Sensor passive detection

What environment is the rope used in?

Warren,

You could also look into rotary pulse generators. Attached to the pulley or somewhere on the rope, the device will rotate, generating pulses. Then you can could the pulses and see how far the rope has travelled. This device acts almost like an optical encoder.

RFID has an increasing accuracy problem directly proportional to the distance it's being sensed. But I like the idea of wireless, bounce back, detection. What is the maximum distance you have to sense?

Cabe

Hello Warren,

This is Chris Pinter.  I am an RF engineer with Pinter Electronics Consultants.

I think radios are a great way to solve problems when wires can affect results.  Wireless solutions typically cost more than wired ones and the quality of the communication link is dependent on many factors that a wired solution does not have to consider.

For your problem, I think maybe a different type of solution is better.    I would attach a magnet to the rope as a sensor.   The magnet will be more robust then a plastic box with an RFID or radio transmitter.   The magnet is also a passive device. You can then use a simple solenoid mounted on the pulley.  When the magnet passes the solenoid it turns to motor off causing the rope to stop.

Now, because I love radios so much I should mention that you can use a wireless system to transmit the signal from the pulley to the motor but a wire will be able to send the signal to the motor just as well.

Hope this helps.

Chris Pinter

When your radio absolutely must work...Choose a specialist...Choose the Best.

Pinter Electronics Consultants

http://www.pinterec.ca

It is a rider retrieval system on a giant bridge swing. The rider is attached to the main swing rope, so no problems there, the retrieval rope is the one that brings them back up to the platform. Depending upon load (test 40Kg or up to 180Kg with 2 riders attached) the rope comes back at different angles in relation to the crane boom.

This is the problem, we want to detect the end of rope about 2 meters before it hits the crane boom and prevent any further retrieval of the rope.

Hi Warren,

Firstly, Cabe has a solution of using an Optical encoder attached to a pinch-roller through which the wire rope passes at the winch-end.

Much better, attach a 6 inch diameter ball to the steel wire rope (with the wire rope passing through the ball) beyond the pulley but 2 metres before the hook. A well positioned laser sensor at the tip of the boom will detect precisely the ball as it nears the pulley.

Hope this meets your safety requirements.

Thomas

You can use both system, RFID and optical.

In the market there are many industrial RFID reader with different technologies, they can be connected to PLC or others embedded system.

There are UHF readers able to detect the Tag in a range of 4-6 meters, and you can set the output power of the reader in real time.

So, controlling the power, you can adjust the reading range of the reader.

Alberto S.

Thanks for your clarification. Seem like tere are some excellent ideas already put forth.

Considering that people are being carried, a redundant failsafe system would probably be best.

Perhaps primary would be a mechanical switch, activated by a fixed magnet or "stopper" on the rope itself. The stopper could pass through an eyelet assembly that not only gently guides the rope to the pulley, but guides the stopper onto the switch.

The RFID system could be a backup, but depending on where you are using it, interference and intermodulation (stray signals) could possible start or stop early.

Anxious to hear how the project turns out!

Hi Dave,

The main wiegt of the people riding is actually held by the swing rope. I have attached an image of the boom and ropes to give you some idea. It is great to have someone to bounce ideas off, thanks all for the input.

The rope position on the horizontal roller at the end of the boom can wander a bit too!

Attachments: