Design Overview ...
Design Objectives
Innovative Sports Training, Inc. has developed a motion capture product
which allows researchers to put more of their dollars into research and less
into efforts which contribute little to science. Our goal has been to ensure
that configuring equipment, writing software and manipulating data are not
the focus of the research effort. At the same time, we have retained the
flexibility which researchers have with "home grown" systems. The
MotionMonitor™ is a system designed by researchers for
research.
Total Solution
The MotionMonitor™ is a complete turn-key solution
including trackers for collection of kinematic data using a variety of
technologies; A/D data collection module for collection of EMG signals,
forceplates and other load cells; integrated video capture; event markers;
and, computer with peripherals.
Kinematic trackers include magnetic trackers by Ascension and Polhemus and
optical trackers by NDI's Optotrak. EMG systems include Noraxan, Delsys, Run
Technologies and Bortec. Forceplates include Bertec, AMTI, and Kistler. As
a result you enjoy a total solution. You don’t have to worry about or decide
whether you should be using an RS232, RS485, ISA or Ethernet interface for
the system as you currently contemplate it. You don’t have to wonder if your
choice will work if your system is expanded at a later date. You don’t have
to worry about collecting data from multiple sources and the problems of
synchronizing multiple data sources. The MotionMonitor™
has been designed as an integrated system that is seamlessly expandable from
our lowest-end system to our top-end system.
Hardware configuration and data selection are controlled with simple point
and click software menus which are intuitive in presentation and supported
with a Web based help manual. On-site installation and training ensure that
you can begin collecting data on day one. The manual contains examples and
videos together with technical explanations of key processing steps and is
backed up with unlimited technical support.
Sensor Assignment and Calibration
Our process of assigning sensors to each of 18 body segments is simple,
flexible and intuitive and can be accomplished in about five minutes. The
researcher can assign any number of the kinematic trackers to any, or all,
of the body segments. Sensors can be attached to any part of the segment.
During setup of the sensors, you will locate segment endpoints by means of
anatomical landmarks or joint centers by means of a centroid or rotation
processes. And now sensors can be attached to and track individual bones of
the hands, feet and spine.
Data Capture and Playback of Activities
Data capture is commenced with a mouse click and continues until the
user-established trigger is activated. The trigger is established by the
user and can be a keystroke or switch condition. AutoSave and AutoName
functions can be invoked to permit the capture and save process to occur
without user intervention. Upon completion, the activity can be immediately
replayed with a computer rendered image displayed in one window while user
selected data is displayed and graphed in other windows. If included in your
configuration, the Integrated Video Option can display a video playback in
another window.
Alternatively, the user can capture and view the activity interactively. In
this mode, the computer image of the subject appears on the screen and moves
in concert with the subject. User selected data is computed interactively
and displayed in real time.
Data Reporting
Data options are extensive. Raw kinematic tracker data and external A/D data
can be smoothed using butterworth filters with user selected cutoff
frequencies. Alternatively, bandpass filtering can be done in the frequency
domain. Segment end points and centers of mass can be examined
for position, displacement, velocity and acceleration as well as
orientation. Orientation angles, including their velocity and acceleration,
can be reported as Euler angles using any rotation sequence, rotation
matrices, quaternions, Grood-Suntay angles, helical axes or segment angles.
Orthopedic angles for all of the body joints may also be selected for
computation and graphing. Joint forces and moments can be calculated using
either a top-down or a bottom up linked segment model. All data can be
computed in either the time or frequency domain relative to any base
reference frame. Data generated from drop down menus can be employed
in user-defined equations that follow standard mathematical conventions are
also available for immediate viewing.
Data can be selected in any combination and plotted real-time together with
a 3-D rendered image that may be rotated or zoomed in and out. Alternatively
the data may be exported to an ASCII file for processing and analysis in
other software. Numerous standard report menus and macros are available for
presenting data that has been exported to Excel.
Measurement Space Coordinate System
The measurement space coordinate system is totally within your control. You
can accept the default or specify its origin and orientation at startup in a
simple three-step process. And you can change it at any time. This
capability becomes critical for example, when you try to relate center of
pressure readings from a forceplate to the measurement space. With
The MotionMonitor ™, forceplates are calibrated with center
of pressure and force vectors reported in the same coordinate system as the
kinematic system.
