The invention relates to a spherical robot comprising a hull, and within the hull a pendulum mounted on an axle within the hull and a motor for driving the pendulum.

The article "Design and Analysis of a Four-Pendulum Omnidirectional Spherical Robot" by Brian P DeJong et. al., Journal Intell. Robot Syst (2017) 86:3-15 DOI 10.1007/sl0846- 016-0414-4 discloses a four pendulum spherical robot that shifts the robot's center of mass to create rolling torque.

The article "A Spherical Mobile Robot Driven by Eccentric Pendulum and Self-stabilizing by Flywheel" by Han Mao et. al., 2020 17 ^th International Conference on Ubiquitous Robots (UR) June 22 - 26, 2020, Kyoto, Japan discloses a spherical robot driven by pendulums and self-stabilized by flywheel. The spherical robot of this publication is equipped with a heavy pendulum on both sides and to flywheels that can rotate with high speed. By changing the position of the robot center of gravity, the eccentric force is generated to break the static balance of the sphere to achieve rolling motion.

CN 105 181 573 relates to a ground rolling friction coefficient spherical sensor facing an unstructured environment, comprising a spherical shell, wherein the inner surface of the spherical shell is rigidly connected to an output shaft of a drive motor, which drive motor is fixedly connected to a drive motor seat which is connected to an inner surface of the spherical shell through a support rod. The output shaft of the drive motor and the support rod of the drive motor seat are positioned at the same straight line so as to achieve a spherical shell movement control through control of the torque of the drive motor. The drive motor seat is further fixedly connected to a pendulum with a length which is less than the internal radius of the spherical shell. A control module inside the pendulum is applied for controlling the spherical shell movement velocity and calculating the ground rolling friction coefficient under the unstructured environment.

A spherical robot comprising a hull, and within the hull a pendulum mounted on an axle within the hull and a motor for driving the pendulum, wherein over its entire length the axle is placed eccentric of the hull's geometric center, is disclosed by each of US2013/233630, CN 107651 143, CN 102431 605 and by the article by Asiri Samira et al: "The Design and Development of a Dynamic Model of a Low Power Consumption, Two-Pendulum Spherical Robot", IEEE/ASME transactions on Mechatronics, IEEE service center, Piscataway, New Jersey, US, part 24, nr 5, 1 October 2019, pages 2406 - 2415, XP 011751639, ISSN: 1083 - 4435, DOI: 10.1109/TMEC.2019.2934180.

It is an object of the invention to provide a low cost and relatively simple spherical robot, which can nevertheless function in a way comparable to the spherical robots of the prior art.

According to the invention a spherical robot is proposed with the features of one or more of the appended claims.

According to one aspect of the invention, a spherical robot is proposed comprising a hull, and within the hull a pendulum mounted on an axle within the hull and a motor for driving the pendulum, wherein over its entire length the axle on which the pendulum is mounted is placed eccentric of the hull's geometric center, and wherein the robot is arranged such that for at least one specific angle of the pendulum with respect to the hull, the combined center of mass of the hull and the axle counterbalances the center of mass location of the pendulum including the motor, so as to provide that the robot has a combined center of mass which is near or at the geometric center of the spherical hull.

With this design it is possible to have the center of mass of the spherical robot to coincide with its geometric center by setting the motor and thus the pendulum at said specific angle, for example by a controlled or passive locking mechanism, or by using a non-back drivable gearbox and position control of the motor. This is advantageous because it allows the spherical robot to behave like a normal ball for that specific angle only. Thereby, once rolling, the spherical robot can continue rolling for some distance without consuming more energy than a comparable rolling ball, so that it can even be perceived by human users as a conventional ball whenever that may be desired.

When the center of mass of the spherical robot does not coincide with its geometric center, the eccentric placement of the pendulum with respect to the hull's geometric center provides imbalance and creates during rotation of the axle centrifugal and Coriolis effects which allows movement of the spherical robot into two orthogonal horizontal directions. This is particularly advantageous and surprising since according to another aspect of the invention it is possible and accordingly preferred to embody the spherical robot with a single motor only.

Preferably the (single) motor is mounted on or in the pendulum. This motor placement aids in maximizing the ratio between mass of the pendulum and mass of the hull. At least one of the batteries, electronics and control for the motor can also be provided inside the pendulum. Further it is preferred that the motor has its output shaft mounted on the axle.

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of a spherical robot according to the invention that is not limiting as to the appended claims.

In the drawing of a single figure the spherical robot of the invention is shown.

The figure shows a spherical robot 1 comprising a hull 2, and within the hull 2 a pendulum 3 mounted on an axle 4 within the hull 2 and a motor 5 for driving the pendulum 3. Over its entire length the axle 4 is placed eccentric of the hull's geometric center 7. The motor 5 is indicated at its preferable position mounted inside the pendulum 3, with the motor output shaft connected to the axle 4. It further shows that the motor 5 is the only motor of the robot 1.

Preferably, the motor 5 includes a gearbox (not shown) that enables mounting the motor 5 at a 90-degree angle to the axle 4, or another type of transmission such as a belt drive, such that the center of mass of the motor 5 is maximally displaced from the axle 4. This increases the pendulum effect.

The motor 5 can be controlled using a sensor (not shown) mounted to the pendulum 3 or a set of sensors mounted to the hull 2 and to the pendulum 3. Preferably the sensor or sensors are mounted to the pendulum 3 only, because that reduces cost and makes it easier to provide power to the sensor(s). The application of a sensor or sensors improves control performance of the robot 1, by arranging that the at least one sensor connects to the electronics and control for the motor 5. It is however also possible to control the robot 1 without any sensor that measures the relative angle between pendulum 3 and hull 2.

It is found that in order to make the robot 1 roll in any desired direction, it is sufficient to measure an absolute orientation of the pendulum 3 with respect to a reference. Such a reference may be the direction of gravity or may be provided by a complete inertial coordinate system. This makes the robot

1 very cost-effective.

The sensor for determining the orientation of the pendulum 3 can for example be embodied as an inertial measurement unit. Optionally the sensor comprises one of an accelerometer, a gyroscope, and a magnetometer.

In one embodiment the sensor is a 3-axis accelerometer mounted to the pendulum 3. This enables to use a minimal configuration for the controller.

In some embodiments, the robot may use a multitude of sensors either in the hull 2 or in the pendulum 3 or in both, which sensors and associated control enable the robot to interact with the environment, for example to detect moving objects or users from visual or auditory cues (using laser, radar, stereo microphones, etc.) and to react to these.

The spherical robot 1 of the invention has the property that for at least one specific angle of the pendulum 3 with respect to the hull 2, the combined center of mass of the hull

2 and axle 4 counterbalances the center of mass location of the pendulum 3 including the motor 5, in such a way that the combined center of mass of the robot 1 is approximately at the geometric center 7 of the spherical hull 2.

Further it is preferred that for at least one specific angle of the pendulum 3 with respect to the hull 2, the mass distributions of the hull 2 and axle 4 precisely counterbalance the mass distribution of the pendulum 3 including the motor 5, in such a way that the combined inertia tensor of the robot is approximately diagonal and contains approximately identical values, which means the robot is then mechanically equivalent to a sphere.

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the spherical robot of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment.