Pump start-up control

Abstract

A rotating vane vacuum pump (1) and a method for evacuating a vacuum chamber (2) are disclosed. The rotating vane vacuum pump comprises: an inlet (3) for connection to a vacuum chamber (2) and an outlet (4) for discharging fluid pumped by the vacuum pump; a rotor (6) and a motor (13) for driving the rotor. The pump has a venting channel (7) for venting one of the pumping chambers within the vacuum pump. The ventilation channel (7) has flow control means for controlling the flow through the ventilation channel. The flow control device is configured to allow flow through the vent passage upon activation of the pump and to impede flow through the vent passage in response to at least one of a predetermined time lapse, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from the sensor, the output from the sensor is indicative of operation of the vacuum pump.

Description

Technical Field

[0001] The field of the invention relates to vacuum pump starting and, in certain preferred embodiments, to reducing the torque required during pump starting. Background Art

[0002] When a vacuum pump is started, it may initially pump gas at a higher pressure (e.g., at atmospheric pressure), and this may require a much greater amount of torque than required during steady-state operation when the pressure is much lower. This is due to the additional fluid being displaced in the pump, which creates a significant drag in addition to the drag due to the inertia and static friction of the rotor.

[0003] This is a particular problem in some types of pumps, such as sliding vane rotary oil vacuum pumps, because in addition to the gas transfer, there is also the transport of oil used to seal the vanes at startup. The torque required to overcome these forces at startup creates an initial load on the pump motor that can be several times the load during normal steady-state operation. This can be a limiting factor when determining the size of motor required to drive the pump. It can also lead to potential startup failures during the service life of the pump.

[0004] It would be desirable to be able to reduce torque during start-up. Summary of the invention

[0005] A first aspect provides a rotary vane vacuum pump for evacuating a vacuum chamber, the rotary vane vacuum pump comprising: an inlet for connecting to the vacuum chamber and an outlet for discharging a fluid pumped by the vacuum pump; a stator and a rotor comprising a plurality of vanes, the rotor being configured to rotate within the stator, the rotor and the stator defining a plurality of pumping chambers for pumping fluid from the inlet to the outlet when the rotor rotates; a motor for driving the rotor; and a vent channel for providing fluid communication between the outside of the vacuum pump and the pumping chambers within the vacuum pump, the vent channel comprising a flow control device for controlling flow through the vent channel; the flow control device being configured to allow flow through the vent channel when the pump is started and to obstruct flow through the vent channel in response to at least one of the following: a predetermined time lapse, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from at least one sensor, the output from the at least one sensor indicating operation of the vacuum pump.

[0006] The inventors have recognized that the torque required to rotate the rotor of a vacuum pump (particularly a vacuum pump that is evacuated from atmospheric pressure) at startup can be very large and is often a limiting factor in the selection of a motor to drive the pump. They have also recognized that much of the required torque is due to the pressure differential across the blades during the initial rotation, and this can be alleviated by providing controlled ventilation of the pump at startup so that fluid can enter the inlet pumping chamber. After a certain point, flow through the vent channel can be blocked or stopped, and the vacuum pump can function in the usual manner. By reducing the pressure differential across the blades using a vent channel that provides a fluid path to an area that is not under reduced pressure, the maximum torque required during startup can be reduced. The vent channel can be vented to the atmosphere, or in some cases to an area of ​​increased pressure (such as an oil casing).

[0007] Selecting the point at which stopping ventilation is most preferred may be done based on one or more of several different factors dictating the operation of the pump. It may simply be some time after activation.

[0008] Alternatively, the decision to stop ventilation may be based on the operation of the pump itself, so it may be based on one or more of: the rotational speed of the rotor reaching a predetermined threshold, the motor current reaching a predetermined value, or an output from a sensor indicating some operating parameter of the vacuum pump. Basing the decision on the detected operation of the pump may allow ventilation to be stopped at a preferred or optimal point. The sensor may be a sensor associated with the vacuum pump, or it may be associated with the system that the pump is pumping.

