TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and to a method for generating drops, in particular under microgravity or no-gravity conditions. PRIOR ART

Systems for generating drops, mainly used in the field of scientific research, that act under conditions of gravity and exploit the earth's gravitational field to generate the drops are known in the prior art.

Generally speaking, these systems are not entirely satisfactory in terms of the reproducibility and control ' of the parameters of the drops that are generated, and also have the main drawback of not being suitable for use under microgravity or even no-gravity conditions. OBJECT OF THE INVENTION

It is an object of the present invention to provide a drop generating device that overcomes the above drawbacks of the prior art and that is, in particular, capable of generating drops with characteristics in terms of size, trajectory and velocity that are perfectly controlled and that can also

(and especially) be used under microgravity or no- gravity conditions.

The present invention thus relates to a drop generating device and to a method for generating drops, in particular under microgravity or no-gravity conditions, as essentially defined by claims 1 and 12 respectively, and for further preferred aspects by the dependent claims.

According to the invention, inertial forces are used to generate and control the drops, instead of gravitational force.

In this way, thanks to the specific characteristics of the device and to the implementation steps of the method according to the invention, it is possible to produce drops the size, velocity and trajectory of which are perfectly controlled and reproducible, even under microgravity or no-gravity conditions. In particular, it is possible to generate drops with both zero velocity, and with a predefined fall velocity. The device according to the invention is also relatively simple and inexpensive to implement and easy to use .

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in further detail in the following non- limiting embodiments, with reference to the accompanying drawings in which:

- figure 1 is a schematic perspective view of a drop generating device, in particular under microgravity or no-gravity conditions, according to the invention, with a detail shown on an enlarged scale;

- figure 2 is a plan view from above of the device of figure 1, with some parts removed for the sake of clarity;

- figure 3 is a front view of the device of figure 1, with some parts removed for the sake of clarity.

PREFERRED EMBODIMENT OF THE INVENTION

With reference to the accompanying drawings, a device 1 for generating drops, in particular under microgravity or no-gravity conditions, comprises a guide 2, a carriage 3 movable back and forth along the guide

2, a needle 4 carried integrally by the carriage 3, a feed system 5 that feeds liquid to the needle 4, a movement system 6 which moves the carriage 3 and a control system 7 that controls the operation of the device 1 and the drop release point .

The guide 2 extends along a rectilinear translation axis A between two axially opposite ends 11, 12 and is integrally fixed to a supporting plate 8, for example made of hard chrome plated cold-rolled steel, by means of a bar 9 that is substantially parallel to the guide 2 and to the axis A.

The guide 2 is in particular a recirculating ball guide on which a sliding block 13 is mounted (figure 3) integrally fixed to the carriage 3; the sliding block 13 and the carriage 3 are axially slidingly coupled to the guide 2; the carriage 3 is thus axially slidable back and forth parallel to the axis A.

The carriage 3 comprises a substantially L- shaped bracket-type body 30 having an upper plate 31, which inferiorly carries the sliding block 13, and a lateral portion 32 arranged along a side of the guide 2. The carriage 3 is movable along the guide 2 between two opposite positions, located respectively at the ends 11, 12 of the guide and defining, respectively, a start-of- travel position and an end-of-travel position of the carriage 3.

The needle 4 is carried by a support 14 fixed to the carriage 3 and in particular above the plate 31; the needle ,4 is a capillary needle, preferably having a round cross-section, and extends along an axis B substantially parallel to the guide 2 (and thus to the axis A) ; the needle 4 has a free end 15 which terminates in a tip 16 through which the liquid contained in the needle 4 is supplied in drops,- the tip 16 has a front edge 17 substantially flat and orthogonal to the axis B. The needle 4 is connected via a duct 18 to the feed system 5, which comprises a reservoir 19 and a pump 20 (only schematically illustrated in figure 1) which draws in liquid at a controlled flow rate from the reservoir 19 and feeds it to the needle 4. Advantageously, the pump 20 is a micro piezoelectric pump or a peristaltic pump with a large number of rotors (for example 12 rotors), controlled by the control system 7. The pump 20 can also be of a different type, or can be replaced with a different flow control device (for example a syringe, etc) .

Optionally, a pressure impulse generator 21 can be arranged along the duct 18 downstream of the pump 20 to apply controlled pressure impulses to the flow of liquid fed by the pump 20 to the needle 4.

The movement system 6 comprises a motor or other actuator 23 apt to move the carriage 3 along the axis A; in the preferred embodiment that is shown, the actuator 23 consists of a linear motor extending along an axis M parallel to the axis A of the guide 2 and apt to move the carriage 3 alternately back and forth along the axis A. In particular, the motor 23 is a linear magnetic motor and specifically a brushless gearless motor; the motor 23 comprises a magnetic stator track 24 arranged parallel to the guide 2 and extending along the axis M; and a coil assembly 25 movable along the track 24 and fixed integrally to the carriage 3 and driving the carriage 3.

The track 24 is in particular a substantially U- shaped magnetic multi-pole track provided with magnets (for example rare-earth magnets) with alternating polarity, fixed to the supporting plate 8.

