Patent Application
20130167940
The present invention relates to apparatus and methods for pressure regulation.
Inkjet printing heads dispense droplets of ink or other fluid material (for example liquids, suspensions, gels) via nozzles. The material to be dispensed is selectively discharged from an inkjet printing head nozzle or plurality of nozzles when an electric pulse is directed to the respective nozzle or nozzles. To prevent gravitational leakage, the printing head is maintained under a moderate sub-atmospheric pressure (vacuum) compared to the surrounding atmosphere, which is sufficient to keep the material from gravitationally dripping out of the nozzles.
The sub-atmospheric pressure needs to be continuously and precisely maintained within a predefined narrow range, because insufficient vacuum may lead to leakage while excessive vacuum might interfere with the operation of the discharge mechanism. The desired vacuum may depend on the design of the printing head, the specific gravity of the material being dispensed, and the height of the material above the nozzle level. An exemplary representative value of the sub-atmospheric pressure employed may be about −60 mm water pressure.
When material is dispensed from the printing head, the vacuum within the reservoir of material feeding the head increases, whereas when material is fed into the reservoir, the vacuum drops. For maintaining the vacuum at the desired level, a vacuum pump is customarily used to draw air out of the reservoir to reduce the pressure within, whereas a leak orifice inlet allows air to flow into the reservoir when the pressure inside the reservoir of material is too low. The electrical power supplied to the pump is controlled so as to ensure that a desired vacuum level is maintained.
Sub-atmospheric pressure is applied to prevent leakage, even when the printing device is inoperative. The mechanism described above for maintaining the vacuum thus requires uninterrupted operation of the vacuum pump at all times, which consumes energy and reduces the effective life of the pump.
There is thus provided, in accordance with embodiments of the present invention, a system for maintaining a desired pressure difference between a first pressure within a chamber and a reference pressure at a reference space. The system may include a peristaltic pump located along a duct that connects the chamber with the reference space. The system may further include a pressure sensor for monitoring an actual pressure difference between the first pressure within the chamber and the reference pressure at the reference space. The system may also include a controller for receiving a signal from the pressure sensor for determining the actual pressure difference from the pressure sensor and for operating the peristaltic pump, in accordance with the actual pressure difference and the desired pressure difference, to increase, decrease or leave unchanged the pressure within the chamber so as to maintain the actual pressure difference within predetermined proximity to the desired pressure difference.
In some embodiments of the present invention the reference space may be ambient atmosphere.
In some embodiments of the present invention the chamber forms part of a printing block of a printer.
In accordance with embodiments of the present invention the chamber may be within a material reservoir of the printing block.
In some embodiments of the present invention the controller may be designed to cause the peristaltic pump to operate when the measured pressure difference exceeds a predetermined pressure difference range.
In some embodiments of the present invention the predetermined pressure difference range may be a modifiable parameter of the system.
In accordance with some embodiments of the present invention there is provided a method for maintaining a desired pressure difference between a first pressure within a chamber and a reference pressure at a reference space. The method may include providing a peristaltic pump located along a duct that connects the chamber with the reference space and a controller. The method may also include monitoring an actual pressure difference between the first pressure within the chamber and the reference pressure at the reference space using a pressure sensor. The method may further include using the controller, receiving a signal from the pressure sensor for determining the actual pressure difference from the pressure sensor and operating the peristaltic pump, in accordance with the actual pressure difference and the desired pressure difference, to increase, decrease or leave unchanged the pressure within the chamber so as to maintain the actual pressure difference within predetermined proximity to the desired pressure difference.
The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:
According to embodiments of the present invention, an inkjet printer may be equipped with one or more printing heads. Each of the printing heads may include or be connected via valves or other means to a container, e.g. reservoir containing the fluid material to be dispensed and one or more print nozzles for dispensing the material upon electric actuation. One or more pressure sensors may be provided for sensing the relative pressure above the liquid material level, e.g. air in the reservoir, above the liquid level, and a peristaltic pump may be provided for regulating the pressure as described below.
Reference is made to
An inkjet printing block 140A may include material reservoir 150R for retaining a liquid material, such as ink, wax and/or a curable polymer (e.g. in printers for printing three-dimensional objects, such as, for example, described in U.S. Pat. Nos. 7,658,976, 7,725,209, 7,991,498, all incorporated herein by reference) and a print head 150H that includes one or more print nozzles 150N for dispensing the material.
