Abstract:
A dispensing unit for a fluid dispensing machine comprises at least an inlet duct and an outlet duct for fluid products, connected to a variable-volume pumping chamber comprising at least one flexible wall. Two non return valves mounted in counter-phase are located in the inlet and outlet ducts, respectively. The pumping chamber is coupled to actuator means comprising a stepper motor, a screw-nut screw unit and a carriage. The carriage moves the pumping chamber from a zero position in which the chamber has a maximum volume to an upper limit in which the chamber has a minimum volume. An optic sensor defines the zero point of the pumping chamber so as to guarantee precision and repeatability of the dispensing operations.

Description:
TECHNICAL FIELD 
     The present invention relates to the field of dispensing machines intended to dispense and/or meter more or less viscous fluid products, such as for example paints, colorants, inks, and the like. 
     BACKGROUND ART 
     Prior art in the above sector comprises dispensing machines that run according to various operating principles. One fairly widespread type of known machine comprises multiple reservoirs for colorant fluids, connected to a dispensing circuit. Each fluid product is drawn from its respective reservoir by a positive-displacement pump and delivered to a corresponding three-way two-position distributing valve. When the valve is in an inactive position, the fluid is returned to its respective reservoir through a recirculation duct. When it is necessary to dispense a pre-set amount of fluid, the valve is set to an active position so as to deliver the fluid from the reservoir to a dispensing nozzle. This type of machine provides excellent results in terms of precision repeatability and reliability Of results over time. However, the use of a pump and solenoid valve for each reservoir of fluid product raises the overall cost of the machine, in terms of both manufacture and servicing. Another known type of dispensing machine for fluid products, especially colorant fluids, comprises a series of reservoirs connected to or integrated with syringe-type dispensing pumps, comprising plungers axially movable inside respective cylinders, the pumps being usually arranged around the circumference of a rotating drum. To distribute a pre-set amount of fluid product into a container, it is necessary to rotate the drum until the appropriate syringe is aligned with the container. Generally, therefore, in machines of this known type it is impossible to dispense multiple fluid products simultaneously into the same container, which leads to low productivity for machines of this known type. Various solutions have been proposed to overcome the above problem all fairly complicated and costly to manufacture and service. In addition, one intrinsic problem with known syringe-type machines lies in the difficulty of providing sufficient sliding seals between the plungers and cylinders to ensure good precision and repeatability over time in dispensing and metering. Also, use of these machines with aggressive or abrasive fluids leads to rapid wear on the sliding seals and thus a decline in the machine performance, which can only partly be overcome by constant servicing, which heavily increases the running costs of the machine. 
     DISCLOSURE OF THE INVENTION 
     The object of the present invention is to overcome the above problems with the prior art by providing a dispensing machine to dispense and/or meter fluid products which is easy and economical to manufacture and service, and which provides high precision and reliability over time, even when using aggressive, corrosive or abrasive fluid products. Another object of the present invention is to provide a machine that is compact in size with satisfactory productivity performance, especially—but not exclusively—when dispensing limited amounts of fluid products. A further object of the present invention is to provide a machine comprising a plurality of independent dispensing units which are easy to manufacture and install on the machine and which can be quickly replaced if needed, even by unskilled personnel, for example even the machine user. In order to achieve the above objects, the present invention relates to a dispensing unit having the characteristics described below. The invention also relates to a dispensing machine to dispense and/or meter fluid products, comprising a plurality of dispensing units of the above type. 
     According to a particular feature of the present invention, the dispensing unit comprises a pumping chamber with flexible walls, in particular but not exclusively bellows-like walls. In one particular embodiment, the pumping chamber is activated by a linear actuator in order to provide a linear proportion between the actuator stroke and the amount of product dispensed. According to a further particular feature, the linear actuator comprises a stepper motor to provide a linear proportion between the number of motor steps and the amount of fluid dispensed. Another special feature lies in the fact that, with the dispensing unit of the present invention, the pressure in the delivery duct to the dispensing nozzle drops immediately as soon as dispensing is interrupted, which prevents dripping and droplets at the nozzle. 
