Software reviewed: Ch Mechanism Toolkit, Version 1.0
Company: Softintegration, Inc.
http:// www.softintegration.com
Price of the toolkit: $899 for
commercial, $199 for academic use
The Ch Mechanism Toolkit is a set of
high-level object-oriented
classes, callable from Ch or C/C++ existing programs, for the kinematic and
dynamic analysis of widely used closed-loop planar linkages and kinematic
synthesis of standard cams.
Ch is a C compatible multi-platform
scripting language which includes salient features from C++ and other
languages. Windows, Unix, and Macintosh
installations of Ch can be freely downloaded from the Softintegration,
Inc. website www.softintegration.com. Mechanical engineers with a traditional
background as Fortran programmers (as myself) will
easily adapt to
In particular, the Mechanism Toolkit
offers ready-to-use procedures for the following tasks:
- Kinematic
and dynamic analysis of four-bar linkages;
- Kinematic
and dynamic analysis of slider-cranks;
- Kinematic
analysis of five-bar linkages;
- Kinematic
analysis of Watt and Stephenson linkages;
- Kinematic
synthesis of four-bar linkages, but limited to a function generator
four-bar for 3 prescribed finite positions;
- Synthesis
of rise-dwell-return cams for different shapes of followers (i.e.
flat-faced or roller), of follower motion (i.e. translating or
oscillating).
There is even a procedure for the
generation of CNC code required for actual cam manufacturing. It is auspicable a wider choice of built-in
follower motion laws, now limited to harmonic and cycloidal.
All
the analysis procedures are based on closed form solutions. Thus, convergence problems are avoided since
no iterative solutions are involved and the analysis can be executed for
different assembly configurations of the linkage.
The Toolkit allows the user to quickly plot relevant computed quantities (e.g.
positions, velocities, accelerations, reaction forces, coupler paths,
transmission angles, etc.) by means of a single statement.
The
Ch Mechanism Toolkit contains the source code of its classes. Main theoretical
bases and detailed explanations of all the classes of the Toolkit are in the almost
500 pages Mechanism Toolkit user’s manual.
However, if the user has some knowledge of kinematics and a little of
experience of Ch programming, then the use of the procedures is best learned
directly from examples. Softintegration
maintains in its web site an updated FAQ section and publishes the answers to
various technical questions from the users.
A noteworthy feature of Ch and of
its Mechanism Toolkit is the possibility to run the code through the web. In fact, one can write a Ch code and manage
input and output of data through a web page.
The Softintegration web site gives several examples of this capability
which I do consider quite useful. For
instance, one can share with other users a computer program without the need to
release the source. Moreover, since the
program is executed directly on the server, it avoids the installation and
maintenance on different computers.
This last capability appears meaningful for members of a team sharing Ch
programs.
The availability in the Ch language
of a ready-to-use numerical library and the
possibility, within its Mechanism
Toolkit, to quickly generate animations makes this Toolkit an ideal development
tool for the early phases of mechanism design.
A set of graphical primitives (See Figure1) can
be used to visualize the motion of the planar mechanism under investigation.
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Figure 1: General and mechanical primitives available
For
these reasons the Ch programming language and the Mechanism Toolkit are strongly
recommended to those involved in the teaching, development and use of
mathematical procedures for mechanism design and analysis.
The workflow for obtaining mechanism
animations is depicted in Figure 1. Through the execution of the Ch program (program.ch) one generates a text file (file.qnm).
Then, this is piped to an ad hoc
application (Qanimate.exe) available in the Mechanism Toolkit. The result is a screen animation of the
mechanism. The user has the possibility
to cycle the animation, go step-by-step and adjust the speed. All are text files.
Figure2 Workflow for mechanism
animation
To illustrate the animation capabilities
of the Mechanism Toolkit, a Ch program (available upon request) for the kinematic
synthesis of a four-bar linkage for rigid-dody guidance has been
developed. The unknowns are the link lengths of a
four-bar linkage whose coupler moves a body through 3 design positions. A text file to be used for the computer
animation of the computed solution is generated through the execution of a Ch
program. The animation is needed to
test the absence of branch or order defects from the computed solution. Figure 3 is a screen snapshot of such
animation.
Fig.3 Rigid-body guidance four-bar
linkage
The Ch language offers many toolkits
and can satisfy different and specialized programming needs. Since Ch programs can be launched from a DOS
windows, no sophisticated hardware is required. The execution of kinematic synthesis programs
and mechanism animations are fast enough, even on old PC equipped with 400 Mhz
CPU. Finally, for Ch code editing and
execution I recommend the Crimson Editor (freeware available from
www.nullsoft.com) which can be customized for Ch sintax highlighting.
Reviewer:
Ettore Pennestri’
Professor
University of Rome Tor Vergata –
Italy
e-mail:pennestri@mec.uniroma2.it
Tel. : +39-0672597138