Sensors to detect vehicle height from the side

Question

I am looking for a way to determine vehicle height measured from the side. The application is for a drive-through ATM, the sensors being mounted inside the ATM enclosure.

Some ATMs have a roof as well, in those cases the solution would be straightforward - ultrasonic sensor (emitter and detector) mounted in the roof, measuring distance to vehicle roof, and with a known distance to ground, the height could be calculated. But I need a solution that works in all cases.

I want to preferably avoid any detectors or emitters outside the ATM enclosure, such as an ultrasonic sensor on a pole sticking out the top of the ATM, or a detector on the far side.

One solution is to have an array of ultrasonic sensors arranged vertically inside the ATM enclosure. This will require experimenting with the spacing between sensors, and knowing the overlap in each sensor's 'field of view'.

The application is outdoors, with large temperature variations, which is why I looked at ultrasonic sensors first. I'd like to know if something else may work better in a cost-effective manner.

If someone one wants to see what a typical drive through ATM looks like:

Answer 1

I would use only one or two ultrasonic sensors at different angles placed on the top of the ATM, two to get around with an open window on the driver side.

Use the fixed lower sensor to detect a vehicle presence , wait a bit to allow the vehicle to stop then move up the ATM if a proximity is detected by the top ultrasonic sensors or move down if not, until something changes then adjust the height according to your knowledge on vehicle height vs top roof height and stop.

A must is a manual control available at any level (parallel UP and DOWN switches at many levels) to allow the driver to adjust the height at a comfortable level.

You can make the machine learn from user input where to place the ATM for different top roof heights improving the automatic height adjustment in time combining the readings from the fixed sensor and top sensors and user input for similar previous values.

Don't do that without a driver available manual control, in case of a failure placing the ATM at an accessible level he will be in an funny impossible situation, he cannot open the door since is obstructed by the ATM.

Take care also about the side mirrors, the ATM might be at a lower height when the vehicle stops, maybe an obstacle before the ATM to prevent the vehicle to stop to close or some flexible roof extension on the top.

Of course , the ultrasonic sensors must be used one at the time, the lifting is slow so you can live with that.

Answer 2

Try this

^{simulate this circuit – Schematic created using CircuitLab}

Offset the two sensors by 6". This allows the Range^2 and (Range+6")^2 to give you some useful distance information.

The two diodes after the photodiodes will generate the LOG (beware, temperature sensitive) and greatly extend the dynamic range.

Have one of these every foot of vertical distance.

Answer 3

Your best bet will probably be some sort of “visual” sensor, namely sensors that react to transmitted or reflected light. These could be:

• A camera (or two) with or without IR illumination, that feed into custom software to measure a well-defined area of the image.
• An electro-optical assembly (e.g., LIDAR) that scans the area in front of the ATM.
• A few linear optical arrays (basically 1-D tall cameras) that provide transmitted or reflected light information.
• At least two strategically placed optical distance (parallax/trigonometric) sensors, to sense the roof from as high an angle as possible.

I believe the least expensive, and most reliable solution might be the camera. As most of the cost would be in the software, but stereo vision is rather common in robotics, so there are a lot of projects out there Here is a project that could get you started.

Low resolution 1-D optical arrays can be constructed from discrete devices and can be placed in the movable portion of the ATM to “scan” for the location of the roof.

Parallax sensors can be built from a laser and a 1-D optical array. But these are rather common in industrial applications.