How I Developed a Crib Swing Device

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This article is about how I developed a device for swinging a crib with a pendulum mechanism.
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This story began more than three years ago, when my wife and I were preparing for the birth of a son. Among other things, I attended to the purchase of a crib, began to research the market on this topic. It turned out that today the following types of cots are sold:
  • Just a crib, standing on its feet. The legs are usually equipped with wheels.
  • Rocking cot with an arcuate snake.
  • Crib with a pendulum swing mechanism.

Pendulum mechanisms are longitudinal (the cot sways along the long side, as in the title picture), transverse (the cot sways along the short side) or universal. In the latter case, the same crib can be assembled both ways.

There are still cradles - a small cradle, which is convenient to put next to you when you are doing something, and the baby is awake.

There are still playpens, Chinese. There are also transforming beds, a chest of drawers and a changing table are attached to them from the end, and there are also options with a pendulum. And there is much more that is exotic.

But I was specifically tuned for a traditional bed, standard sizes, made of birch or beech, with a pendulum swing mechanism. Well, as a “progressive, advanced person,” I immediately thought that I couldn’t swing this crib with my hands. Surely, I thought, rocking mechanisms have long been invented, you just have to go to the store and buy.

However, to my surprise, it turned out that there was no finished device on sale. But there are tips. For example, tie the rope with one end to the foot, and the other to the bed, and shaking the leg, swing the bed. You can even sit at the computer. Or you can tie the rope to the table of the CD-ROM, and write a program that will open and close the table with some frequency. And you can use the drive wipers from the old "Lada". And so as not to make noise, place it in the next room, and draw the rope from this room to the nursery through a system of holes, pulleys and blocks. There are tips even more radical - do not download at all. Because, probably, it is harmful and in general, in Sparta, for example, they did not shake the children, and everyone was happy with everything.

In addition to the tips, several patents were discovered, but no devices were made on them. There was one seemingly manufacturer, I would even buy, probably, then their device. But at that time it was already impossible - as I understand it, they turned production, if it was.

So it occurred to me to develop my own device for rocking the crib.

I analyzed all the patents and other materials found on the Internet that could help me. I also had to disassemble the children's Chinese electric swing to see what was inside.

The requirements for the device gradually formed:
  • Noiselessness. This means that there should be no motors, gears, gearboxes. You can, of course, make soundproofing, but it is better to do without all this initially.
  • Possibility of remote control. And this, in turn, means the ability of the device to swing the crib from a state of rest.
  • Easy crib installation. And, as a result, the possibility of installing, if not all, then at least most of the beds available on the market.

Thinking about the design of the device, I noted for myself several key points. Firstly, the rocking device must adapt to the frequency of the natural oscillations of the crib, pushing it at well-defined, necessary points in time, just as a person standing on the ground swings the swing. In addition, the connection between the crib and the drive should not be rigid, it is necessary to make sure that the swinging bed can be stopped at any time by hand without damage to the drive and hand. The crib should swing itself, and the drive will only compensate for the energy dissipated as a result of friction. This in turn will determine the low power consumed by the device.

Remember, desktop perpetual motion machines were popular at one time? There is a coil in the stand, and a magnet in the swinging part. It is enough to swing the “engine”, and it will swing until the batteries are sitting in it.

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The principle of operation of the device is simple - a magnet flying over the coil induces an EMF in it, which changes sign at the moment when the magnet begins to move away from the coil. Here on the same principle, I decided to create my device. An important point - I decided to use the same drive coil as a sensor (and not, for example, another coil, optocoupler or Hall sensor). In other words, the microcontroller (and the design is built, of course, on it) first "listens" to the EMF in the coil, and then at the right time connects the same coil to the power source.

Walking from an idea to a finished device, I had to solve many questions. ATtiny24 came up as a microcontroller. The magnet was chosen neodymium, in the form of a washer, with a diameter of 15 mm and a thickness of 8 mm. A separate story with a coil - its parameters had to be carefully chosen using both a theory and several prototype coils with different sizes, wire diameters and number of turns. The geometry and materials of the core also varied. Of course, I wanted to make the magnetic system as closed as possible, ideally the magnet should move with minimal gaps between the poles of the core. In this case, the highest efficiency of the device (and, therefore, the minimum amount of copper in the winding) would be achieved. However, for the sake of simplicity of the design, high efficiency had to be sacrificed.

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In order for the swing mechanism to move the crib from place, a certain displacement of the coil relative to the magnet in the equilibrium position was provided.

Remote control was performed using a ready-made Chinese remote control with four buttons (start, stop, more, less) and a receiver for it. Now we are using such a remote control:

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In the program for the microcontroller, six rocking speeds were provided (essentially, the length of the boost pulse changes). For the sixth speed, the algorithm is somewhat more complicated - it uses a series of short pulses with a check of the polarity of the induced emf in the pauses between them. This allows you to achieve maximum swing energy.

During these three years, as new ideas emerge, the program improves. For example, an algorithm has been tested (and is now being used) for dynamically changing the length of pulses depending on the period of the crib's swing. An algorithm has also been created for a smooth increase and smooth decrease in current in the drive coil, which determines the complete, absolute noiselessness of the device. Without this improvement, the device still made some sound like a ticking clock. There is also the idea of ​​creating a PI controller with feedback on the amplitude of the swing, but the problem of determining this amplitude with the help of the existing “sensor” has not yet been solved.

The finished Gainta case was chosen as the device case, after some time he got a beautiful picture engraved with a laser.

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The power supply is ready, 12 V, 2 A.

A few more photos of the device:

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Non-standard fasteners are cut using laser cutting and painted with powder paint.



And the video:



We used our rocking device for about a year, my wife was very pleased. And then the child refused to rock out in the crib, and the device turned out to be irrelevant for us.

And then it turned out that such devices can be sold. But that's another story.

If you like this article, I can tell you:
- about how I got a patent for a utility model, and how it turned out to be practically useless in a real case of a violation of my patent rights;
- about how I started mass-producing and selling rocking devices, but so far I haven’t gotten rich;
- about how the device has a new control panel with a screen from Nokia 1202, as well as additional functions.

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