     According to another feature of the invention, the dispensing unit is set to filling position at the end of each dispensing, making the dispensing unit immediately available for the next delivery. 
     Yet another feature of the invention is that the dispensing unit comprises an optic limit sensor, which defines the zero point for the pumping unit. This feature makes it possible to achieve high repeatability of the dispensing process of a fluid product by the dispensing unit. 
     Another feature of the dispensing unit lies in the fact that the intake and dispensing strokes may take place at different speeds, to improve the machine productivity by reducing the time needed to refill the pumping chamber, yet without sacrificing precision during the dispensing phase. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages shall become apparent from the description below of one preferred embodiment, with reference to the enclosed figures, provided solely as nonlimiting examples, wherein: 
     FIG. 1 is a longitudinal schematic cross-section of a pair of dispensing units of the present invention, mounted inside a body of a dispensing machine, 
     FIG. 2 is an enlarged longitudinal cross-section of the pumping unit of the present invention, 
     FIG. 3 is a diagram of the control system for a dispensing machine of the present invention, especially suited to sequential dispensing of products, and 
     FIG. 4 is a diagram similar to FIG. 3, illustrating a control system especially suited to simultaneous dispensing of products. 
    
    
     DETAILED DESCRIPTION 
     With reference now to the figures, a dispensing machine to dispense and/or meter fluid products comprises a body  10 , at the front of which is located at least one nozzle or group of dispensing nozzles  11 , of a generally known type, reached by dispensing ducts  12  that serve to convey preset amounts of fluid products into one or more cans C, simultaneously or sequentially. The dispensing machine body may take on different overall shapes and configurations, primarily dictated by the transport or handling needs of the cans C, as well as considerations of ergonomics and appearance, which are not especially relevant to the present invention. For these reasons the overall structure of the machine is not described in detail in the remainder of this description. 
     Inside the dispenser body  10 , dispensing units  13  are located, each of which comprises a reservoir  14  for a fluid product, connecting to a pumping unit  15 , which in turn is connected to its respective dispensing duct  12  leading outside at the nozzle or group of nozzles  11 . A filter  16  is preferably inserted between the reservoir  14  and the corresponding pumping unit  15 . A stirring member  17 , of a generally known type—for instance, a rotary blade type as illustrated in FIG. 1, activated by a motor unit  18  attached at the lower end of the reservoir itself—may be mounted inside the reservoir  14 . 
     The generic pumping unit  15 , illustrated in greater detail in FIG. 2, comprises a base support  19  beneath which is a stepper motor  20 , whose motor shaft  21  extends into a cavity  22  provided in the base support  19 . The motor shaft  21  is connected to an actuator member  23 , rotatably mounted in the base support and supported therein by a pair of axial bearings  24 . A nut screw  25  is axially located in the actuator member  23 , into which is screwed the threaded end  26  of a drive shaft  27  acting as a drive screw. The screw-nut screw coupling is preferably of the irreversible type. The drive shaft  27  is fixed to a carriage  28  that slides along vertical guide bars  29  fixed to the base support  19 , upon which a position sensor  40  is also mounted, the function of which shall become clear hereinbelow. 
     The lower base of a bellows-like pumping chamber  30  is fixed to the carriage  28 ; the internal cavity  30   a  of the chamber communicates with a manifold  31  provided inside an upper cross-beam  32 , fixed to the top end of the guide bars  29 . The manifold  31  in turn communicates with an inlet  33  and an outlet  34 , which communicate with the reservoir  14  and the dispensing duct  12 , respectively, with the interposition of two respective non-return valves  35  and  36 . In detail, the non-return valves each comprise a spherical shutter  37  that urges against, a circular valve seat  38  thanks to the action of a resilient element  39 , preferably a pre-set helical spring. 
