A ball balancing robot also known as a ballbot is a dynamically-stable mobile robot designed to balance on a single spherical wheel (i.e., a ball). Through its single contact point with the ground, a ballbot is omnidirectional and thus exceptionally agile, maneuverable and organic in motion compared to other ground vehicles. Its dynamic stability enables improved navigability in narrow, crowded and dynamic environments. The ballbot works on the same principle as that of an inverted pendulum.
The first successful ballbot was developed in 2005 [6] [7] [8] by Prof. Ralph Hollis of the Robotics Institute at Carnegie Mellon University (CMU), Pittsburgh, USA and it was patented in 2010. [9] The CMU Ballbot [8] [10] [11] [12] is built to be of human size, both in height and footprint. Prof. Hollis and his group at CMU demonstrated that the ballbot can be robust to disturbances including kicks and shoves, and can also handle collisions with furniture and walls. [13] [14] [15] They showed that a variety of interesting human-robot physical interaction behaviors can be developed with the ballbot, [16] [17] and presented planning and control algorithms to achieve fast, dynamic and graceful motions using the ballbot. [18] [19] [20] They also demonstrated the ballbot's capability to autonomously navigate human environments to achieve point-point and surveillance tasks. [21] [22] [23] A pair of two degrees of freedom (DOF) arms was added to the CMU Ballbot [8] in 2011, making it the first and currently, the only ballbot in the world with arms. [24] [25] [26]
In 2005, around the same time when CMU Ballbot [8] was introduced, a group of researchers at University of Tokyo independently presented the design for a human-ridable ballbot wheelchair that balances on a basketball named "B. B. Rider". [27] However, they reported only the design and never presented any experimental results. [27] Around the same time, László Havasi from Hungary independently introduced another ballbot called ERROSphere. [28] The robot did not reliably balance and no further work was presented.
Since the introduction of CMU Ballbot [8] in 2005, several other groups around the world have developed ballbots. Prof. Masaaki Kumagai developed BallIP in 2008 [29] at Tohoku Gakuin University, Japan. Prof. Kumagai and his group demonstrated the capability of ballbots to carry loads and be used for cooperative transportation. [30] They developed a number of small ballbots and demonstrated cooperative transportation using them. [30] [31] A group of mechanical engineering students at ETH Zurich, Switzerland developed Rezero in 2010. [32] Rezero re-emphasized the fast and graceful motions that can be achieved using ballbots. [33]
Tomás Arribas (Spain) developed the first ballbot using LEGO Mindstorms NXT in 2008 as the Master Project at University of Alcala. [34] [35] He developed a simulation project with Microsoft Excel to easily simulate the system. [36] As part of the research carried out inside the Space Research Group of the University of Alcalá (SRG-UAH), Spain, the work team, specialised in optimal control and planning applied to non-linear dynamic systems, published in 2012 the article called "A Monoball Robot Based on LEGO Mindstorms" [37] This article describes the math model and trajectory control as a baseline to unstable and non-linear control systems.
Yorihisa Yamamoto (Japan) inspired by Tomás Arribas's project, developed a ballbot using LEGO Mindstorms NXT in 2009. [38] [39] He created a detailed demo to build, model and create controllers using MATLAB. [38] A group of mechanical engineering students at University of Adelaide (Australia) developed both a LEGO ballbot and a full-scale ballbot in 2009. [40] A group of students from ITMO University (Russia) introduced an algorithm and constructed a ballbot based on LegoNXT robotics kit which performed stability with only two actuators used. [41] Videos on YouTube present ballbots developed around the world. Some of them have been developed using LEGO Mindstorms NXT. [42] [43] [44] [45] [46] Other custom designs use omni-wheels to actuate the ball. [47] [48] [49] [50]
Thomas Kølbæk Jespersen (Denmark) developed the Kugle ballbot as his final master thesis in 2019. [51] The Kugle ballbot is a human-sized ballbot developed as part of an ongoing Human Robot Interaction research project at Aalborg University. Equipped with three motors and omniwheels, an onboard Intel NUC, two SICK LiDARs, an ARM microprocessor and a tablet on the top, the robot is capable of maneuvering autonomously in indoor environments and guide people around. The master thesis takes a different approach to the system modelling by deriving a non-linear quaternion-based dynamic model which is used to derive a non-linear sliding mode controller to stabilize the balance and a path-following model predictive controller to plan and execute smooth trajectories. The complete master thesis and all material including MATLAB source code and C++ controller implementations are publicly available on GitHub. [52]
Ballbots have also appeared in the science fiction world. Pixar's 2008 movie Wall-E featured "M-O" (Microbe Obliterator), a ballbot cleaning robot. Syfy's 2010 TV series Caprica featured "Serge", a ballbot butler robot. [53]
