EJECTOR-TYPE VACUUM PUMP ASSEMBLY HAVING STABILISED MEMBRANE FLOW VALVE, AND A METHOD OF CONTROLLING A VACUUM LEVEL IN A VACUUM CHAMBER OF AN EJECTOR-TYPE VACUUM PUMP OF THE ASSEMBLY

Abstract

Described is an ejector-type vacuum pump assembly that includes a stabilizing membrane flow valve, wherein a pilot flow of pressurized air is used to regulate a main flow of pressurized air for driving an ejector-type vacuum pump is disclosed. The pilot flow is led to a downstream side of the membrane flow valve and is fed to the ejector of the ejector-type vacuum pump along with the main flow of pressurised air. The ejector-type vacuum pump assembly is primarily intended for automated gripping operations using a suction gripper. Also disclosed is a method of controlling a vacuum level in a vacuum chamber of an ejector-type vacuum pump in an ejector-type vacuum pump assembly as described herein.

Claims

1. An ejector-type vacuum pump assembly, said assembly comprising: an ejector-type vacuum pump comprising a pressure chamber, an ejector nozzle, a vacuum chamber, and an exhaust, the ejector nozzle fluidly connecting the vacuum chamber with the pressure chamber; an inlet for pressurized air; a first flow-control valve comprising a valve chamber, the first flow-control valve being configured to control a flow of pressurized air from the valve chamber to the pressure chamber; and, a pressure sensor configured to sense a pressure (P) in the ejector-type vacuum pump assembly, wherein that the pressure sensor is located in the vacuum chamber; that the valve chamber is fluidly connected to the inlet for pressurized air; that the valve chamber comprises a bottom having an opening, a wall having an orifice fluidly connecting the valve chamber with the pressure chamber; that, in the valve chamber of the first flow-control valve , a flexible, collapsible, cylindrical membrane is housed, the flexible, collapsible, cylindrical membrane being configured to seal against the bottom and/or to the wall, and, in a relaxed, un-collapsed state of the collapsible, flexible cylindrical membrane, to seal the orifice , the first flow-control valve further comprising an inner rigid flow chamber comprising, in an upstream end thereof, a flow restriction fluidly connecting the valve chamber with the rigid inner flow chamber, and, in a downstream end thereof, an outlet fluidly connected to the opening, the rigid inner flow chamber having in a side wall an orifice fluidly connecting the inner flow chamber with an inner volume enveloped by the collapsible, cylindrical, flexible membrane and the bottom, the upstream end of the rigid flow chamber being sealingly connected to an opening in an upstream end of the collapsible, cylindrical, flexible membrane; and, in additionally comprising: a second flow-control valve configured to regulate a pilot flow of pressurized air from the inner flow chamber into the pressure chamber.

2. The ejector-type vacuum pump assembly of claim 1, wherein the pressure sensor is additionally configured to send a pressure control signal (S1) proportional to the pressure (P) sensed; and wherein the ejector-type vacuum pump assembly additionally comprises: a controller (CU) configured to receive a pressure control signal (S1) from the pressure sensor, to compare the pressure control signal (S1) received with a desired target pressure (P.sub.TARGET), to establish any existence of a pressure difference (P) between the pressure sensed (P) and a desired target pressure (P.sub.TARGET), and, in the case of an established existence of a pressure difference (P) between the pressure sensed (P) and the desired target pressure (P.sub.TARGET), to send a flow control actuation signal (S2) to the second flow-control valve corresponding to the sign (+/-) of the pressure difference (P) established between the pressure sensed (P) and the desired target pressure (P.sub.TARGET).

3. A method of controlling a vacuum level in a vacuum chamber of an ejector-type vacuum pump in an ejector-type vacuum pump assembly of claim 1, comprising the following steps: A supplying pressurized air to an ejector-type vacuum pump assembly; B monitoring a pressure (P) in a vacuum chamber of an ejector-type vacuum pump of the ejector-type vacuum pump assembly; and, C controlling a flow-control valve based on the pressure (P) monitored, thereby regulating a pilot flow of pressurized air through the flow-control valve; wherein a pressure differential between a reduced pressure produced by the pilot flow of pressurized air, and the pressure of the pressurized air being supplied to the ejector-type vacuum pump assembly in step A, regulates a flow of pressurized air driving the ejector-type vacuum pump.

4. The method of controlling a vacuum level in a vacuum chamber of an ejector-type vacuum pump in an ejector-type vacuum pump assembly of claim 3, wherein a control unit (CU) is used to maintain a desired target pressure in vacuum chamber, wherein step B includes sensing a pressure (P) in the vacuum chamber and sending a pressure control signal (S1) to the control unit (CU) proportional to the pressure (P) sensed in the in vacuum chamber, and wherein step C includes comparing the pressure control signal (S1) received with a desired target pressure (P.sub.TARGET), establishing any possible existence of a pressure difference (P) between the pressure sensed (P) and the desired target pressure (P.sub.TARGET), and, in the case of an established existence of a pressure difference (P) between the pressure sensed (P) and the desired target pressure (P.sub.TARGET), sending to the flow-control valve a flow control actuation signal (S2) corresponding to the sign (+/-) of the pressure difference (P) established between the pressure sensed (P) and the desired target pressure (P.sub.TARGET).

Description

BRIEF DESCRIPTION OF THE ATTACHED DRAWING

[0030] The Figure shows a cross-sectional view of an embodiment of an ejector-type vacuum pump assembly 10 according to the invention, wherein the first flow-control valve 200 has been integrated with an ejector-type vacuum pump 100.

DETAILED DESCRIPTION

[0031] The present disclosure uses a cylindrical servo-valve 200 capable of regulating a feed pressure to an ejector-type vacuum pump 100 via a re-useable bypass flow.

[0032] Accordingly, the valve with has a flow-capacity that can be controlled via a pilot airflow in order to supply an ejector-type vacuum pump 100 with a controlled feed pressure so as to be able to control the vacuum-level, i.e. the pressure, P in the ejector.

[0033] The side wall 245 of the inner rigid flow chamber 240 is rigid so as to maintain geometrical integrity of flow chamber 240, also at instances when a pressure differential over the wall is present. The flow chamber 240 is surrounded by the collapsible, cylindrical, flexible membrane 220. The flow chamber 240 is preferably tubular, and is preferably essentially concentric with the collapsible, cylindrical, flexible membrane 220.

[0034] When flow-control valve 300 is in a closed state and pressurized air is supplied to inlet 20, inner, rigid flow chamber 240 and valve chamber 210, the inner volume 280 of the collapsible, cylindrical, flexible membrane 220, being connected with inner, rigid flow chamber 240 via orifice 270 in the wall 245 of the inner rigid flow chamber 240, will be pressurized by the internal pressure building up in the inner rigid flow chamber 240. When the internal pressure in the inner rigid flow chamber 240 is equal to the feed pressure of the pressurized air entering inlet 20, opening 230 will be sealed off by the collapsible, cylindrical, flexible membrane 220, which is in its relaxed state, and therefore in contact with the wall 225 of the valve chamber 210. At this pressurized state, the pressures in the valve chamber 210, in the flow chamber 240, and in the inner volume 280 of the collapsible, cylindrical, flexible membrane 220, respectively, will be equal, and also equal to the pressure of the pressurized air being supplied to inlet 20.

[0035] Now, upon opening of flow-control valve 300 from the above closed state while pressurized air is supplied to inlet 20, a flow of air from the opening 257 in the downstream end of inner rigid flow chamber 240 will be established, and thereby, a pressure-drop over the restriction 260 will be created, causing the pressure in the flow chamber 240 to become smaller than the inlet pressure of the pressurized air being supplied to inlet 20.

[0036] The collapsible, cylindrical, flexible membrane 220 will collapse gradually due to the pressure-gradient between the inner volume 280 of the collapsible, cylindrical, flexible membrane 220 and the flow chamber 240, and thereby an airflow is created through orifice 230 from valve chamber 210 to the pressure chamber 110. The airflow from orifice 230 builds pressure in pressure chamber 110, which pressure in turn will limit the airflow through flow-control valve 300, and balance the collapsible, cylindrical, flexible membrane 220 and limit the airflow through orifice 230 through which pressurized air will be supplied to the pressure chamber 110 from the valve chamber 210.

[0037] The combined airflows from orifice 230 and from flow-control valve 300 are then expanded through the ejector-type vacuum pump 100 creating a reduced pressure in vacuum chamber 130. A conduit 405 fluidly connecting inner rigid flow chamber 240 with pressure chamber 110 is provided, along which conduit flow-control valve 300 is located.

[0038] By controlling the by-pass flow via the flow-control valve 300 the pressure in the pressure chamber 110 can then be controlled in a balanced manner due to the pressure-feedback provided via the by-pass connection from flow-control valve 300 to the pressure chamber 110. Increasing the flow exiting the flow chamber 240 by opening the flow-control valve 300 creates a larger pressure-drop between the pressure in the flow chamber 240 and the inlet pressure of the pressurized air being supplied to inlet 20, thereby allowing for the collapsible, cylindrical, flexible membrane 220 to collapse further, thereby opening a larger section of the orifice 230 through which pressurized air will be supplied to the pressure chamber 110 from the valve chamber 210. Depending on how the first flow-control valve 200 is housed in the body of the ejector-type vacuum pump 100, sealings 205 may be required for sealing off orifice 230 from ambient air, so that a flow of pressurized air exiting through orifice 230 from valve chamber 210 will be directed into the pressure chamber 110, such as in the embodiment shown in the Figure.

[0039] The purpose is to measure and feedback the vacuum-level created in vacuum chamber 130, and to control the vacuum level therein.

[0040] A multitude of orifices 230, all of which are fluidly connected to pressure chamber 110, are preferably included, which orifices are preferably distributed along the periphery of the wall 225 of the valve chamber 210. The orifices 230 are preferably located at a height of the wall 225 corresponding to a height of the collapsible, cylindrical, flexible membrane 220 just below a height where the upstream end 222 of the collapsible, cylindrical, flexible membrane 220 when in its relaxed state reaches and contacts the wall 225. The upstream end 222 is preferably rounded such as essentially hemispherical. It is believed that a relatively high positioning of the orifices 230 will serve to reduce the extent of flexing of the membrane along its height, and the degree of collapsing of the membrane required for opening the orifices, which in turn is believed to further enhance the stability of the inventive flow control.

