您可以减慢USB总线的速度吗？

Question

I want to build a webcam based 3D scanner, since I'm going to use a lot of webcams I doing tests before.

I have orderer 3 exact camera that I will drive in python to take snapshot at the same time.

Obviously the bus is going to be saturated when there will be 50 of them. What I want to know is if the camera are able to hold the picture until they are transfered to the computer.

To simulate this behavior I'd like to slow down the USB bus and make a snapshot with 3 camera, I'm under windows 7 pro, is this possible?

Thanks.

PS : couldn't I saturate the USB BUS by pluggin some USB external harddrive and doing some file transfert?

Answer 1

What I want to know is if the camera are able to hold the picture until they are transfered to the computer.

That depends on the camera model, but since you mention in your post you are using "webcams", then the answer is almost certainly no . You could slow down the requests you make to the camera to take a picture though.

This sequence of events is possible:

1. wait
2. request camera takes picture
3. camera returns picture as normal
4. wait

This sequence of events is not possible (with webcams at least)

1. wait
2. request camera takes picture
3. wait
4. camera returns picture at a significantly later time that you want to have control over
5. wait

If you need the functionality displayed in the last sequence I provide (a controllable time between capture and readout of the picture) you will need to upgrade to a better camera, such as a machine vision camera. These cameras usually cost considerably more than webcams and are unlikely to interface over USB (though you might find some that do).

You might be able to find some other solution to your problem (for instance what happens if you request 50 photos from 50 cameras nd saturate the USB bus? Do the webcams you have buffer the data well enough so that it achieves your ultimate goal, or does this affect the quality of the picture?)