I am currently doing one project about Mobile Robot Teleoperation, so stream video over network is one of my part. Actually there are many different approaches, but I chose OpenCV as my main approach because of its advantages in term of Computer Vision. But the crazy thing I have to do is making 2 server and client programs which run in Windows and Linux, respectively. Ok, now let’s go together:

Install OpenCV

OpenCV (Open Source Computer Vision) is a library of programming functions for real time computer vision.

• OpenCV is released under a BSD license, it is free for both academic and commercial use.
• The library has >500 optimized algorithms (see figure below). It is used around the world, has >2M downloads and >40K people in the user group. Uses range from interactive art, to mine inspection, stitching maps on the web on through advanced robotics.

For more information, go to OpenCV Wiki. It is not difficult to build OpenCV in Linux, just base on Install Guide but make sure that install all Prerequisites: Python, Intel TBB, …

In Windows counterpart, I can easily build OpenCV using Microsoft Studio, but I am using program which has multi-thread (POSIX) feature, so I can’t use this library for that. So I prefer to build OpenCV using Cygwin, but I didn’t get success yet :d. So what I have done with that ?

• Download OpenCV-2.1.0-win32-vs2008.exe and install it
• Download OpenCV libs compiled by Cygwin and put it to the /bin and /lib from Python OpenCV project. Just download opencv210_mingw.7z

And don’t forget to install Cygwin and needed packages like gcc, make, cmake, … before that

Program

This post describes very well about what do you have to do with OpenCV and socket programming. Thank Nashruddin for great effort. But I would like to contribute some things here: cmake list and delay function.

I really love Cmake so much, it is very handy and powerful tool for cross platform applications. If you don’t know what is Cmake, have a look at http://cmake.org/, you will love it for sure.

In the folder which has your source code, just create a file named CMakeLists.txt. For the server part it will be:

project(MobileApp)
cmake_minimum_required(VERSION 2.6)
# Find OpenCV package
FIND_PACKAGE(OpenCV REQUIRED)
# Vision program
add_executable(stream_server stream_server.c)
target_link_libraries(stream_server ${OpenCV_LIBS})

REQUIRED
For the client counterpart:

project(MobileApp)
cmake_minimum_required(VERSION 2.6)
# Find OpenCV package
FIND_PACKAGE(OpenCV REQUIRED)
# Vision program
add_executable(stream_client stream_client.c)
target_link_libraries(stream_client ${OpenCV_LIBS})

To build the application, follow these steps:

$ mkdir build
$ cd build
$ cmake ..
$ make

cmake will automatically generate your Makefile based on your system configuration, so whenever you move it to other computer or other platform it will check again.

Note: there is one issue that cmake couldn’t understand the parameter OpenCV_LIBS even thought it can detect OpenCV libs, so you need to add OpenCV libs by using other variable OpenCV_DIR.So you need to change ${OpenCV_LIBS} to ${OpenCV_DIR}/libs. Have a look at FindOpenCV.cmake

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This post, I would like to introduce about the HapticMaster just like a summary about the paper I have read: The HapticMaster, a new high-performance haptic interface

What is the HapticMASTER ?

As you can see from the above picture, the HapticMASTER is a 3 DOF device designed by FCS company and there are 2 dedicated industrial computers for a inner controller and a outer controller. Both of them use VxWorks real-time operating system.

The end effector plate workspace of the HapticMaster spans a 3-dimensional space with a volume of approximately 80 liters. The end plate of the robot arm allows the mounting of difference end effectors.

Controller of HapticMASTER

The HapticMASTER is a force controlled haptic interface:

• Input: force from the human
• Output: the proper displacement

It means when a human pushes the hand, by using the force sensor the device can measure an exact force, therefore give the proper displacement. So simply called: force in and displacement out. It is a Admittance control.

There are 2 controller which are inner servo loop and outer control loop. I just take an explanation from the paper:

The HapticMaster measures the force exerted by the user, preferably measured close to the human hand with a sensitive force sensor. An internal model then calculates the Position, Velocity, and Acceleration (PVA), which a (virtual) object touched in space would get as a result of this force. The PVA-vector is commanded to the robot, which then makes the movement by means of a conventional control law. The general control algorithm is illustrated in Fig. 2. The internal model will typically contain a certain mass, to avoid commanding infinite accelerations. The inner servo loop will cancel the real mass and friction of the mechanical device.

An other interesting thing is two loops of the controllers run at a fixed update rate of 2500 Hz, which is approximately ten times higher than the maximal human discrepance value [Burdea, 1996].

There are some examples people in some laboratories did with HapticMaster:

Click here to view the embedded video.

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