[0009] In some embodiments, the vacuum pump comprises the at least one sensor. In some embodiments, the at least one sensor comprises at least one of a temperature sensor, a pressure sensor, a humidity sensor, and a sensor for sensing the number of rotations of the rotor.

[0010] Pressure, temperature, humidity and number of revolutions of the rotor since startup are all relevant to the current state of the vacuum pump, and one or more of these measurements may be used to decide to stop ventilating the pump.

[0011] In some embodiments, the inlet includes a movable closing element for opening or closing the inlet, and the movable closing element is configured to move between an open position and a closed position in response to the pressure on the vacuum pump side of the movable closing element rising above the pressure on the vacuum chamber side of the movable closing element; wherein the vent channel is fluidly connected to the vacuum chamber side of the movable element, so that the fluid control device allowing flow through the vent channel causes the movable element to move to the closed position.

[0012] The vacuum pump may have a movable closing element for sealing its inlet so that when the pump is closed, the vacuum chamber to which they are attached can be sealed in a vacuum state. In some cases, these movable closing elements are moved to a closed position under the control of a flow control device, which can be opened to allow flow through a channel, which changes the pressure on one side of the movable closing element so that the opening of the channel changes the pressure difference across the closing element, thereby pushing it to a closed position. The flow control device can conventionally be a solenoid valve controlled by the power sent to the motor so that when the motor is stopped, the valve opens and the closing element is closed, and when the motor is started, the valve is closed. In an embodiment, a system for controlling the movable closing element can be combined with a system for ventilating the pump at startup. In the case of this case, this can reduce the number of required flow control elements, wherein one flow control element (which can be a valve in some cases) is used to control the movable closing element and to ventilate the pump at startup. In this case, the closure of the valve is delayed instead of closing the valve immediately when the motor is started, so that during the initial stage of the rotation of the pump, there is ventilation to the pumping chamber and the movable closing element remains closed.

[0013] In some embodiments, the vent passage is configured to open into the rotary vane pump closer to the inlet of the vacuum pump than to the outlet.

[0014] The vent channel may open to the pump near the pump inlet, which is where gas pumping occurs. In some embodiments, it may open to the vacuum pump downstream of the inlet in the direction of rotation of the pump, so that the vent channel opens to the inlet pumping chamber.

[0015] In some embodiments, the vent channel provides venting to an exterior of the vacuum pump which is at atmospheric pressure.

[0016] In other embodiments, the vent passage provides venting to a pressure above atmospheric pressure.

[0017] In some embodiments, the rotary vane vacuum pump comprises a lubricant sealed sliding vane vacuum pump and the vent passage provides venting to a lubricant sleeve of the pump.

[0018] Where the vacuum pump is a lubricant sealed vacuum pump then venting the lubricant sleeve may be advantageous as this avoids lubricant contamination through the vent passage when the pump is stopped (such as during transport) which may be a problem.

[0019] The vent chamber provides venting by providing fluid communication between the interior of the pump and the exterior of the pump or the lubricant sleeve.The vent passage may open to the pumping chamber at one end and to somewhere outside the vacuum pump or into the lubricant sleeve of the vacuum pump at the other end.

[0020] In some embodiments, the flow control device is configured to open the vent channel or to close the vent channel.

[0021] In other embodiments, the flow control device is configured to control the degree of opening, and therefore flow, through the vent passageway.

[0022] While flow control may be accomplished in a number of ways, in some embodiments, the flow control device comprises a valve.

[0023] In some embodiments, the valve comprises a mechanical valve including a resilient member for biasing the closure element toward the closed position.

[0024] In other embodiments, the valve comprises an electrically controlled valve configured to operate in response to a control signal sent by control circuitry.

[0025] In the case where the valve is an electrically controlled valve, there may be control circuitry to control the valve. Such control circuitry may increase the complexity of the vacuum pump slightly, however, it may also allow a more careful control of the start-up phase and provide a very effective reduction in the maximum torque required.