     The stepper motor may be controlled by an electronic control system  45  (shown schematically in FIG. 4) mounted on the dispensing unit  13 , which may also control the motor unit  18  of the stirring member  17 . In the embodiment illustrated in the diagram in FIG. 4, the control systems  45  communicate with a central processing unit  46 , preferably installed on the machine and capable of sending information to activate the control system  45  of the appropriate dispensing unit  13  following a dispensing request for a preset amount of one or more fluid products. In particular, the central processing unit  46  acts as the machine/user interface and is connected by any known data transmission system to a circuit block  47 , responsible for controlling and managing the members of the dispensing machine. The circuit block  47  is connected in known ways to the machine resources, such as a dispensing nozzle humidifier device  48 , an actuator  49  for a shelf to adjust the container height, or even a sensor system  50  to detect the presence of the container in the dispensing compartment of the machine, as well as others. In the case of FIG. 4, the circuit block  47  connects via a data network connection  51  with the control systems  45  placed on each dispensing unit  13 . In this case, it is possible to simultaneously activate two or more dispensing units  13 , and thus simultaneously dispense two or more products. 
     In another embodiment, shown schematically in FIG. 3, the circuit block  47  is connected to an I/O card  52  that directly controls, without the interposition of the control systems  45 , the dispensing units  13  and receives information signals from each unit, for example the signals emitted by each position sensor  40 . This solution makes it possible to manufacture a dispensing machine decidedly more economical than the one shown in FIG. 4, as it is not necessary to equip each dispensing unit  13  with its own independent control logic. Although the control system in FIG. 3 does not allow for the simultaneous dispensing of products, the precision and repeatability of the dispensing suffer no decline, as they are determined by the features of each dispensing unit  13 . 
     During periods of inactivity, when no product dispensing is in progress, all dispensing units on the machine are in a resting position, where the bellows-like pumping chambers  30  are open to their maximum extension and completely filled with fluid product. In these situations, the carriages  28  are positioned at the lower end of their stroke as detected by the position sensors  40 . The electronic systems installed on the machine are set up to process information regarding amounts of fluid products to be distributed in terms of either volume or weight, and translate them by means of conversion tables into information on the number of cycles and fractions of cycles needed in order for the pumping chamber  30  to transfer the desired amount of fluid product to the corresponding outlet duct  12 . This conversion is simplified by the fact that the ratio between the volume of product transferred to the outlet following a compression of the bellows  30  is essentially directly proportional to the axial movement of the drive shaft  27 , and thus the number of steps of the stepper motor  20 . 
     When the central processing system  46  sends dispensing information to a specific pumping unit  15  via the circuit block  47 , the local electronic control system  45  or the I/O board  46  activates the stepper motor  20  to control the movement of the carriage  28 , and thus the compression of the bellows-like pumping chamber  30 . Since the cavity  30   a  of the pumping chamber is already full of fluid product, the dispensing unit is immediately ready to dispense as soon as it receives the activating information from the central processing unit. 
