A MINIATURIZED MICROROBOTIC DEVICE FOR LOCOMOTION IN A LIQUID

ENVIRONMENT

DESCRIPTION

Field of the Invention

The present invention relates generally to the field of microrobotic devices and more precisely refers to a miniaturized device capable of autonomous or controlled movement for the purpose of studying and analysing physical and/or chemical parameters in a liquid environment.

Background Art

As used in the present specification, the term microrobotics is intended relative to the design and manufacture of robotic systems and components with milimetric and micrometric dimensions. In the same manner, with the term microrobot we mean a robotic device characterised by the aforementioned dimensions and containing a control unit, a power source and actuating means for its propulsion and orientation.

Existing devices that are capable of moving and carrying out activities in liquid environments are usually autonomous or teleoperated submarines for the analysis of sea beds or pipelines, like for example the autonomous submarine described in US2007125289 or the submersible toy described in US4241535 capable of swimming in water thanks to the action of a propeller and a rudder. However, the size of these devices (from 30 cm upwards, as linear dimensions) limits their field of application to only macroscopic systems, excluding hydraulic systems with small dimensions. Indeed, none of the systems of this type known in the art can be scaled down to dimensions of tens of millimetres.

Robots with dimensions of a few tens of millimetres or less have been proposed especially for applications in the biomedical field. Various solutions were adopted for the locomotion of these robots. Robots have been foreseen exploiting conventional locomotion methods, generally propellers (usually one or two propellers to obtain the hydrodynamic thrust) and rudders for giving a direction to the movement, even in miniaturized versions (G. Tortora et al., Propeller-based wireless device for active capsular endoscopy in the gastric district, MITAT, Vol. 18, No. 5, pp. 280-290, 2009). Biomimetic systems have also been proposed, for example equipped with mechanical flagella [B. Behkam et al., Modelling and testing of a biomimetic flagellar propulsion method for microscale biomedical swimming robots, 2005 Proc. of the IEEE/ASME Int. Conf. on Adv. Intelligent Mechatronics, pp.37-42], as well as biohybrid systems, obtained by integrating, for example, biological propulsion systems with artificial elements, as described in US2006073540.

Other robots with biomimetic locomotion systems, inspired by fishes or other aquatic organisms or in general by systems which move a tail, and by lampreys or salamanders, are described for example in Z.G.Zhang et al., Electrostatically actuated robotic fish, IEEE Transactions on Robotics vol. 24, no. 1 , pp.1 18-129, Feb. 2008; B. Kim et al., A biomimetic undulatory tadpole robot using ionic-polimer metal composite actuators, Smart Material and Structures, vol. 14, no. 6, pp.1579-1585, Nov. 2005; C. Stefanini et al., A mechanics for biomimetic actuation in lamprery-like robots, 2006, Proc. of the First IEEE/RAS-EMBS Int. Conf. on Biomedical Robotics and Biomechatronics, pp. 579-584.

For the actuation of the locomotion members various types of actuators have been proposed, such as electromagnets, piezoelectric devices and active composite materials. With regard to magnetic actuation, some solutions have been proposed based upon more complex mechanisms and that are on a greater scale. These devices are based upon the elementary magnetic interaction mechanism for which an attractive or repulsive force is generated according to the spatial arrangement of the permanent magnets. On this subject, see for example, JP2007260423, US2006169293 and WO2007040269.

However, none of the robotic devices of the type described above, whether it be due to the complexity of their actuation mechanisms, or due to the same configuration of the means that produce the locomotion movement, can be miniaturized to dimensions below 1 -2 cm.

The object of the present invention is to provide a microrobotic device that is capable of autonomously moving in a liquid environment using locomotion means that are simple and compact and that can thus be highly miniaturized. A particular object of the present invention is to provide a micro robotic device of the aforementioned type that is capable of exhibiting a complex collective behaviour if used in swarms.

Summary of the Invention

These objects are achieved with the microrobotic device according to the present invention the characteristics of which are set forth in claim 1 . Further important features are set forth in the dependent claims.