[0041] The ejector-type vacuum pump assembly 10 can be used with one or more suction grippers, e.g suction cups or suction pads, fluidly connected to suction opening 105.

[0042] The flow-control valve 300 can for example be a manually operated needle valve, a stepper-motor controlled needle valve, a solenoid proportional valve, a linear directly operated solenoid valve, or a linear micro flow piezo-valve. For a close and simplified regulation of flow control valve 130, said valve is preferably a linear valve.

[0043] As will be understood from the present disclosure, the flow valve, pressure and flow control can be realized without any sliding elements, thereby avoiding all issues that potentially arise with friction and initial slip-stick. This creates the possibility to have a smooth regulation, without undesired step-changes due to friction. Moreover, the realization of the flow valve, pressure and flow control can be accomplished without strict requirements on tolerances.

[0044] In an embodiment, a controller is used to control the control flow-valve 300. The controller CU is preferably a PID controller. A regular PID control with vacuum-level in chamber 130 used as feedback and setpoint signal will require some initial tuning for stability and speed.

[0045] The CU, having received a pressure control signal S1 from the pressure sensor 150, compares said pressure control signal S1 received with a desired target pressure P TARGET, to establish a potential existence of a pressure difference P between the pressure sensed P and a desired target pressure P TARGET.

[0046] The pressure difference P can be established by subtraction of P TARGET from the pressure sensed P. In such case, an established positive pressure difference P represents a too high pressure in the vacuum chamber (i.e. a too low vacuum level), in which case the flow control actuation signal S2 from the CU will be to open the second flow-control valve 300. Conversely, an established negative pressure difference P represents a too low pressure in the vacuum chamber (i.e. a too high vacuum level), in which case the flow control actuation signal S2 from the CU will be to close the second flow-control valve 300.

[0047] Obviously, the pressure difference P could alternatively be established by subtraction of the pressure sensed P from the target pressure P TARGET.

[0048] The flow control actuation signal S2 is accordingly intended to reduce any pressure difference P established between P TARGET and the pressure sensed P by corresponding adaptation of the opening state of the second flow-control valve 300. The flow control actuation signal S2 could e.g. correspond to a pre-determined discrete step-wise alteration of the opening state of the valve, or could be proportional to the pressure difference P established between P TARGET and the pressure sensed P.

[0049] A user of the system can readily control the vacuum-level in vacuum chamber 130 of a process or handling application with high precision. This enables a significant potential for saving energy as compared to operating at full air-pressure, as well as for improving productivity by increasing the precision and limiting the variation in vacuum-level in a process. The present invention offers a huge potential in energy saving and cost for compressed air.

[0050] For example, in a handling application handling cardboard boxes, the cardboard quality will typically vary between suppliers and batches and even with environmental parameters such as humidity. This will require the handling application to be tuned to handle the worst cardboard on the worst day in order to maintain desired process stability. With the system disclosed herein, the system can be sized for the worst cardboard on the worst day, but tuned automatically for every handled box to only use as much compressed air as needed to create the vacuum-level required.

LIST OF REFERENCE NUMERALS USED

[0051] 10 ejector-type vacuum pump assembly

[0052] 20 inlet for pressurized air

[0053] 105 suction opening

[0054] 100 ejector-type vacuum pump

[0055] 110 pressure chamber

[0056] 120 ejector nozzle

[0057] 130 vacuum chamber

[0058] 140 exhaust

[0059] 150 pressure sensor

[0060] 200 first flow-control valve

[0061] 205 sealings

[0062] 210 valve chamber

[0063] 215 bottom of valve chamber

[0064] 217 opening in bottom of valve chamber

[0065] 220 collapsible, cylindrical, flexible membrane

[0066] 222 upstream end of collapsible, cylindrical, flexible membrane

[0067] 225 wall of valve chamber

[0068] 227 opening in upstream end of collapsible, cylindrical, flexible membrane

[0069] 230 orifice in wall of valve chamber

[0070] 240 inner rigid flow chamber

[0071] 245 side wall of inner rigid flow chamber

[0072] 250 upstream end of inner rigid flow chamber

[0073] 255 downstream end of inner rigid flow chamber

[0074] 257 opening in downstream end of inner rigid flow chamber

[0075] 260 flow restriction

[0076] 270 orifice in wall of inner rigid flow chamber

[0077] 280 inner volume of first flow-control valve

[0078] 300 second flow-control valve

[0079] 405 conduit fluidly connecting inner rigid flow chamber 240 with pressure chamber 110

[0080] P pressure in vacuum chamber 130

[0081] S1 pressure control signal proportional to pressure P

[0082] S2 flow control actuation signal

[0083] CU controller

[0084] P.sub.TARGET desired target pressure in vacuum chamber 130

[0085] P difference between the pressure P sensed and desired target pressure P.sub.TARGET