Material reservoir 150R may be designed to supply liquid material to print head 150H as needed, to compensate for, i.e. replace quantities of material dispensed via the print nozzles 150N. The wavy line within material reservoir 150R symbolically represents separation between the material (below the line) and air (above the line), i.e. the liquid level within the reservoir. To prevent gravitational leakage from print nozzles 150N, a certain vacuum level relative to the surrounding atmosphere 120, for example −60 mm water pressure, may be continually maintained within material reservoir 150R. In practice, the mechanisms for the maintenance of the pressure difference may afford a tolerance of for example ±5%. In another example, the mechanisms for the maintenance of the pressure difference may afford a tolerance of ±5 mm water pressure.
In order to maintain the required vacuum level, a peristaltic pump 110 may be placed between material reservoir 150R and atmosphere 120, the peristaltic pump located along duct 124 connecting material reservoir 150R with atmosphere 120. When peristaltic pump 110 revolves in the direction indicated by A (counter-clockwise, in this example), it moves air from material reservoir 150R of inkjet printing block 140A to atmosphere 120, thereby increasing the vacuum within material reservoir 150R. Similarly, revolving peristaltic pump 110 in the opposite (B) direction (that is clockwise, in this example) moves air from atmosphere 120 into material reservoir 150R, thereby increasing the pressure within material reservoir 150R, i.e. reducing the vacuum there.
There are five mechanisms that regulate the current pressure above the material level in the material reservoir 150R (see also blocks 209-225 in
Controller 114 receives a current pressure data from pressure sensor 130, which represents the pressure difference between the atmospheric pressure and the pressure within pipe 124, which, in turn, corresponds to the pressure above the liquid material level within material reservoir 150R, and actuates peristaltic pump 110 to revolve as necessary to maintain a predetermined level of vacuum within material reservoir 150R. If the current pressure is sufficiently close to the predetermined level, then controller 114 keeps peristaltic pump 110 still, actually functioning as a closed valve.
Reference is now made to
Thus, apparatus 100A includes chamber 140 in which it is desired to maintain a predetermined pressure level. Pressure variator 150 may be any device or combination of devices that may add air or another material into chamber 140 and may remove air or another material from chamber 140. To prevent or compensate for pressure fluctuations within chamber 140 caused by operation of pressure variator 150, peristaltic pump 110 may be placed between chamber 140 and atmosphere 120, and operate under the control of controller 114. Pressure sensor 130 may be used to measure the pressure difference between the inside of chamber 140 and the outside atmosphere 120, and controller 114 may actuate peristaltic pump 110 so as to maintain a predetermined pressure within chamber 140, in a manner similar to the manner described hereinabove with reference to
The relative pressure may be measured by a pressure sensor and reported to a controller. The method may further include comparing 209 the pressure difference between the actual relative pressure and a desired relative pressure or pressure range. The comparison may be carried out, for example, by a controller that receives pressure measurements from a pressure sensor. If the measured relative pressure, i.e. actual relative pressure is lower than the desired relative pressure, or a desired pressure difference range, the peristaltic pump may be operated 215 to add air to the chamber, thereby increasing the actual relative pressure (reducing the vacuum) toward the desired level. If the measured actual relative pressure is higher than the desired relative pressure, or a desired pressure difference range, then the peristaltic pump may be operated 225 to remove air from the chamber, thereby reducing the actual relative pressure (increasing the vacuum) within the chamber toward the desired level. If the measured actual relative pressure is found to be equal or sufficiently close (within a predetermined pressure difference range) to the desired relative pressure, then the peristaltic pump is kept 219 still, thereby effectively causing the peristaltic pump to act as a valve that blocks passage of air between the ambient atmosphere and the inside of the chamber.
The pressure difference range may be a modifiable parameter of the apparatus, so as to allow setting it by a user, thereby affecting the sensibility of the apparatus to changes in the pressure difference.
Examples of determination of desired pressure levels:
Liquid level above nozzle level=50-60 mm; Gravity of liquid material=1; the desired relative pressure: about −60 mm water pressure
Liquid level above nozzle level: =50-60 mm; Gravity of liquid material=3; the desired relative pressure: about −160 mm water pressure
While the invention has been described with respect to a limited number of embodiments, it will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein. Rather the scope of the present invention includes both combinations and sub-combinations of the various features described herein, as well as variations and modifications which would occur to persons skilled in the art upon reading the specification and which are not in the prior art.
