are many off-the-shelf models available to do the job.

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Topics: Applications, Ultrasonic Sensors

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