First Welding Tests

Now, there is a time to test, if the generator is capable to heat the flexible vinyl foil significantly to weld it. The generator can be set easily. It can be started by external signal or internally, by the small arm on the probe top end. Operation stops in time set on the timer dial. For tuning, the mode is better to set as infinite, without time limit. Then, it is possible to start and stop generator manually and find the best output power using the tuning knob.

Before process.

Welded quite successfully.

Quite success, but overheat a little.

Finally, the maximal output power was found a quite big. The vinyl foil was welded in the time between 0.3 - 0.6 s. Sometimes, the heat was as high that the hole through was made. Sometimes, a gas was produced, which expanded and tore the weld apart. There is also problem with pointing accuracy, because due to ultrasonic vibration, there is very difficult to maintain the welded place, if the probe is hold by hands only.

The next research will be focused to more precise power setting, making better holder for accurate pointing and also it will be good to make another shape of the rod, where the energy will be distributed better.

Inside Generators

The electrical connection was inspected briefly and found pretty simple. There is no any integrated circuits inside, only simple power supply, oscillator and amplifier.

The front panel.

Timer dial in center, tuning knob and output power indicator on the left, then connectors for the probe and for the external triggering. On the right side, there are input and output power indicator lights, power switch and mode switches.

The rear panel.

Under the cover.

The probe.

The arm on the top end of the probe is equipped with a micro switch and can be used as an internal trigger.

The rod.

The rod can make spot about 6 mm in diameter. There are another rod shapes available at Honda Electronics, but we have this one only.

Artificial Japan Eectrical Network

Because of unique opportunity, I managed to obtain two old ultrasonic  generators from the scrap equipment of one local factory. Nobody knows what to do with them in comparison to many another useful devices they gave away, so the way to them was open. Now, the question is - could we use the generators for the flexible PVC material welding?

Connected transformers to produce a 96 V power.

At first, we need an electrical power. The generators was made by Honda Electronics and have power input for Japan network (maybe regulated), 100 V, 150 W. I don't have any regulation transformer and making stable transformer from 230 V to 100 V is expensive. So, I take four similar transformers to 24 V taken from four old VCRs I found in trash before many years. At the primary, I connected them in parallel to a 230 V. The secondary winding was then connected in series to get 96 V. When loaded to 150 W, there was no significant voltage drop. At last, the Japan outlet connector was added. I had it at my storage I don't know from.

Microcontroller Unit Software

The microcontroller unit acts as an universal device for several experiments and tasks. It is not possible to predict all the functions and features needed in future, so both, the hardware and also the software is modular. The software consists from HAL, the Hardware Abstraction Layer, which isolates all the internal and external peripherals from application, next is the UART Communication Module and the Application Module. Maybe, there will be more in future.

The Application Module contains calls for initialisation all the system and then it is branched into 16 application functions. The function is selected by the DIP switch combination, which is read once after system RESET. Every from the application functions have its own purpose, isolated from others.

Up to now, we have implemented these application functions:

00 - Hand Control Mode

In this mode, there is unlimited loop, when the air pressure is measured in the time interval given by TIME_MARK constant (usually 20 - 100 ms). Data are put on the UART interface in 4digit HEX format. Sending the message is indicated by the yellow LED flash.

When the ADC converter is saturated during measurement, the red LED will glow until another, not saturated value is get. This acts as a overload indicator.

Also the FET switches can be toggled, one button is used for the FET switch selection and second for selected FET switch toggling.

01 - Pressure Record Mode

After RESET and initialisation, the green (init ok) and yellow (waiting) LED glows. The program is waiting for the key press to start. When one of the buttons is pressed, the recording loop will begin.

In the loop, the air pressure is measured in the sampling frequency given by the TIME_MARK constant (usually 20 - 100 ms). When the actual sample is different than previous, result is sent onto UART, together with the time mark number. Message format is simple - two decimal long integers on the line, separated by comma character. Sending of the message is indicated by the yellow LED flash.

When the ADC converter is saturated during measurement, the red LED will glow until another, not saturated value is get. This acts as a overload indicator.

During the loop, both buttons can be used for FET output toggle - you can switch on and off the air compressor or draining valve.

Air Compressor and Valve test

At some experiments, we need a small, but reliable pressurized air source. As a simple solution, a 6 V DC air compressor was tested, taken from a personal blood pressure meter.

The small air compressor from personal blood pressure meter

The DC motor is marked as WRF-370C-22170 and the air pump KPM27C-6C2. Its disadvantage is the air leakage through the compressor, when it is stopped. So there is impossible to make a stable air pressure with it.

Small electromagnetic 3-way valve coil needs 24V / 40mA

We attempted to get rid of the air leakage using electromagnetic valve added after the compressor, but this also was not successful. The leakage was smaller but it was not cancelled.

In the video the air pressure source is used to operate a piston actuator from an old medical machine. The pressurized air source works, but use it for measurement purposes is impossible.

First Measurements on Toys

We are ready to first real test of the air pressure measurement in the vinyl inflatable toy. The first question is, how big is the air pressure in the toy when it is loaded by human body. Next, we are curious, if the pressure is bigger in larger or in smaller air chamber, when the load is the same. Also, we would like to know how big is this difference.

The toy inflation

So next, we inflated a nice INTEX black whale toy and connected it's air valves to our new pressure sensor. The sensor was connected using old air mattress pump nozzle and aquarium 4 x 1 mm hose approximately 2 m long. We believe, that this will not make any significant distortion of pressure changes.

The pressure sensor connection

The pressure was measured in both air chambers, in the large body and in the smaller tail. At beginning, the air pressure was near the same which was given by the air pump used. Next. both chambers were loaded by human body weight and then released several times. All air pressure changes were recorded.

The air pressure in the body recorded

The air pressure in the tail recorded

One can see that the air pressure in the tail can achieve bigger levels, approximately 6.5 kPa peak in our experiment. In comparison, the body achieves only near 3.5 kPa. Also, note the negative peak when the chamber was released, more visible at big body air chamber. Time mark in both charts was set to 20 ms.

Pressure Sensor Calibration

We have all equipment ready, so we go to calibrate the pressure sensor. The U-tube manometer and the electronic pressure sensor were connected together and the air pressure source was added to.

The U-tube reference manometer setup

In the first concept, the small 6V electric compressor from a personal blood pressure meter would be used as a pressure source. But, there was strong problem with the air leakage when the compressor stops. This was not solved by using any of electromagnetic valves after the compressor.

The piston actuator as a reference pressure source

Finally, the piston actuator from old medical machine was used as a very reliable pressure source and it gave exactly the range we need for sensor calibration. There was no leakage in this setup, so if we set the pressure value by the piston move, it will remain without any further change.

A little strange, but reliable connection to U-tube

Water columns balanced in the U-tube

Water columns unbalanced in the U-tube

Finally, we take several values of the pressure represented as a water column heigh difference in the pipes and as the counts value from the electronic sensor. Data from the U-tube manometer were converted into kPa and arranged in the table along with data from the sensor. Then the data was fitted by line and its constants were obtained.

Then, constants were implemented into microcontroller in the main unit. We can measure the air pressure in Pa directly now. Constants was implemented in long integer multiplied by 1000.