Posture Compensated Zero-Moment Point Control Method of the Walking Assistance Apparatus
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With the percentage of elderly people increasing every year, we proposed a walking assistance apparatus for disabled and elderly person, which is used for gait training and rehabilitation. We used zero-moment point (ZMP) control method to ensure stability of the walking assistance apparatus. Since users need to walk on stairs and the distance of every two stairs is invariable, the stride length of the apparatus is supposed to be constant. We compensated ZMP of the apparatus by adjusting the posture and the position of center of gravity (CoG). Thereby, the projection of gravity and inertia force can be maintained in the support polygon. From simulations and experiments, we can adjust the posture of the apparatus and user when instability occurs to prevent the user from stumbling. This method is suitable for walking on flat ground and stairs.Keywords:
Zero moment point
Stairs
Center of gravity
Moment of inertia
Polygon (computer graphics)
Cog
Cog
Center of gravity
Excursion
Force platform
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In this paper, a method for walking stabilization control using a virtual plane method for up-down motion of biped robots is proposed. In the case of the up-down motion in whitch the height of the center of gravity (COG) is not constant, the Zero-Moment Point (ZMP) equation that shows the relation between the ZMP and the COG becomes linear time-variant. Using the proposed method, the ZMP equation is transformed into linear time-invariant. Therefore, the frequency analysis and parameter design of the walking stabilization control can be implemented easily even in the up-down motion. The validity of the proposed method was confirmed by some simulations and experiments.
Cog
Zero moment point
Center of gravity
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In this paper, we discuss COG-correspondent Optimal Body Postures (COBP) of a quadruped robot corresponded with optimal height of the center of gravity (COG) while performing ommidirectional walking on a slope. The COBP is the posture where the moving velocity is maximized corresponding to the height of COG, with respect to the slope and moving direction.The proposed method based on dynamically changing height of COG and body posture during gait-transitions, is used to maintain high robot motion velocity and stability on slope. Through computer simulation, the validity of the proposed method has been demonstrated. The stability has also been confirmed in computer simulation in gait-transition by means of static stability margin.
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Center of gravity
Longitudinal static stability
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Driver fatigue is a cause of serious accidents for heavy machinery operators. Monitoring operator position, as indicated by their Center of Gravity (CoG), may be a means to non-invasively detect driver fatigue. We prototyped a research tool that tracks CoG from four sensors located within the legs of a seat, and validated its accuracy and precision. Our primary contributions are the development of a low-cost integrated CoG detector for seated drivers and the design of a flexure structure to protect load cells from shocks, tensile and shear forces. This system will enable research into CoG as an indicator of fatigue.
Center of gravity
Cog
Operator (biology)
Position (finance)
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This paper presents an emergency stop algorithm of a walking humanoid robot. There are many cases which force a walking robot to stop quickly without falling. Since an emergency occurs at unpredictable timing and at any state of robot, the stopping motion must be generated in real-time. To overcome these problems, our emergency stop motion is divided into four phases according to the role of the zero-moment point (ZMP). In each phase, approximate analytical solutions of the center of gravity (COG) dynamics is used to generate the motion. During the single support phase, a landing time and position are determined by evaluating the average velocity of the swing leg and the horizontal position of the COG. During the double support phase, the travel distance of the COG and the ZMP are evaluated. The validity of the proposed method is confirmed by simulation and experiment using a humanoid robot HRP-2.
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Center of gravity
Zero moment point
Position (finance)
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This paper studies the real-time gait planning for a humanoid robot. By simultaneously planning the trajectories of the COG (Center of Gravity) and the ZMP (Zero Moment Point), the fast and smooth change of gait can be realized. The change of gait is also realized by connecting the newly calculated trajectories to the current ones. While we propose two methods for connecting two trajectories, i.e. the real-time method and the quasi-real-time one, we show that the stable change of gait can be realized by using the quasi-real-time method even if the change of the step position is significant. The effectiveness of the proposed methods are confirmed by simulation and experiment.
