Gyroscope Benefits

Human skeletal components are connected through hinged joints which permit rotational motion about the joint. The gyroscope is the only sensor that can directly measure that rotation.

Traditional gyroscopes are rather large and contain rapidly spinning masses which actually exert a gyroscopic force on the object which they measuring. Both their size and interaction forces make them unsuitable for mounting on the human body, particularly at the extremities where they would greatly influence the motion of the hand, foot, etc.

Why Motus?

The new and unique Motus gyroscope is a miniature sensor that contains a micro machined quartz tuning fork and 6,400 solid state electronic components. It operates on the Coriolis principle and measures true inertial angular rate. Its influence on what is being measured is negligible since it is small and contains no rotating parts.

Earth's gravity does not affect the Motus gyroscope, but directly affects accelerometers which are typically designed to sense Earth's gravitational acceleration. The gravity insensitive feature of the Motus gyroscope greatly simplifies test protocols. For example, using it, one can measure a hand tremor with the arm/hand held vertically or in a horizontal plane, yielding the same clear tremor measurement. The Motus gyroscope makes most tests possible where they were previously thought to be impossible.

Ease of Use

A Motus gyroscope (sometimes termed an angular rate sensor) is easy to use, requires little training and can eliminate the need for multi-camera photographic systems with their attendant need for complicated analyses and coordinate transformations. Unlike the camera systems, the Motus system is portable and can be easily taken to various other clinics, even into the patient's home.

Highly Sensitive Measurements

Movement at the very low frequencies typically found in human motion can be measured by the Motus system which will measure down to DC or zero hertz. It also measures frequencies up to 70 hertz, typically far above those found in human movement. The Motus system then filters them so that the response is flat to 30 hertz and displays the data from 0 to 20 hertz on the monitor. Note that other sensors often do not have a DC capability.

The location of the Motus gyroscope is uncritical in certain types of tests on rotating limbs since there is no response to "tilting" as seen in accelerometer use. Furthermore, since the gyroscope measures true inertial angular rate it can, for example, be placed at either end or in the middle of a lower leg and achieve identically correct results.

Greater Accuracy

Since the gyroscope measures angular rate in degrees per second, a simple integration will yield angular position. Accelerometers require two integrations to get position and can easily introduce significant errors in the double integration computation due not only to sensor drift but also to the mixing of Earth's gravity signals with the desired human motion signals.

Long Term Stability

The Motus gyroscope uses a single crystal quartz element as its key component, thus benefiting from the long term stability of quartz. This design feature results in excellent long term stability of calibration, eliminating the need for periodic recalibration and yielding highly repeatable measurements of rotational motion.