[0026] In some embodiments, the rotary vane pump further includes a control circuit system configured to: control the motor for driving the pump; and control the flow control device; the control circuit system is configured to control the flow control device to allow flow through the ventilation channel when the pump is started, control the motor to start driving the pump, and then control the flow control device to block flow through the ventilation channel.

[0027] Although the control circuitry may simply control the valve to open after a predetermined time, in some cases it may be more sophisticated in its control and may be responsive to signals from one or more sensors in determining a preferred or optimal time to obstruct flow through the ventilation passageway. In some cases, the control circuitry may include an algorithm for determining when to stop ventilation based on multiple inputs.

[0028] A second aspect provides a method for starting a rotary vane vacuum pump according to the first aspect, the method comprising: controlling a flow control device to allow flow through a ventilation channel; starting rotation of a rotor of the pump; and obstructing flow through the ventilation channel in response to at least one of the following: a predetermined time lapse, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from a sensor, the output from the sensor indicating operation of the vacuum pump.

[0029] In some embodiments, the method further comprises causing a movable element to move from blocking an inlet of the vacuum pump to opening the inlet of the vacuum pump by said step of obstructing flow through the vent channel.

[0030] In some embodiments, the step of impeding flow through the vent channel comprises closing a valve.

[0031] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims where appropriate and in combinations other than those explicitly set out in the claims.

[0032] Where a device feature is described as being operable to provide a function, it will be appreciated that this includes device features that provide that function or that are adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the present invention will now be further described with reference to the accompanying drawings, in which:

[0034] Figure 1 A section through an oil-sealed vane pump and the required starting torque are shown;

[0035] Figure 2 Schematically illustrates a rotary vane pump according to an embodiment;

[0036] Figure 3 schematically illustrates a rotary vane pump according to a further embodiment;

[0037] FIG. 4A to FIG. 4C The different stages during startup are schematically shown;

[0038] Figure 5 shows the change in torque required for a pump according to the prior art and a pump according to an embodiment; and

[0039] Figure 6 Steps in a method according to an embodiment are shown. DETAILED DESCRIPTION

[0040] Before discussing the embodiments in more detail, an overview will first be provided.

[0041] When starting a vacuum pump, and particularly a sliding vane oil-sealed vacuum pump, there is a high load on the motor due to inertia, pressure differential across the vanes of the pump, and transport of oil. Embodiments seek to reduce the load experienced at start-up by venting the pump so that the pressure differential across the vanes of the pump is reduced by fluid flowing through a vent passage into the inlet of the pumping chamber. The venting can be accomplished by opening a valve in the flow path between the pumping chamber and the exterior of the stator.

[0042] The valve may be a mechanical valve that operates in response to a pressure differential, or it may be an electrically operated valve driven by electronic control circuitry.The valve may be a modulating valve or a binary valve having an ON / OFF state.

[0043] Control of the valve may be synchronised with the operation of the pump at start-up, for example with the pump rotation speed and / or time period.

[0044] For oil-sealed pumps, venting of the inlet pumping chamber limits the suction due to the pressure drop in the pump when the pump is stopped and during startup, and thus limits the amount of oil sucked into the pump from the oil casing. This reduces the amount of oil in the pump at startup, and the torque required at startup is correspondingly reduced. The conduit or channel for venting can lead to the outside, or it can be linked to the pump oil casing at increased pressure (atmospheric pressure + overpressure due to gas extraction).

[0045] The valve can be controlled by an on / off type switching valve or a proportional valve.

[0046] The motor power required at start-up is reduced by ventilation, and this allows the motor size to be reduced without reducing pump performance.

