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How to skin a Cat(scanner), or Happy Dentist, Healthy Smile!

So, as many of you heard this morning, I made an emergency dentist visit. His cat scanner sounded like it had a cat wrapped up in the gears. Here's what I found.

I used my cellphone for the pictures, so it didn't catch the top. But, you will see the top, cover off, in the later pictures. the big part in the middle of the picture is called the Gantry.

Here's the operator control panel.

Here's the top of the machine, uncovered. The most prominent part of the first picture is called the Gantry. It has the Xray source on one side, and the solid state detector on the other. You see two lead screws above. They position the gantry properly around the patient. The round steel disk is attached to the gantry support axis. A stepping motor drives this plate to rotate the gantry around the patient.

Here's a close up of the Gantry Rotate servo. The stepping motor is off to the left. You can see the steel wheel that drives the disk to rotate the gantry. The screw with the spring adjusts the force the wheel applies to the disk. This force determines the amount of drive friction, and therefore breakaway force. If the patient moves during the scan, this drive is meant to slip so as not to harm the patient.

Here is the other side of the servo. To the right is the motor driver board. Top center is the opto isolators. They look for the "Flags", that tab held down with 2 screws, and it's compliment behind the wires. They signal "End of Travel" to the computer. So, here's the problem. The machine is powered up and does a calibration. During the process, it spins the gantry all the way to one end stop. It then knows that it takes a certain number of steps to get to the other end stop. Issue those steps and see the stop, All is well! Issue the steps and no end stop, STOP!!! ERROR!!! Turns out, there was a substantial layer of dust and dirt on the gantry drive wheel and disk. The wheel would slip and make a racket, resulting in an error. As you can see, it's all nice and clean now. Computer, Dentist, Practice Manager, ALL happy now!!! Back in business. I'm sure this would have been an expensive service call! The good news, it looks like a dental cat scanner is a lot smaller and easier to repair than the full body scanners I serviced in the past 😀

So, now you know why I never know what the day is going to bring. Retirement is interesting, busy and Fun!


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