Historically, mobile robots have been designed to be statically stable, which results in the robot not needing to expend energy while standing still. This is typically achieved through the use of three or more wheels on a base. In order to avoid tipping, these statically-stable mobile robots have a wide base for a large polygon of support, and a lot of dead weight in the base to lower the center of gravity. They also tend to have low acceleration or deceleration to avoid tipping. The wide base makes it difficult for statically-stable mobile robots to navigate cluttered human environments. Moreover, these robots have several other limitations that make them poorly suited to a constantly changing human environment. They can neither roll in any direction, nor can they turn in place. [8]
The desire to build tall and narrow mobile robots that do not tip over led to development of balancing mobile robots like the ballbot. A ballbot generally has a body that balances on top of a single spherical wheel (ball). It forms an underactuated system, i.e., there are more degrees of freedom (DOF) than there are independent control inputs. The ball is directly controlled using actuators, whereas the body has no direct control. The body is kept upright about its unstable equilibrium point by controlling the ball, much like the control of an inverted pendulum. [8] This leads to limited but perpetual position displacements of the ballbot. The counter-intuitive aspect of the ballbot motion is that in order to move forward, the body has to lean forward and in order to lean forward, the ball must roll backwards. All these characteristics make planning to achieve desired motions for the ballbot a challenging task. In order to achieve a forward straight line motion, the ballbot has to lean forward to accelerate and lean backward to decelerate. [14] [18] [24] [32] Further, the ballbot has to lean into curves in order to compensate for centripetal forces, which results in elegant and graceful motions. [18] [22] [24] [32]
Unlike two-wheeled balancing mobile robots like Segway that balance in one direction but cannot move in the lateral direction, the ballbot is omni-directional and hence, can roll in any direction. It has no minimal turning radius and does not have to yaw in order to change direction.
The most fundamental design parameters of a ballbot are its height, mass, its center of gravity and the maximum torque its actuators can provide. The choice of those parameters determine the robot's moment of inertia, the maximum pitch angle and thus its dynamic and acceleration performance and agility. The maximum velocity is a function of actuator power and its characteristics. Besides the maximum torque, the pitch angle is additionally upper bounded by the maximum force which can be transmitted from the actuators to the ground. Therefore, friction coefficients of all parts involved in force transmission also play a major role in system design. Also, close attention has to be paid to the ratio of the moment of inertia of the robot body and its ball in order to prevent undesired ball spin, especially while yawing. [32]
The ball is the core element of a ballbot, it has to transmit and bear all arising forces and withstand mechanical wear caused by rough contact surfaces. A high friction coefficient of its surface and a low inertia are essential. The CMU Ballbot, [8] Rezero [32] and Kugle [51] used a hollow metal sphere with poly-urethane coating. B.B. Rider [27] used a basketball, while BallIP [29] and Adelaide Ballbot [40] used bowling balls coated with a thin layer of rubber.
In order to solve the rather complex problem of actuating a sphere, a variety of different actuation mechanisms have been introduced. The CMU Ballbot [8] used an inverse mouse-ball drive mechanism. Unlike the traditional mouse ball that drives the mouse rollers to provide computer input, the inverse mouse-ball drive uses rollers to drive the ball producing motion. The inverse mouse-ball drive uses four rollers to drive the ball and each roller is actuated by an independent electric motor. In order to achieve yaw motion, the CMU Ballbot uses a bearing, slip-ring assembly and a separate motor to spin the body on top of the ball. [14] The LEGO Ballbot [38] also used an inverse mouse-ball drive, but used normal wheels to drive the ball instead of rollers.
Unlike CMU Ballbot [14] both BallIP, [29] Rezero [32] and Kugle [51] use omni-wheels to drive the ball. This drive mechanism does not require a separate yaw drive mechanism and allows direct control of the yaw rotation of the ball. Unlike CMU Ballbot [14] that uses four motors for driving the ball and one motor for yaw rotation, BallIP, [29] Rezero [32] and Kugle [51] use only three motors for both the operations. Moreover, they only have three force transmission points compared to four points on CMU Ballbot. Since the contact between an omni-wheel and the ball should be reduced to a single point, most available omni-wheels are not properly suitable for this task because of the gaps between the individual smaller wheels that result in an unsteady rolling motion. Therefore, the BallIP [29] project introduced a more complex omni-wheel with a continuous circumferential contact line. The Rezero [32] team equipped this omni-wheel design with roller bearings and a high-friction coating. [32] They also additionally fitted a mechanical ball arrester that presses the ball against the actuators in order to further increase friction forces and a suspension to dampen vibrations. [32] The Kugle robot is equipped with a skirt which holds the ball in place to avoid that the ball gets pushed out during large inclinations. The Adelaide Ballbot [40] uses wheels for its LEGO version and traditional omni-wheels for its full-scale version.