[0047] Some pumps are constructed with a solenoid valve that is used to control a movable closing element or baffle so that the pump is sealed and isolated from the vacuum chamber before stopping the pump. Such a valve controls the flow through the passage, which is used to increase the pressure on one side of the movable closing element so that the movable closing element moves to seal the pump and isolate it from the vacuum chamber. The valve can be a solenoid valve controlled by the pump power supply so that when the pump is powered on, the valve is closed. An embodiment connects the ventilation passage and the valve to an additional ventilation channel entering the pumping chamber so that the valve can be used to control the closure of the movable closing element and can also ventilate the pumping chamber to allow the pump to start more easily. In this case, the valve is closed at a certain point during the pump startup, rather than when the pump is powered on, and the certain point, for example, after a predetermined time or at a predetermined speed, the valve can be closed so that the pumping chamber is no longer ventilated, and the pressure in the pump is reduced and the movable closing element is opened.

[0048] In summary, integrated control and management of the solenoid valve allows the vent to remain open during the startup phase for one of the following and independently of the pump power supply: a defined time period; reaching a defined rotor speed or reaching a pressure, temperature, number of rotor revolutions or humidity.

[0049] Figure 1A sliding vane oil vacuum pump according to the prior art is shown, together with a graph showing the torque 50 required to drive the pump and the speed 40 of the pump as a function of time, the sliding vane oil vacuum pump comprising: a rotor 6 configured to rotate about an axis; sliding vanes 12 defining a pumping chamber; and a stator 5 within which the rotor 6 rotates. At startup, the pressure within the pump is at atmospheric pressure, and there is a large amount of gas transfer as the pump begins to rotate and due to the inertia of the rotor itself. This requires a large amount of initial torque to start the rotor rotation and reduce the pressure within the pump. Initially, the vanes 12 generate gas compression and suction, and also transport oil within the pump and the torque increases dramatically. Arrow 42 indicates a stage in which the vanes generate significant gas transfer, and the torque required to drive the motor is more than three times the torque required during steady-state operation. This initial high torque requirement can cause the pump to fail and requires a motor of larger size than when the pump is driven only during normal operating conditions, as can be seen from the torque graph.

[0050] Figure 2 A sliding vane pump according to an embodiment is schematically shown. The pump is connected to a vacuum chamber 2 and has a movable closing element or shutter 9 biased to a closed position by a spring 24. The pump 1 includes an exhaust port 4 and an inlet 3 linked to the vacuum chamber 2. There is also a vent channel 7 and a controllable valve 29. The valve allows ventilation of the inlet pumping chamber when it is open, so that if the valve is opened at startup, the pressure difference across the blades during the initial rotation of the rotor is reduced and the torque required for rotation is similarly reduced. Once the pump has rotated for a certain amount of time, or once a certain rotor speed or pressure or temperature has been reached, or once a certain number of rotor rotations have occurred, the valve 29 can be closed, whereupon the pump begins to reduce the pressure in the pumping chamber and the closing element 9 will open to connect the vacuum chamber to the pump and allow the pump to evacuate the vacuum chamber 2.

[0051] In this embodiment, there is an oil casing 32 supplying oil to the oil-sealed pump, and in this embodiment the vent channel 7 opens into this oil casing 32. This is at an increased pressure compared to atmospheric pressure. The advantage of venting into the oil casing is that contamination by oil in the exhaust gas leaking to the outside of the pump is avoided or at least hindered.

[0052] Figure 3A schematic diagram of a pump according to an embodiment is shown, wherein a vent channel 7 is adjacent to the pump inlet and when open serves to both vent the inlet pumping chamber and close the baffle 9. A vacuum pump 1 has an inlet 3 connected to a vacuum chamber 2 to be evacuated. The vacuum pump 1 has an outlet 4 for exhausting the pumped gas. The vacuum pump 1 has a stator 5 and a rotor 6 rotatably mounted within the stator 5, and includes an inlet or pumping area 8. There is a sensor 11 for measuring a parameter indicative of the operating state of the pump, and a control circuit system 15 that receives a signal from the sensor 11. There is also a motor 13 for driving the pump.