Zero moment point
Cog
Center of gravity
Position (finance)
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The referential ZMP (Zero-Moment Point) trajectory that minimizes the variation of COG (Center of Gravity) velocity in the single support phase of a biped robot is shown. Two advantages of using this ZMP trajectory are discussed. The first advantage is that the variation of COG velocity is gradual. The second advantage is that the biped robot enables the heel-contact motion and the toe-off motion in the single support phase. The trajectory planning based on this ZMP trajectory is proposed. In simulation and experiment, the validity of the proposed method was confirmed.
Zero moment point
Cog
Center of gravity
Variation (astronomy)
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The center of gravity (COG) height is an important factor affecting rollover. Earlier studies by the authors assessed the theory of Detection of Three-Dimensional Center of Gravity (D3DCG), which provides an innovative and accurate method for COG height detection. This report describes development of D3DCG, which can be used to prevent rollover accidents by calculating the maximum height of COG and the maximum lateral force that can exist without causing rollover.
For a fixed total weight of a vehicle, the COG height has an upper limit. Based on the law of energy conservation, if the COG height is lower than that upper limit, then the vehicle has potential energy against rollover. When the vehicle is running, road disturbances make its body shake. Some potential energy transfers to the spring energy to provide a restorative force and to make the COG return to its original position. Therefore, when the COG height reaches its maximum value, the potential energy disappears, causing rollover. The highest COG can be expressed according to the principle of the balance of rotational torque. To verify this theory, a COG adjustable experiment is designed with a table-top D3DCG device and a tower object. The total object weight does not change, but its COG height increases until the object cannot maintain stability on the device anymore. Comparison of the real COG and the highest COG confirmed that only when the COG is lower than the highest COG, the object will not roll over.
If a lateral force is acting on a moving object such as a vehicle, then the object will tilt. At the same time, the restoring moment will resist the rolling moment. According to the theory of D3DCG, the lateral force has relation with the rolling angle. When the vehicle starts to roll over, based on the physical structure of moving vehicle, the critical lateral force can be represented by the rolling angle. Therefore, by eliminating the rolling angle as an unknown variable, the maximum lateral force can be expressed by two known variables: the actual COG height and the maximum height of COG. To verify this theory, a remotely controlled truck is made to rotate in a random rotation radius. Then its speed increases gradually until it rolls over. The real-time lateral force is recorded and compared with the calculated maximum lateral force. Results indicate that rollover occurs when the real-time lateral force reaches the maximum lateral force.
This study examines a novel method of rollover prevention without knowing either the total weight, the vehicle speed or turning radius. The accuracy of this theory was well confirmed by comparing the real-time lateral force and the calculated maximum lateral force based on D3DCG.
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Center of gravity
Rollover (web design)
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This paper studies the real-time gait planning for a humanoid robot. By simultaneously planning the trajectories of the COG (center of gravity) and the ZMP (zero moment point), the fast and smooth change of gait, can be realized. The change of gait is also realized by connecting the newly calculated trajectories to the current ones. While we propose two methods for connecting two trajectories, i.e. the real-time method and the quasi-real-time one, we show that the stable change of gait can be realized by using the quasi-real-time method even if the change of the step position is significant. The effectiveness of the proposed methods is confirmed by simulation and experiment.
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An Approach to Human Walking Analysis Based on Balance, Symmetry and Stability Using COG, ZMP and CP
The parameters of walking have been studied from the viewpoints of joint rotation and translation of body. The balance and symmetry of walking are indispensable features to understand for healthy walking, while also being a personal characteristic. However, quantification has not been easy to carry out in the case of the conventional gait parameters COG (center of gravity) and ZMP (zero moment point). In this approach, the CP (crossing point) is proposed to quantify the concept of symmetry and balance by comparing it to the COG and ZMP. The CP is estimated based on the intersection between the hip line and the ankle line. While the hip line is fixed on the upper body where the COG is, the ankle line is altered depending on the each footfall, where the ZMP is. Therefore, the values of COG, ZMP, and CP have similar or different tendencies in terms of whether balanced walking results in symmetry or not. The validity of this is verified by carrying out a simulation with robot walking, and an experiment using human walking. Through additional experiments, it was noticed that the CP was able to improve the role of COG and ZMP in terms of not only stability, but also its relationship with the movement range of the lower limbs.
Cog
Center of gravity
Zero moment point
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