The microrobotic device according to the present invention is of the capsule type and uses a plurality of flexible elements, for example in the form of appendages or wings, made from polymeric, magnetised or magnetisable material or enclosing magnets or particles with magnetic properties in their structure. The flexible elements are mounted on the side surface of the capsule and the repulsive or attractive interaction between magnetic forces generated on them and the force induced by a variable magnetic field inside the capsule causes a reciprocating, undulatory movement of the flexible elements. Such a variable magnetic field can be generated both by the rotation or translation of a permanent magnet by means of a motor, and from microcoils.

The microrobotic device of the present invention achieves a biomimetic locomotion that can be compared to the swimming of a jelly fish, or in any case of a finned system, exploiting an innovative principle through which the variation of a magnetic field inside the device determines the variation of the configuration of mobile flexible elements positioned on the capsule body of the device. The movement of these flexible elements generates forces on the surrounding medium, which provide the movement of the device in a predetermined direction.

Brief description of the drawings

Further characteristics and the advantages of the microrobotic device according to the present invention will be apparent from the following description of an exemplifying, non-limiting embodiment thereof made with reference to the attached drawings, in which:

figure 1 is a schematic perspective view of the microrobotic device according to the invention; figure 2 is a longitudinal sectional view of the device of figure 1 .

With reference to the aforementioned figures, the device of the invention comprises a housing 1 having the form of a substantially cylindrical hollow body extending along a longitudinal axis X in the present embodiment of the invention. The housing 1 has a forward end 1 a and a rear end 1 b that are closed and substantially aligned along said axis. Inside the housing body 1 a power source 2 is arranged, comprising a battery (for example a lithium-ion battery) or a system which can be fed from outside, and an electronic card 8, equipped with a microcontroller for controlling the means for moving the device described herebelow. Inside the housing body 1 , in a substantially longitudinal position, a micromotor 3 is also arranged, the drive shaft of which is directly connected to a rotor 4, arranged close to the rear end 1 b of the housing body 1 and lying on a plane that is perpendicular to the axis X of the body, said axis thus being also the rotation axis of the rotor 4.

In the present embodiment of the invention the side surface of the rotor 4 has a substantially polygonal shape and angularly equispaced seats 4a are formed on the side surface. Each seat 4a houses a magnet 5 (for example of the NdFeB type). In particular, the illustrated embodiment comprises a rotor 4 with an octagonal shape and four magnets 5 arranged in respective seats 4a formed on alternate faces of the side surface of the rotor 4.

Outside of the housing body 1 four flexible wings 6, also equally spaced angularly, are attached. In particular each wing 6 is attached with an end 6a thereof near to the forward end 1 a of the housing 1 and projects along the housing body 1 up to its rear end 1 b. The opposite end 6b of each wing is free to move and bend in a direction that is radial with respect to the longitudinal axis X and houses a respective magnet 7 (for example of the NdFeB type).

The locomotion movement of the microrobotic device according to the invention is generated by the interaction between the permanent magnets 5 arranged on the rotor 4 and the permanent magnets 7 arranged on the wings 6, when the rotor 4 is set in rotation by the micromotor 3. The rotation of the rotor 4 generates a variable magnetic field that interacts with the magnetised portions of the wings 6 causing them to bend and subsequently elastically return and thus causing them to cyclically move towards and away from the body 1 . The resultant of these movements is an action of the wings on the liquid medium in which the device is immersed so as to generate thrust forces on the device.

The system can operate both in a repulsion mode, when a magnetic pole of the magnetised portion of the wings faces the same pole of the magnet on the rotor, and in an attraction mode, when a magnetic pole of the magnetised portion of the wings faces the opposite pole of the magnet on the rotor. Of course, it is possible for there to be other hybrid arrangements obtained by mixing the two aforementioned configurations, according to the use for which the device is intended.

The magnetic portions of the wings can be obtained, in addition to housing permanent magnets therein, as described above, also by using magnetic or magnetisable microparticles dispersed in the structure of the wing, generally made from flexible polymeric material. The wings can, in any case, be made in many shapes, dimensions and materials, the shape and the geometry of the wings influencing both the force and the surface interacting with the liquid.

The number of revs of the motor modulates the movement of the wings. A variation of the configuration and of the number of magnets generates a different opening and closing movement, possibly of two wings for each revolution of the motor or all of them simultaneously. The number of wings, the number of magnets on the rotor, the elastic return, the magnetisation and the fixed points of the wings, with their variation, lead to different behaviours of the device.