Measurement Rates
Measurement rates can vary for each type of equipment being monitored. The
measurement rate for kinematic trackers is a function of the type of tracker
being used. Magnetic trackers can be set at any measurement rate from 30 to
144 Hz for each sensor. Optical trackers can monitor body segments
at speeds up to 1,000 Hz divided by the number of segments to be tracked.
Forceplate data can be monitored up rates up to 25 Khz with EMG up to 150
Khz divided by the number of channels being collected.
Regardless of the measurement rate selected, The MotionMonitor ™
software will automatically synchronize data from all of the
sources.
Accuracy and Resolution
Accuracy and resolution varies by the type of kinematic tracker incorporated
into the system. Northern Digital's Optotrak has an RMS postional accuracy
of 0.1 mm in the x,y coordinates and 0.15 mm in the z coordinates with a
resolution of 0.01 mm at 2.5 meters. Ascension Technology's magnetic
sensors have an RMS position accuracy of 0.07 inches/0.5 degrees at a 36
inch range with a resolution of .03 inch/0.1 degrees. With an extended
range transmitter, position accuracy is 0.3 inches/0.5 degrees at a
five-foot range and 0.6 inches/1.0 degrees at a ten-foot range with
resolutions of 0.03 inch/0.1 degrees at five feet and 0.1 inch/0.2 degrees
at ten feet. Alternative technologies involve trade-offs in addition to
accuracy and resolution including up front cost, on-going operational cost,
ease of use and the like. Technical support personnel work with the client
to ensure that the hardware selections are appropriate for their budget and
research requirements.
Large metal objects in the measurement space can distort readings on
magnetic trackers. Innovative Sports Training, Inc. has developed a system
for dealing with metallic distortion which allows for a much more flexible
measurement space. With The MotionMonitor ™ a
"mapping" procedure generates correction polynomials so that metallic
objects such as treadmills, etc can be introduced into the measurement
space. When your system is installed, you will receive an analysis of just
how accurate your system is and the RMS error associated with position and
orientation readings. And each time you start your system, you will receive
a warning if the measurement space has been distorted by the introduction of
unexpected distorting elements.
A/D Data Collection
Synchronization is a major issue when multiple data sources are collected.
Published studies have shown that a single frame error between kinematic and
kinetic data can produce errors of 20% in hip moments. With The
MotionMonitor™, the easiest approach is to collect all analog
data, e.g. forceplates, EMG etc., directly to our system. All data is stored
together and is perfectly aligned and easily accessible by The
MotionMonitor™ software. We refer to this as "integrated" A/D
to distinguish it from data which is merely synchronized. The benefit of
"integrated" A/D data is the ability to use it in real time calculations.
Thus for example, it is possible to generate real time output or create
bio-feedback capabilities which incorporate not only kinematic data but also
kinetic and EMG. A convenient BNC interface panel is available for
connecting EMG and forceplate leads.
We also provide up to 16 external event markers (e.g., heal strike, audio
signal etc.) which can be used to mark data files for the occurrence of
events of interest.
If you must collect data in an external system, The MotionMonitor™
can generate either a timing pulse to trigger the collection on the external
system or a synchronization pulse to mark both The MotionMonitor
™ and external files for later synchronization.
Customizing Software & Collection Procedures
Each user can setup his/her preference file to control the flow of software
for their unique requirements. For example, during the design of an
experiment or analysis following capture of an activity, the user may want
to exercise a great deal of control between each capture and playback and
review data in a free-form fashion. Once the experiment has been designed
and during actual data collection, the researcher may want to automate the
collection and storage of files so that activities can be captured with
little or no interaction by the researcher. For example, the researcher may
want to trigger the completion and storage of the activity upon the
occurrence of an event marker such as a heal strike or when the subject
touches an object, etc. Each of these is accomplished with a simple mouse
click with The MotionMonitor ™.
System Expansion
The system has been designed to ensure a seamless expansion as your needs
change. One can start with a simple two or three tracker system and add more
kinematic trackers tomorrow. When forceplate or EMG data is required, add
the A/D module. An integrated video option can also be added at any time.
Last Updated
11/1/2003
