Shaft Encoder with Pulleys/spring/spool

In summary, the speaker is trying to measure the instantaneous velocity of a swimmer at 400Hz using a setup involving a nylon rope, pulleys, a wheel with a shaft encoder, and a spool. They are facing difficulties in maintaining consistent tension in the rope, but have found that constant force springs and fishing reels may be helpful. They are considering using a baitcasting reel with a drag setting and possibly adding constant force springs to maintain tension. They plan to test the setup with a fishing reel and adjust as needed.
  • #1
elixirnova
12
0
Alright I am trying to measure the "instantaneous" velocity of a swimmer at around 400Hz.

I plan on attaching the swimmer to some nylon rope or something similar and having the rope go into a "box" that will use pulleys, a wheel mounted to a shaft and shaft encoder that will rotate freely between two bearings, and a spool that will feed the line.

My big problem is maintaining tension in the line that is fairly constant and negligible (probably 1lbf or less would be nice), but consistency is most important for testing.

I have found out there are constant force springs out there. So I figure I could attach a pulley to one of those to maintain tension on the line, but with constant tension on the line(which is needed) the line will always be unspooling from the spool faster than it needs to be...

The swimmer's velocity will fluctuate between around 3m/s and 0m/s at the most extreme situation and velocity fluctuations can be expected up to around 10Hz.

Any ideas on how I can make this work?

Here is what I have so far
Velocity_Measurement_System.jpg


Also, I tried looking up belt tensioners for car but couldn't find anything to show how they work. Could a belt tensioner help me?
 
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  • #2
Just searching around google, would a fishing reel work as my spooling mechanism? It has a reel already attached and perhaps the drag can be used to maintain tension and once the tension is achieved it let's out line and if too much tension persists to build up perhaps the constant force spring could be used to prevent excess tension while the line unspools from the fishing reel.

So maybe the combination of a fishing wheel w/drag and a constant force spring?

Edit:
So here is a reel that looks good. It seems like a baitcasting reel would be best and here is a cheap one I found http://www.kmart.com/shc/s/p_10151_...003a&ci_src=14110944&ci_sku=089V002609844000P

Not sure about the open faced and closed faced reels though. I suppose I ought to set up the measurement wheel/shaft and see how the fishing reel works in the device and I can always add constant force spring(s) to help keep the tension constant.

The only possible problem I can see is the fishing reel requiring too much tension or providing inconsistent tension with it's drag setting.
 
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1. What is a shaft encoder?

A shaft encoder is a device that converts the rotational movement of a shaft into digital signals. It typically consists of a rotating disc or wheel with evenly spaced slots, and a sensor that detects the movement of the slots and generates electrical pulses.

2. How does a shaft encoder work?

A shaft encoder works by using a light source, such as an LED, and a light sensor to detect the movement of the slots on the rotating disc. As the disc rotates, the light source is interrupted by the slots, and the light sensor detects these interruptions and converts them into electrical pulses. These pulses are then counted and translated into digital signals.

3. What are the different types of shaft encoders?

There are two main types of shaft encoders: incremental and absolute. Incremental shaft encoders generate pulses for each rotation of the shaft, while absolute shaft encoders provide a unique binary code for each position of the shaft. Other types include linear shaft encoders, which measure linear movement, and rotary shaft encoders, which measure rotary movement.

4. What are the applications of a shaft encoder?

Shaft encoders have a variety of applications, including in robotics, industrial automation, and motion control systems. They are commonly used to measure speed, position, and direction of rotation in machines and equipment. They are also used in consumer electronics, such as computer mice and gaming controllers.

5. How do pulleys, springs, and spools affect a shaft encoder?

Pulleys, springs, and spools are often used in combination with a shaft encoder to provide tension and stability to the rotating disc. The pulleys help to rotate the disc smoothly, while the springs and spools help to maintain the proper tension on the disc. These components are essential for accurate and reliable measurements from the shaft encoder.

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