[0053] The control circuit system 15 controls the motor and the valve 7 for ventilating the pump, so that at startup the control circuit system controls the motor to start driving the rotor and the valve remains open. After a predetermined time, and / or upon receiving a signal from the sensor 11 indicating a predetermined condition (such as exceeding a threshold temperature), the control circuit system 15 controls the valve 7 to close, after which the shutter 9 will open and the pump 1 will start to evacuate the vacuum chamber 2.

[0054] FIG. 4A to FIG. 4C A startup procedure according to an embodiment is shown. Figure 4A The pump is shown stopped, the valve 29 is open, and the interior of the pump is at atmospheric pressure. The vacuum chamber 2 is at low pressure, and the inlet closure element 9 is closed. Figure 4B The pump is shown starting, with valve 29 still open to allow ventilation of air inside the pump as the rotor rotates, thereby reducing the pressure difference across the blades and the load on the motor. Figure 4C The situation is shown when the pump has reached a predetermined start condition, which may mean that a predetermined time has elapsed or some other operating threshold has been exceeded, and at this point valve 29 is closed and the pressure in the pump decreases until it exceeds the low pressure of the vacuum chamber 2, whereupon the closing element 9 opens and the pump operates to evacuate the vacuum chamber 2.

[0055] Figure 5 The speed achieved by the pump and the torque required to drive the pump are shown as a function of time at startup for a pump with and without a vent valve. The left Y-axis shows torque, the right Y-axis shows speed, and time is shown on the X-axis. Line 40 shows the rotor speed steadily increasing to operating speed, while line 50 shows the torque required for this initial acceleration and then the torque required to maintain this speed in a conventional pump without venting, and dashed line 60 shows the torque required for the pump initially vented according to an embodiment. As can be seen in both torque graphs, initially, there is a large amount of torque required, and once the rotor reaches a certain speed and the pressure in the pump and vacuum chamber has dropped, this amount of torque begins to drop.

[0056] In the case where there is a valve for venting the pump (dashed line 60), then the torque required at startup is less. It should be noted and as shown by this dashed line 60, although the torque required initially during startup is significantly reduced, it does remain higher for a longer time because if the pump is initially vented, it takes longer to evacuate the chamber and reach a stable low pressure state.

[0057] Figure 6 A flow chart illustrating steps in a method according to an embodiment is shown. In an initial step S10, the vent is controlled to open and the pump is stopped. At step S20, a start indication is received and in response, the motor starts driving the pump, the pump starts rotating and the vent remains open. At step D5, it is determined whether a predetermined start condition has been reached. The condition may be one or more of the following: a predetermined time has elapsed, a pressure, temperature or humidity threshold has been exceeded, or a number of rotations or rotation speed threshold has been exceeded.

[0058] When this condition has been met, the vent is closed at step S30. The pump then continues to pump and evacuate the pumping chamber. In the case where there is a baffle between the vacuum chamber and the vacuum pump, the baffle will open once the pressure in the pump has dropped to a value below the pressure in the vacuum chamber. At step S40, a stop command is received and pumping is stopped. At this point, the method returns to step S10, where the pump is stopped and the vent is opened. In some embodiments, in the case where the pump has a baffle to the pumping chamber, the baffle will be closed.

[0059] Although illustrative embodiments of the present invention have been disclosed in detail herein with reference to the accompanying drawings, it should be understood that the invention is not limited to the precise embodiments and that various changes and modifications can be effected therein by those skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0060] Reference numerals

