1. Field of the Invention
The present invention pertains to a dynamically walking humanoid robot. More specifically, the present invention is directed to method for controlling a humanoid robot in a walking state, a standing state, and during transitions between states.
2. Description of the Related Art
Humanoid Robots have many potential applications in many different fields. They have the potential to do tasks that are dull, dangerous, or dirty for humans. They also have started to play a role in the entertainment, advertising, and hobby industries.
Various humanoid robots, and their associated control algorithms, have been developed to various degrees of proficiency. Some humanoid robots are capable of walking, running, going up stairs, and manipulating objects.
However, most humanoid robots lack a sufficient degree of balance to be useful in real world environments, particularly environments in which footholds are limited and disturbances are prevalent. The lack of balance and disturbance recovery provided by current humanoid robot platforms has greatly limited their widespread use.
Some of the current humanoid robots include the Honda Asimo robot, the Toyota partner robot, the Hubo robot, the Sarcos humanoid, and the Boston Dynamics Petman Robot. Most of these robots have not demonstrated walking that is robust to disturbances, such as pushes, nor have demonstrated walking with limited available footholds, such as over stepping stones. None of them have demonstrated walking with limited available footholds in the presence of disturbances.
FIG. 3 depicts a representative bipedal robot that is useful when considering the complexity of controlled bipedal motion. Body 32 is joined to thighs 55, 56 by a pair of powered hip joints 61, 62. Although the hip joints primarily pivot in the swing plane of the legs, they may have other degrees of freedom as well.
Thighs 55, 56 are joined to lower legs 57, 58 by a pair of powered knee joints 71, 72. Feet 54, 55 are joined to lower legs 57, 58 by a pair of powered ankle joints 57, 58. The powered ankle joints have multiple degrees of freedom, typically including roll and pitch. Each foot provides a platform from which an ankle joint can apply torque to a lower leg.
The control of a system such as shown in FIG. 3 is an extraordinarily complex problem. The prior art has generally focused on increasing the sophistication of the sensor and actuation technology used. Such systems seek to know the current state of each limb and joint—monitoring multiple degrees of freedom. The control systems then traditionally use a trajectory tracking approach of calculating and driving a desired position for each component in the multi-limbed system.
This approach is not very robust to variations (and errors) in the sensors and actuators, or when a large disturbance is introduced. It is apparent that human beings do not control motion with extremely high precision and likely do not employ a trajectory tracking approach. Human motion seems to be inherently based on a less precise, and more compliant control system. Yet, human beings are able to move successfully in a wide variety of circumstances. We are resistant to disturbing forces and able to “solve” the balance problem even when the conditions change drastically in mid-stride.
FIG. 1 illustrates standing human 22. The goal of the standing human is to maintain a balanced stance. If a mild disturbance is introduced—such as a gentle lateral shove—the person will be able to maintain a balanced stance without moving the feet. However, if a larger lateral shove is applied, the person will have to take one or more steps in order to prevent a fall.
The concept of “viability” has application to this scenario. If preventing a fall is the goal, then any state from which a fall can be prevented is a viable state. In some states the person can take a single step to regain a balanced stance. For a more severe disturbance the person will have to take two steps to regain a static and balanced stance. The first of these two steps cannot produce a balanced state but it is a “viable” state since it leads to a second step which will produce a balanced state.
The left side of FIG. 1 graphically depicts several possible capture regions 26. The region labeled “N=1” is the area in which the user can take a single step and obtain a static and balanced stance. The region labeled “N=2” is the region in which it is possible for the user to step and then obtain a balanced state in two total steps. The region labeled “N=3” is the region in which it is possible to take a step and then obtain a balanced state in three total steps.
The right side of FIG. 1 depicts the same scenario for a person in a running state. Running human 24 has a center of mass 84 which is moving in the direction indicated by the arrow. The one-step capture region lies well in front of the present position. This fact is intuitively true as all people understand that if one is running and one wishes to take a single step and then come to a balanced halt over that step, one must make that step well in front of the present position.
The present invention presents a novel approach to controlling bipedal motion in which robust control is demonstrated using a relatively small amount of input information. Several factors are combined to define a known region in which motion or balance is viable. FIG. 2 shows a very simplified depiction of this objective. In FIG. 2, a one step capture region 26 has been superimposed on areas that are available for stepping (in this case stepping stones 40). Those portions of the stepping stones lying within capture region 26 represent viable options and those lying outside do not. The invention uses some basic assumptions about the nature of bipedal motion to simplify the task of determining viable options for continued balance.