The coil assembly 25 comprises a slide portion 26, housed inside the track 24, and a drive portion 27 that extends from the slide portion 26 to the outside of the track 24 and is integrally connected to the carriage 3 ; the coil assembly 25 is centred with respect to the track 24 by means of bearings 28, in particular air bearings, for example carried by the guide 2 or by the bar ^' 9. Advantageously, the coil assembly 25 comprises a winding with a three-phase ironless core that eliminates the magnetic attraction force between the coil assembly 25 and the track 24.

Merely by way of example, the motor 23 is capable of moving the carriage 3 with accelerations of between approx. Ig and approx. 5g over a stroke of between approx. 200 mm and approx. 500 mm and preferably of approx . 300 mm.

The movement system 6 and the feed system 5 are connected to the control system 7 which controls the operation of the device 1.

In particular, the control system 7 comprises a control unit 34 (processor) connected to the pump 20 and to the motor 23, and to a position sensor 35, for example a high-resolution (approx. 20 micron) optic controller, arranged along the guide 2 for example in proximity to the end 12, and to an accelerometer 36, for example a capacitive accelerometer, mounted on the carriage 3, with a resolution of 140 micro-g. The control unit 34 acts on the pump 20 to control the flow of liquid fed by the feed system 5 to the needle 4; and acts on the motor 23 to control the motion of the carriage 3, by assigning a specific speed and acceleration profile to the carriage 3, and thus to the needle 4.

The device 1 operates, by implementing the method according to the invention, in the following way.

The user sets the operating parameters of the device 1, in particular the flow rate of the liquid fed to the needle 4 and the speed and acceleration profiles assigned to the carriage 3, via the control unit 34.

In particular, the control system 7 activates the feed system 5 to feed liquid to the needle 4 at a controlled flow rate, in order to form single drops of a predefined size at the tip 16 of the needle 4; the size of the drops essentially depends on the flow rate of the liquid through the needle 4, which must therefore be accurately controlled; this is possible, specifically, due to the presence of the control system 7 and the use of a suitable pump 20 (in particular, as stated above, a micro piezoelectric pump or a peristaltic pump) , capable of generating a liquid flow rate of between 0.5 and 3 ml/min (the typical operating interval of the device 1) . The control system 7 also activates the movement system 6 that moves the carriage 3 along the guide 2 in such a way to alternately give controlled accelerations and decelerations to the carriage 3 and create an inertial force that causes single drops to be released from the needle 4.

The carriage 3 moves cyclically translating alternately back and forth along a direction of translation, defined by the axis A of the guide 2, between the start-of -travel position (in which the needle 4 is filled with liquid) and an end-of-travel position, in which the drops are released from the needle 4.

The carriage 3 is moved so as to achieve relatively high accelerations and decelerations (of more than Ig and generally several g) and thus generate the force required to extract the drops from the needle 4. The drops detach from the tip 16 of the needle 4 by inertia caused by the motion of the carriage 3 and specifically by the inversion of the translatory motion of the carriage 3. The inertial forces generated by the controlled motion of the carriage 3 are sufficient to cause the drops to be released under perfectly controlled conditions of velocity and acceleration. Optionally, the timing of the release (and thus the residual velocity) of the drops from the needle 4 can be further controlled by means of a pressure impulse generated by the generator 21, also controlled by the control system 7. This option is particularly advantageous for generating arrays of drops .

The device 1 is preferably used with closed- loop acceleration control, via a signal supplied by the sensor 35. The real acceleration of the carriage 3 is measured by the accelerometer 36. It is understood that modifications and variations can be implemented to the embodiment described herein without departing from the scope of the invention as set forth in the claims. Firstly, it is clear that while reference is made to micro-gravity or no-gravity conditions, the device and method according to the invention can be used under other conditions .

An important aspect of the invention is the possibility of controlling the operation of the device 1 so that drops can be emitted at extremely low or even zero release rates .

Moreover, although in the non- limiting example to which reference is made herein the carriage 3 is moved by a linear motor 23, different movement systems 6 can be used to move the carriage 3 , for example mechanical systems (such as pre-loaded springs) or hydraulic systems, for example using compressed air.

In any case, the movement system 6 is apt to make the carriage 3 accelerate according to controlled speed and acceleration profiles, and to make the carriage 3 decelerate to generate an inertial force that suffices to cause the drop to be released from the tip 16 of the needle 4. The carriage 3 can thus be driven by actuators other than a linear motor, for example pre-loaded elastic members (springs) that first push the carriage 3 and then pull it back, thus generating the inertial force required for the drop to be released.

The drop can also be released, for example, by- making the carriage 3 collide with a limit stop set at the end-of-travel position, or at another appropriate point . So, more in general, the movement system 6 comprises an actuator 23 connected to the carriage 3 and apt to move the carriage 3 along the axis A and to give a controlled acceleration to the carriage 3 , and a stopping or slowing device acting on the carriage 3 and apt to interrupt or slow the travel of the carriage 3 thus generating the inertial force that causes the drop to be released (this device could be the actuator 23, as in the case of the linear motor described above, or another device) .