Prof. Masaaki Kumagai, [3] who developed BallIP [29] introduced another ball drive mechanism that uses partially sliding rollers. [54] [55] The objective of this design was to develop 3-DOF actuation on the ball using a low cost mechanism.
In order to actively control the position and body orientation of a ballbot by a sensor-computer-actuator framework, beside a suitable microprocessor or some sort of other computing unit to run the necessary control loops, a ballbot fundamentally requires a series of sensors which allow to measure the orientation of the ball and the ballbot body as a function of time. To keep track of the motions of the ball, rotary encoders (CMU Ballbot, [8] BallIP, [29] Rezero, [32] Kugle [51] ) are usually used. Measuring the body orientation is more complicated and is often done by the use of gyroscopes (NXT Ballbots [38] [40] ) or, more generally, an Inertial Measurement Unit (CMU Ballbot, [8] BallIP, [29] Rezero, [32] Kugle [51] ) which includes an accelerometer, gyroscope and possibly magnetometer whose measurements are fused into the body orientation through AHRS algorithms.
The CMU Ballbot [8] uses a Hokuyo URG-04LX Laser Range Finder to localize itself in a 2D map of the environment. [22] [23] It also uses the laser range finder for detecting obstacles and avoiding them. [22] [23] Conversely the Kugle robot [51] uses two SICK TiM571 2D LiDAR to localize itself, perform obstacle avoidance and detect people for guidance.
The CMU Ballbot [8] is the first and currently, the only ballbot to have arms. [24] [25] [26] It has a pair of 2-DOF arms that are driven by series-elastic actuators. The arms are hollow aluminium tubes with a provision to add dummy weights at their ends. In their present state, the arms cannot be used for any significant manipulation, but are used to study their effects on the dynamics of ballbot. [24] [25] [26]
The mathematical MIMO-model which is needed in order to simulate a ballbot and to design a sufficient controller which stabilizes the system, is very similar to an inverted pendulum on a cart. The LEGO NXT Ballbot, [38] Adelaide Ballbot, [40] Rezero [32] and Kugle [51] include actuator models in their robot models, whereas CMU Ballbot [8] neglects the actuator models and models the Ballbot as a body on top of a ball. Initially, CMU Ballbot [8] used two 2D planar models in perpendicular planes to model the ballbot [13] [14] and at present, uses 3D models without yaw motion for both the ballbot without arms [18] [21] [22] and the ballbot with arms. [24] BallIP [29] uses a model that describes the dependence of the ball position on the wheel velocities and the body motion. Rezero [32] uses a full 3D model that includes yaw motion too. Kugle [51] uses a fully coupled quaternion-based 3D model which couples the motion of all axes.
The ballbots (CMU Ballbot, [8] BallIP, [29] NXT Ballbot, [38] Adelaide Ballbot, [40] Rezero [32] ) use linear feedback control approaches to maintain balance and achieve motion. The CMU Ballbot [8] uses an inner balancing control loop that maintains the body at desired body angles and an outer loop controller that achieves desired ball motions by commanding body angles to the balancing controller. [13] [14] [18] [21] [22] [24] The Kugle robot is tested with both linear feedback controllers (LQR) and non-linear sliding mode controllers to show the benefit of its coupled dynamic quaternion model. [51]
A ballbot is a shape-accelerated underactuated system. The inclination angles of a ballbot is thus dynamically linked to the resulting accelerations of the ball and robot leading to an underactuated system. The CMU Ballbot plans motions in the space of body lean angles in order to achieve fast, dynamic and graceful ball motions. [18] [21] [22] [24] With the introduction of arms, CMU Ballbot uses its planning procedure to plan in the space of both body lean angles and arm angles to achieve desired ball motions. [22] [24] [25] Moreover, it can also account for cases where the arms are constrained to certain specific motions and only body angles have to be used to achieve desired ball motions. [26] The CMU Ballbot uses an integrated planning and control framework to autonomously navigate human environments. [22] [23] Its motion planner plans in the space of controllers to produce graceful navigation, and achieves point-point and surveillance tasks. It uses the laser range finder to actively detect and avoid both static and dynamic obstacles in its environment. [22] [23]
For Kugle a path-planning model predictive controller (MPC) is designed to control the inclination angles of the ballbot to follow a given path. A path-following strategy is chosen over common trajectory or reference tracking controllers to accommodate for the temporally lacking behaviour of ballbots due to the underactuated nature. The path is parameterized as a polynomial and included into the cost-function of the MPC. A set of soft-constraints ensures that obstacles are avoided and that progress is made with a desired speed. [51]