[0061] 1 Vacuum pump

[0062] 2 Vacuum chamber

[0063] 3 Pump inlet

[0064] 4 Pump exhaust port

[0065] 5. Stator

[0066] 6 rotors

[0067] 7 ventilation channels

[0068] 8 Inlet or pumping area

[0069] 9 Closing element or flap

[0070] 11 Sensors

[0071] 12 sliding blades

[0072] 13 Motor

[0073] 15 Control circuit system

[0074] 24 Bias Devices

[0075] 29 Flow Control Device

[0076] 32 Oil casing

[0077] 40 Pump Speed

[0078] 50 standard pump torque

[0079] 60 Torque of the pump according to the embodiment

Claims

1. A rotary vane vacuum pump for evacuating gas from a vacuum chamber, the rotary vane vacuum pump comprising: an inlet for connection to the vacuum chamber and an outlet for exhausting the fluid pumped by the vacuum pump; a stator and a rotor including a plurality of blades, the rotor being configured for rotation within the stator, the rotor and stator defining a plurality of pumping chambers for pumping fluid from the inlet to the outlet as the rotor rotates; a motor for driving the rotor; as well as a vent passage for venting one of the plurality of pumping chambers within the vacuum pump, the vent passage including a flow control device for controlling flow through the vent passage; The flow control device is configured to allow flow through the ventilation passage when the pump is activated and to hinder flow through the ventilation passage in response to at least one of: a predetermined time lapse, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from at least one sensor, the output from the at least one sensor indicating operation of the vacuum pump.

2. The vacuum pump according to claim 1, wherein: The rotary vane vacuum pump further includes the at least one sensor including at least one of a temperature sensor, a pressure sensor, a humidity sensor, and a sensor for sensing a number of rotations of the rotor.

3. The rotary vane vacuum pump according to claim 1 or 2, wherein: The inlet includes a movable closing element for opening or closing the inlet, the movable closing element being configured to move between an open position and a closed position in response to a pressure on a vacuum pump side of the movable closing element rising above a pressure on a vacuum chamber side of the movable closing element; wherein, The vent channel is in fluid communication with the vacuum chamber side of the movable element such that the fluid control device permits flow through the vent channel to cause the movable element to move to the closed position.

4. A rotary vane vacuum pump according to any preceding claim, wherein: The vent passage is configured to open into the rotary vane pump closer to the inlet than to the outlet of the vacuum pump.

5. A rotary vane vacuum pump according to any preceding claim, wherein: The vent passage vents to a pressure above atmospheric pressure.

6. A rotary vane vacuum pump according to any preceding claim, wherein: The rotary vane vacuum pump comprises a lubricant sealed sliding vane vacuum pump, and the vent passage vents to a lubricant sleeve of the pump.

7. A rotary vane vacuum pump according to any preceding claim, wherein: The flow control device is configured to open the vent channel or to close the vent channel.

8. The rotary vane vacuum pump according to any one of claims 1 to 6, wherein: The flow control device is configured to control the degree of opening, and therefore flow, through the vent passageway.

9. A rotary vane vacuum pump according to any preceding claim, wherein: The flow control device comprises a valve.

10. The rotary vane vacuum pump according to claim 9, wherein: The valve comprises a mechanical valve including a resilient member for biasing the closure element toward the closed position.

11. The rotary vane vacuum pump according to claim 9, wherein: The valve comprises an electrically controlled valve configured to operate in response to a control signal sent by control circuitry.

12. A rotary vane vacuum pump according to any one of claims 1 to 9 or 11, further comprising a control circuit system, the control circuit system being configured to: controlling the motor for driving the vacuum pump; and controlling the flow control device; The control circuit system is configured to control the flow control device to allow flow through the ventilation channel when the pump is started, control the motor to start driving the pump, and then control the flow control device to block flow through the ventilation channel in response to at least one of the following: a predetermined time lapse, the rotational speed of the rotor reaching a predetermined threshold, the motor current reaching a predetermined value, and an output from the at least one sensor, wherein the output from the at least one sensor indicates the operation of the vacuum pump.

13. A method of starting a rotary vane vacuum pump according to any preceding claim, the method comprising: Controlling the flow control device to allow flow through the vent passage; initiating rotation of the rotor of the pump; as well as Flow through the vent passage is obstructed in response to at least one of: a predetermined time lapse, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from a sensor indicative of operation of the vacuum pump.

14. The method according to claim 13, further comprising: By the step of obstructing flow through the vent passage, a movable element is caused to move from blocking the inlet of the vacuum pump to opening the inlet of the vacuum pump.

15. The method according to claim 13 or 14, wherein: The step of impeding flow through the vent passage includes closing a valve.

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