     If the volume of the fluid product to be dispensed is less than the displacement of the bellows-like pumping chamber  30 , the stepper motor  20  is controlled in one rotation direction for a number of steps sufficient to reduce the volume of the pumping chamber by an amount equal to the volume of product to be distributed. Since the fluid products to be dispensed are essentially non-compressible, the pressure generated inside the chamber  30   a  as soon as the carriage  28  is raised to compress the bellows  30  is enough to overcome the resistance of the spring  39  of the non-return valve  36 , thereby opening it, and thus causing fluid product to leave the dispensing duct  12 . This duct is normally full of product and is preferably short to reduce the effects of load loss on the precision and linearity of the dispensing unit. When dispensing is complete, the stepper motor  20  is controlled in the opposite direction until the sensor  40  signals that the carriage  28  has reached the lower end of its stroke. As soon as the motor  20  reverses its direction, the pressure inside the chamber  30   a  drops, causing the non-return valve  36  to close immediately. This also causes the pressure to drop in the dispensing duct  12 , and, due to the slight shift by the shutter  37 , probably also creates a slight vacuum in the duct  12  sufficient to prevent the formation of drops or leaks of fluid product at the nozzle  11 . During the return stroke of the carriage  28  toward the lower end of its stroke, the volume of the chamber  30   a  of the bellows  30  increases, thereby drawing fluid product from the reservoir  14  through the non-return valve  35  which opens. As shown in FIG. 1, the reservoir  14  is preferably located above the corresponding pumping unit  15  and is connected to it by an essentially vertical duct with a fairly wide cross-section. All of this facilitates penetration of the fluid product into the chamber  30   a  when the carriage  28  is lowered, without the risk of cavitation. The fact that it is so easy to draw product from the reservoir  14  makes it possible to control the return stroke of the carriage  28  at a greater speed than the dispensing stroke. 
     This feature is specially advantageous when the amount of product to be dispensed is greater than the displacement of the bellows. In this case, the electronic control system controls the stepper motor  20  so that it completes one or more full dispensing cycles, each of which consists of a complete stroke by the carriage  28  upwards and a return downward stoke to the lower limit position detected by the position sensor  40 . In order to deliver the desired amount of fluid product, the last dispensing stroke of the carriage  28  shall usually be a partial stroke, followed by the return of the carriage  28  to the lower end of its stroke, in resting position. The fact that the return strokes of the carriage  28 , during which the nozzle  11  has stopped dispensing product to allow the chamber  30   a  of the accordion  30  to refill, take place at a higher speed than the delivery strokes reduces refilling times and thus increases the overall productivity of the dispensing machine. 
     The presence of the position sensor  40  makes it possible to easily implement an important control function of the proper operation of the dispensing unit, and consequently a procedure to correct any malfunctions. Indeed, it is necessary simply to count the number of motor steps needed to return the carriage to home position, or the lower end of its stroke—indicated by the position sensor—and compare it to the number of steps taken by the motor to carry out the carriage forward stroke. This immediately checks for any operating errors if the two numbers do not match. In this case, the control system can generate an error signal and indicate the malfunction to the user. In addition, if the number of steps in the dispensing stroke is lower than in the return stroke, the processing system can automatically activate the step motor again for the number of steps equal to the difference found, to deliver the missing amount of product and thus complete the dispensing operation, which would otherwise be defective. 
     To increase the productivity of the machine, it is also possible to parallel control several dispensing units, as shown in the example of the diagram in FIG. 4, so that several fluid products may be dispensed simultaneously into the same container C through a shared set of nozzles  11 . This need is especially felt in the-paint, enamel, etc. manufacturing industry, where it is normal to deliver preset amounts of various colorant products into a container C to obtain a finished product having the desired color shade. 
     The fact that the screw-nut screw connection which acts as a linear actuator between the stepper motor  20  and the carriage  28  is irreversible allows the carriage  28  to remain in its position even in the event of a temporary, accidental electrical power loss. In other words, the type of screw-nut screw used does not allow the carriage to move except after the stepper motor has been activated in one rotation direction or the other. Each dispensing unit  13  is independent and may easily be replaced even by unskilled personnel in the event of a breakdown, since one must simply connect the electrical power and communication connectors of the dispensing duct  12 . The bellows-like pumping chamber  30  may be made using materials that resisist aggression by fluid products, for example fluoride-based polymers. The absence of sliding seals ensures high reliability even in the presence of abrasive fluids. Of course, the geometry of the pumping chamber may vary from the example shown: for example, it may comprise a different type of variable-volume chamber such as one with flexible walls, or a diaphragm, or similar solutions. In addition, the same carriage may control more than one pumping chamber. 
     Of course, the principle of the invention remaining the same, the embodiments and development details may vary widely from those described and illustrated without exceeding the extent of the present invention.