The biggest concern with a ballbot is its safety in case of a system failure. There have been several attempts in addressing this concern. The CMU Ballbot [8] introduced three retractable landing legs that allow the robot to remain standing (statically-stable) after being powered down. It is also capable of automatically transitioning from this statically-stable state to the dynamically-stable, balancing state and vice versa. [13] [15] Rezero featured a roll-over safety mechanism in order to prevent serious damage in case of a system failure. [32]
Due to its dynamic stability, a ballbot can be tall and narrow, and can also be physically interactive, making it an ideal candidate for a personal mobile robot. [8] It can act as an effective service robot at homes and offices and offer guidance to people in e.g. malls and airports. [51] The present day ballbots [8] [29] [32] are restricted to smooth surfaces. The concept of the ballbot has attracted a lot of media attention, [10] [11] [12] [31] [33] and several ballbot characters have appeared in Hollywood movies. [56] [53] Hence, the ballbot has a variety of applications in the entertainment industry, including toys.
A humanoid robot is a robot resembling the human body in shape. The design may be for functional purposes, such as interacting with human tools and environments, for experimental purposes, such as the study of bipedal locomotion, or for other purposes. In general, humanoid robots have a torso, a head, two arms, and two legs, though some humanoid robots may replicate only part of the body, for example, from the waist up. Some humanoid robots also have heads designed to replicate human facial features such as eyes and mouths. Androids are humanoid robots built to aesthetically resemble humans.
leJOS is a firmware replacement for Lego Mindstorms programmable bricks. Different variants of the software support the original Robotics Invention System, the NXT, and the EV3. It includes a Java virtual machine, which allows Lego Mindstorms robots to be programmed in the Java programming language. It also includes 'iCommand.jar' which allows you to communicate via bluetooth with the original firmware of the Mindstorm. It is often used for teaching Java to first-year computer science students. The leJOS-based robot Jitter flew around on the International Space Station in December 2001.
Motion control is a sub-field of automation, encompassing the systems or sub-systems involved in moving parts of machines in a controlled manner. Motion control systems are extensively used in a variety of fields for automation purposes, including precision engineering, micromanufacturing, biotechnology, and nanotechnology. The main components involved typically include a motion controller, an energy amplifier, and one or more prime movers or actuators. Motion control may be open loop or closed loop. In open loop systems, the controller sends a command through the amplifier to the prime mover or actuator, and does not know if the desired motion was actually achieved. Typical systems include stepper motor or fan control. For tighter control with more precision, a measuring device may be added to the system. When the measurement is converted to a signal that is sent back to the controller, and the controller compensates for any error, it becomes a Closed loop System.
Passive dynamics refers to the dynamical behavior of actuators, robots, or organisms when not drawing energy from a supply. Depending on the application, considering or altering the passive dynamics of a powered system can have drastic effects on performance, particularly energy economy, stability, and task bandwidth. Devices using no power source are considered "passive", and their behavior is fully described by their passive dynamics.
A mobile robot is an automatic machine that is capable of locomotion. Mobile robotics is usually considered to be a subfield of robotics and information engineering.
Six degrees of freedom (6DOF), or sometimes six degrees of movement, refers to the six mechanical degrees of freedom of movement of a rigid body in three-dimensional space. Specifically, the body is free to change position as forward/backward (surge), up/down (heave), left/right (sway) translation in three perpendicular axes, combined with changes in orientation through rotation about three perpendicular axes, often termed yaw, pitch, and roll.
Underactuation is a technical term used in robotics and control theory to describe mechanical systems that cannot be commanded to follow arbitrary trajectories in configuration space. This condition can occur for a number of reasons, the simplest of which is when the system has a lower number of actuators than degrees of freedom. In this case, the system is said to be trivially underactuated.
Lego Mindstorms NXT is a programmable robotics kit released by Lego on August 2, 2006. It replaced the Robotics Invention System, the first-generation Lego Mindstorms kit. The base kit ships in two versions: the retail version and the education base set. It comes with the NXT-G programming software or the optional LabVIEW for Lego Mindstorms. A variety of unofficial languages exist, such as NXC, NBC, leJOS NXJ, and RobotC. A second-generation set, Lego Mindstorms NXT 2.0, was released on August 1, 2009, with a color sensor and other upgrades. The third-generation EV3 was released in September 2013.
