Measuring speed moving object with device connected to PC

I want to measure the speed of a moving object with an external device attached to a Windows PC. We have several machines for which we need to measure the speed of a moving part. This part is moving from 0.5 mm/min to 3 mm/min (Minute).
I am thinking of a device which can measure height with high accuracy 0.01 mm or less for a range from 10 cm to 100 cm. This device has to be connected to a Windows PC with USB or RS232. With drivers for Visual Basic.

Has anybody experience with this?

You could use a micro plc and an array of sensors for detection and speed measurement, this would allow RS232 or Ethernet options.

Another option is a vision system, they are capable of measuring height, width, length, area, volume, size, position, number of objects, positioning and more.
http://www.sick.com/home/factory/catalogues/industrial/machine_vision/en.html
These can be directly connected to a computer thru RS232/485 or Ethernet.

what is moving part? can measuring devicebe connected to it?

(i hope it'snot hot cookie or blob of jelly).

For PC interface, you could use any DAQ like NI USB9215A.
it comes with drivers for VB6 and VB.NET for example.

If (and i'm guessing here) the application requires non contact measurement with high accuracy, you may want to check into a laser doppler or laser displacement type sensor. You will need to know the size and direction of the target, and the total length of the motion to be measured. These devices have a limited sensing range at that level of precision. I have used a Canon laser doppler velocimeter for non contact speed measurement. Extremely expensive. Terrible customer support. It puts out quadrature encoder pulses and is accurate to 0.01mm. I bet there are other brands of similar devices.

RANT: Some one needs to build a senor with the same technology that's in my optical mouse for just such applications. I can buy one of those for $20, but the industrial equivalent is $6000.?!?!

Without more details, it would be hard to suggest a good sensor. Can you attach a sensor to the part? Is it held captive by part of the machine or free falling from a hopper? Give us more info please ...

Paul C.

Additional infomation

The moving part is a kind of arm moving up and down with low speed. Measuring devices can be connected.
We want to check the speed periodically (once a month or so) from each machine with an external device (We want to use the same device for all machines).

How about a string pot with a magnetic base?

String Pot

LVDT (Linear Variable Differential Transformer) with a signal conditioner