On the design of an experimental installation to determine the kinematic parameters during human locomotion.

Rosca, Ileana ; Radu, Ciprian

1. INTRODUCTION

The design of external prosthetic elements of locomotor system involves previously some complex kinematic and dynamic studies of the interested anatomical system.

Kinematics is part of mechanics concerned with the description of movement. The kinematics description of movement encompasses positions and angular positions of body segments. To determine these unknowns there are o lot of methods, such as: exoskeletal method, accelerometry method and stereometric method (Medved, 2001).

The stereometric method is the largest and the most diverse group used to determine the kinematic parameters of human movement. This measuring method may be classified in several ways. This classification includes: close range analytical photogrammetry fundamentals method and the high-speed photography method. The last method is the most used that because is the simplest and the less affected by errors method. Besides attaining a very high spatial resolution and accuracy of less then 1%, the basic quality of the photographic method is its non-invasiveness, not disturbing the subject and no expensive costs (Vaughan et al., 1999).

A further, important comparative advantage of this method is the permanent storage of the complete photographic record of the movement structure recorded. This offers a rich informational background during analysis, as well as a possibility to redefine characteristic body points in later analysis. This is further suitable for combined qualitative and quantitative analysis (Vaughan et al, 1999).

2. EXPERIMENTAL DESIGN SOLUTION

2.1 Experimental objectives

The experimental objectives consist in determining of kinematic parameters of lower right limb, more exactly the angles between anatomical segments during locomotion. These angles are represented by: the angle between thigh and shank ([alpha] angle), the angle between and shank and posterior side of foot ([beta] angle), the angle between shank and frontal side of leg ([delta] angle) and the angle between foot and ground ([phi] angle), during stance phases of normal locomotion (see figure 1).

Also, for a complete biomechanical analyze we have decided to determine the trajectories of lower limb's joints during normal locomotion.

2.2 Measuring method

Biped human locomotion is a phenomenon that progresses in real time, so it's necessary to choose a right method to be concluding in this way. Since we try to analyze qualitatively some continuously and successive positions of lower limb's joints during normal locomotion, it's necessary a high precision visual analyze.

Once, human eye is perceptible for a distinct number of 24 different frames per second (for 24 frames per second the images will be in continuously movement), it's necessary that the tracking to be made to a high speed frequency that is comparable with locomotion speed and then to bring it close to the normal observation frequency of human eye (Hunt & Lataman, 2006).

Considering these, we have chosen the high-speed photography method, which consists in continuously video recording of the human subjects during normal locomotion (4.5/5.6 km/h), followed afterwards by image discrete quantity, which succeed in 1/250 frames per second.

The discrete frames can be edited using image edit software, finally to obtain the successive positions of the markers, which are positioned in the lower limb's joints (hip, knee and ankle joints), heel and the second metatarsal's pick.

2.3 Experimental installation description

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

To determine the kinematic parameters of human normal movement is necessary to design an experimental installation. The proposed experimental installation, presented in figure 1, is compound from: a high speed video camera TroubleShooter, three light sources, five light markers and a central acquisition system (Dell laptop).

High-speed video camera is a device that allows analyzing video processes in a very short time. This video camera records an image clip with a higher speed then eye can do and afterward plays it back in a very short time, allowing to observe, to measure and to analyze the events (Panagiotakis & Tziritas, 2004). TroubleShooter video camera is produced by Fastec Images Company, and has a maximum video resolution of 640 x 480 pixels and a record speed of 25 to 500 frames/second in normal conditions (see figure 2).

Video camera was embedded on a tripod, perpendicularly on the human subject's movement direction, on an optimal distance of 3500 mm. This distance permits a good visualization of the human subject from down chest's level and implicit correct visualization of all markers mounted on the lower limb.

Minimum illumination for a recording rate of 25 frames/second and a maximum resolution of 640 x 480 pixels is 10 lux. The higher number of frames the higher illumination needed (Rosca & Radu, 2008).

For our experiment we have used a normal optical objective with a focal distance of 12 mm and a recording rate of 250 frames/second with a maximum resolution of 640 x 480 pixels. Because of that, we have used three light sources (halogen light) with a total illumination of 17548.4 lux. Using this video camera and an image software editor (Adobe After Effects), it helps as to determine the lower limb's joints trajectories and the angle between human anatomical segments, during human locomotion.

The light markers are used in combination with a high-speed camera, to determine kinematic parameters of lower limb's joints. There are five markers, which are placed on the hip, knee and ankle joint, on the heel and the second metatarsal's pick. They have a spherical shape, with a 30 mm diameter and they were painted with a special paint, which is highly sensible to the halogen light (see figure 3) (Rosca & Radu, 2008).

Also, the lower limbs of the human subject are dressed up in black-moulded pants because the marker's colour is in highly contrast to the pant's colour. For concluding results, the markers have to be placed exactly on the interest areas, more precisely the marker's centre has to coincide to the joint's centre off rotation, and heel and second metatarsal's markers have to be on the same axis. In advance, to determine the right position of each marker, we have made repetitive palpations of the anatomic areas. Anyway, the marker's placement is relative, that because it's impossible to determine the right position of the joint's centre of rotation and on the other hand because of the relative sliding between moulded pants and skin tegument.

[FIGURE 3 OMITTED]

For a correct interpretation of the recorded movie data, by using geometrical correction equation, we have determinated the maximum error of image deformation, on the vertical and horizontal directions (Rosca & Radu, 2008):

[DELTA]m = 100 x l/L sin [alpha], (1)

where: [DELTA]m is maximum error of image deformation [%], l is the length of light marker [mm] (l = 30 mm), L is the distance between marker centre and objective centre of video camera [mm] and [alpha] is the angle between recording axe and light marker direction movement [[degrees]].

Thus, for a video camera height of approximately 600 mm to the ground, a recording maximum distance of 2130 mm and a distance of 3500 mm between camera central optical axe and the symmetrical axe of light markers, we have determinate that for each marker, for both recording axes, the maximum error of image deformations is 0.857%.

3. CONCLUSIONS

The proposed measuring method is a very simple and efficient method and also quite accurate, that because the recorded images are affected by deformation errors in proportion of 0.857%, which is suitable for the error limits admissible for this measuring method.

The aim of this paper is to design an experimental installation, based on some theoretical information about measuring of locomotion kinematics and the next step of our study is to process all recorded data obtained by using this experimental installation, to determine the kinematic parameters during human locomotion. This is done by using editing software, named Adobe After Effects 6.5 software, in the following scientific paper, called: Image Treatment Process to obtain Kinematic Parameters During Human Locomotion, published in the same proceeding.

4. REFERENCES

Hunt, J.L. & Latam, V. (2006). Control of Biped Locomotion, Springer Publisher, ISSN 0140-0118, Berlin, Germany.

Medved, V. (2001). Measurement of Human Locomotion, Congress Library, ISBN 0-8493-7675-0, USA.

Panagiotakis, C. & Tziritas G. (2004). Recognition and Tracking of the Members of a Moving Human Body, Springer Publisher, ISSN 0302-9743, Berlin, Germany.

Rosca, I.C & Radu, C. (2008). On a Mechatronic System to Determine Dynamic Parameters of the Human Limb During Locomotion Used For Artificial Muscles and Implant Design, 6th International DAAAM Baltic Conference, ISBN 978-9985-59-783-5, Tallin, Estonia.

Vaughan, C.L.; Davis, B.L. & O'Connor, J.C. (1999). Dynamics of Human Gait, Kiboho Publisher, ISBN 0-620-23558-6, Cape Town, South Africa.