Adaptable Robotics refers to a field of robotics with a focus on creating robotic systems capable of adjusting their hardware and software components to perform a wide range of tasks while adapting to varying environments. The 1960s introduced robotics into the industrial field. Since then, the need to make robots with new forms of actuation, adaptability, sensing and perception, and even the ability to learn stemmed the field of adaptable robotics. Significant developments such as the PUMA robot, manipulation research, soft robotics, swarm robotics, AI, cobots, bio-inspired approaches, and more ongoing research have advanced the adaptable robotics field tremendously. Adaptable robots are usually associated with their development kit, typically used to create autonomous mobile robots. In some cases, an adaptable kit will still be functional even when certain components break.
Legged robots are a type of mobile robot which use articulated limbs, such as leg mechanisms, to provide locomotion. They are more versatile than wheeled robots and can traverse many different terrains, though these advantages require increased complexity and power consumption. Legged robots often imitate legged animals, such as humans or insects, in an example of biomimicry.
A spherical robot, also known as spherical mobile robot, or ball-shaped robot is a mobile robot with spherical external shape. A spherical robot is typically made of a spherical shell serving as the body of the robot and an internal driving unit (IDU) that enables the robot to move. Spherical mobile robots typically move by rolling over surfaces. The rolling motion is commonly performed by changing the robot's center of mass, but there exist some other driving mechanisms. In a wider sense, however, the term "spherical robot" may also be referred to a stationary robot with two rotary joints and one prismatic joint which forms a spherical coordinate system.
Urbi is an open-source cross-platform software computing platform written in C++ used to develop applications for robotics and complex systems. Urbi is based on the UObject distributed C++ component architecture. It also includes the urbiscript orchestration language which is a parallel and event-driven script language. UObject components can be plugged into urbiscript and appear as native objects that can be scripted to specify their interactions and data exchanges. UObjects can be linked to the urbiscript interpreter, or executed as autonomous processes in "remote" mode.
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots. Robotics is related to the sciences of electronics, engineering, mechanics, and software.
Robotics is the interdisciplinary study and practice of the design, construction, operation, and use of robots.
The following outline is provided as an overview of and topical guide to robotics:
Surena is a series of Iranian humanoid robots, named after the Parthian General Surena. The Institute of Electrical and Electronics Engineers (IEEE) has placed the Surena among the prominent robots in the world after analyzing its performance.
Oussama Khatib is a roboticist and a professor of computer science at Stanford University, and a Fellow of the IEEE. He is credited with seminal work in areas ranging from robot motion planning and control, human-friendly robot design, to haptic interaction and human motion synthesis. His work's emphasis has been to develop theories, algorithms, and technologies, that control robot systems by using models of their physical dynamics. These dynamic models are used to derive optimal controllers for complex robots that interact with the environment in real-time.
A juggling robot is a robot designed to be able to successfully carry out bounce or toss juggling. Robots capable of juggling are designed and built both to increase and test understanding and theories of human movement, juggling, and robotics. Juggling robots may include sensors to guide arm/hand movement or may rely on physical methods such as tracks or funnels to guide prop movement. Since true juggling requires more props than hands, many robots described as capable of juggling are not.
A high performance positioning system (HPPS) is a type of positioning system consisting of a piece of electromechanics equipment (e.g. an assembly of linear stages and rotary stages) that is capable of moving an object in a three-dimensional space within a work envelope. Positioning could be done point to point or along a desired path of motion. Position is typically defined in six degrees of freedom, including linear, in an x,y,z cartesian coordinate system, and angular orientation of yaw, pitch, roll. HPPS are used in many manufacturing processes to move an object (tool or part) smoothly and accurately in six degrees of freedom, along a desired path, at a desired orientation, with high acceleration, high deceleration, high velocity and low settling time. It is designed to quickly stop its motion and accurately place the moving object at its desired final position and orientation with minimal jittering.
A continuum robot is a type of robot that is characterised by infinite degrees of freedom and number of joints. These characteristics allow continuum manipulators to adjust and modify their shape at any point along their length, granting them the possibility to work in confined spaces and complex environments where standard rigid-link robots cannot operate. In particular, we can define a continuum robot as an actuatable structure whose constitutive material forms curves with continuous tangent vectors. This is a fundamental definition that allows to distinguish between continuum robots and snake-arm robots or hyper-redundant manipulators: the presence of rigid links and joints allows them to only approximately perform curves with continuous tangent vectors.
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