Once the magnetisation direction has been set, if the number of magnets is equal to the number of wings, all the wings flex simultaneously. Otherwise, the movement of the free end of the wings can be set to carry out movements that are not synchronised.

In addition to using permanent magnets rotating around the longitudinal axis of the body of the housing 1 , a variable magnetic field on the magnetised portions of the wings can be achieved through a magnet support translating along the axis X with an alternating movement, or by using any other type of source of variable magnetic field, such as microcoils. The steering of the device according to the invention can be controlled by an external operator through deformable rudder means whose shape or configuration is controllable by low power signals. For example, the device can be equipped with a I PMC (Ionic Polymer Metal Composite) rudder. As known, I PMC is a electroactive polymer operating best in a water or liquid environment, which shows large deformation in the presence of low applied voltage. Deformation can be achieved by PWM (Pulse Width Modulation electric signals of low power (voltage of few tens of V and negligible current). The signals can be generated by an on board miniaturised electronic circuit. Equivalent materials, such as piezoelectric materials, can be used as an alternative.

The locomotion of the device can also be completely autonomous and guided by environmental stimuli that are capable of causing a variation of the movement towards the direction from which the stimuli are coming, or in the opposite direction. Advantageously, for such a purpose, the device is equipped with sensing means for detecting physiological and/or environmental variables and inertial sensing means as well as steering means that, when activated by said sensing means, can produce the required direction variation. In particular, the device can be equipped with means that are suitable for actively reacting to environmental stimuli or external agents and that, once these stimuli or agents are detected, can act as rudders themselves, possibly through actuating means, for example by modifying their configuration (for example of the wings or of the forward part of the housing) and thus creating a structural asymmetry such as to vary the direction of movement. Materials which are capable of varying their shape in response to environmental stimuli, either of the physical type, such as temperature, light, magnetic fields, electric fields, mechanical stimuli, or of the chemical type, such as pH, electrochemical stimuli, biological stimuli etc., are for example described in Liu & Urban, Prog Polym Sci 35 (2010) 3-23.

Advantageously, the electronic card for controlling the motor also comprises transmission and receiving means for exchanging data telemetrically, in particular for a wireless transmission of the detected physiological or environmental variables.

In the case of use for medical applications (for example for inspecting the stomach or the bladder), the device according to the invention can be equipped with drug delivery mechanisms and/or sample withdrawal means and relevant collecting chambers, as well as equipment for intrabody therapy. Such mechanisms can be activated mechanically, thermally, chemically or activated through magnetic fields.

The device according to the invention is fully scalable by using small size motors and wireless energy transfer systems. Magnetic reed switches or Hall effect sensors can be integrated in a miniaturised electronic card to turn the device on/off. In order to produce the wings and the housing, micromanufacturing techniques can advantageously be used.

The main advantage of the microrobotic device according to the present invention consists in the structural simplicity and in the extreme scalability of the actuation mechanism, which therefore makes it possible to have a very high miniaturisation of the locomotion module. Thanks to the fact that the internal magnets do not rotate around their own axis, but around the support axis, only one actuator is necessary to transmit the motion to all the internal magnets simultaneously by directly acting upon the support. In this way, the variable magnetic field is generated without requiring intermediate mechanisms (reducers, joints or internal elastic elements).

Another advantage is the use of magnetically actuated wings for generating the motion. The resulting bending is generated by a single series of properly oriented internal magnets. In this way it is possible to act upon the configuration of the wings, by replacing the magnetic material with ferromagnetic material, so as to operate in the attraction mode rather than in the repulsion mode.

The considerable variability of the behaviour can be obtained, moreover, by modifying the configuration of the mobile support or the geometry and the mechanical properties of the wings. In this way it is possible to design wing configurations with improved hydrodynamic characteristics or capable of adapting to physical characteristics of a predetermined fluid (adaptability to different Reynolds numbers).

The microrobotic device according to the present invention allows locomotion in inaccessible or dangerous environments, even in robot swarm configuration. The robot can indeed be used for swarm robotics applications: the interaction with set environmental stimuli can make it possible to identify poisonous material sources or pathogenic agents and, possibly, to carry out simple tasks. Thanks to the extremely simple structure, the device according to the invention potentially has a very low cost, which essentially depends upon the manufacture technology used and that, in any case, will be further reduced when being produced in series.