Patent Description:
The vacuum system usually comprises a vacuum pump. However, it is well known that the vacuum system comprises two vacuum pumps wherein a first vacuum pump is configured to achieve a low pressure or high vacuum. The first vacuum pump works together with a second vacuum pump or backing pump. The backing pump is configured to provide a high mass flow and being able to achieve a coarse vacuum. Upon evacuation of the vacuum chamber usually first the backing pump is evacuating the vacuum chamber up to a certain vacuum, i.e. down to a certain pressure. Then the first vacuum pump starts to generate the necessary low pressure equal to or below the given setpoint. Usually both vacuum pumps are operated constantly at maximum speed providing their highest possible volumetric flow. Thus, on the one hand fast evacuation of the vacuum chamber is guaranteed due to the provided pump performance while the pressure within the vacuum chamber can be maintained below the setpoint. However, due to this configuration a high power consumption of the vacuum system occurs.

Further, Variable Speed Drive pumps (VSD) are known that relate to vacuum pumps with adjustable rotational speed in order to control the performance of the vacuum pump. Therein the performance of the VSD can be controlled between a maximum performance and a minimum performance.

<CIT>, <CIT> and <CIT> are relevant prior art documents. In view of the present invention, specific reference is made to <CIT> which discloses a method for lowering the pressure in a vacuum chamber, which involves controlling the speed of the high vacuum pump of a vacuum system in which two pumps are connected in series. During lowering the pressure, the speed of the high vacuum pump is controlled in function of an operating parameter of said pump.

It is an object of the present invention to provide a vacuum system and a method for operating such a vacuum system that can be operated in an energy efficient manner to maintain a vacuum in a vacuum chamber.

The solution of the present problem is provided by a method to operate a vacuum system according to <NUM> as well as a vacuum system according to claim <NUM>.

According to the present invention the vacuum system comprises at least a first vacuum pump and a second vacuum pump wherein the first vacuum pump and the second vacuum pump are connectable to the vacuum chamber to maintain a set pressure. Therein the first vacuum pump and the second vacuum pump are Variable Speed Drive pumps (VSD). Therein, the first vacuum pump and the second vacuum pump are connected in series. Therein an inlet of the first vacuum pump is connectable to the vacuum chamber wherein the outlet of the first vacuum pump is connected to the inlet of the second vacuum pump. The outlet of the second vacuum pump might be connected to the atmosphere or to a further backing pump. The maximum pump rate of the first vacuum pump is <NUM> times to <NUM> times larger than the maximum pump rate of the second vacuum pump.

The method in accordance to the present invention to operate a vacuum system as described above comprises the steps of controlling the performance of the first vacuum pump wherein the performance of the first vacuum pump is controlled to be equal to or higher than the performance of the second vacuum pump while maintaining the set pressure in the vacuum chamber. Therein the first vacuum pump is defined as the vacuum pump directly connected to the vacuum chamber. As a first option, performance is defined as ratio between the actual mass flow through the respective vacuum pump to the maximum mass flow through the respective vacuum pump. Alternatively, the performance is defined as the volumetric flow of the vacuum pump or the relative volumetric flow, i.e. the ratio between the actual volumetric flow and the maximum volumetric flow of the respective vacuum pump. Alternatively, the performance is defined as the ratio between the actual rotational speed of the respective vacuum pump to the maximum rotational speed of the respective vacuum pump.

It has been noted that the power consumption of a vacuum pump is related to the rotational speed and inlet pressure. Thus, power consumption of a vacuum pump can be decreased, for a set inlet pressure, by reducing the rotational speed of the vacuum pump. Further, it has been noted by the present invention that the backing pump, i.e. the second vacuum pump, is usually the largest energy consumer in such a vacuum system. This is since the second vacuum pump is usually configured to be able to fast evacuate the vacuum chamber resulting in a high mass flow though the second vacuum pump. However, by the present invention the first vacuum pump is controlled to operate at a higher performance than the second vacuum pump while the pressure in the vacuum chamber is maintained equal to or below the set pressure due to the combined action of the first vacuum pump and second vacuum pump. Thus, the inlet pressure of the second vacuum pump is increased while decreasing the rotational speed of the second vacuum pump resulting in a reduced power consumption of the second vacuum pump. In accordance to the present invention under the presumption of maintaining the set pressure, the inlet pressure of the second vacuum pump is maximized while the rotational speed of the second vacuum pump is minimized to achieve the effect of the present invention to minimize power consumption without overloading either one of the vacuum pumps.

In particular, the first vacuum pump is a roots pump, a molecular drag pump or a turbomolecular pump.

In particular, the second vacuum pump is a screw pump, scroll pump, rotary vane pump, claw pump or the like.

In particular, the performance of the second vacuum pump is controlled to be reduced while maintaining the set pressure. Thus, if the first vacuum pump is controlled to increase the performance usually this will result in a reduction of pressure inside the pressure chamber. However, to further reduce the energy consumption of the vacuum system the second vacuum pump can be controlled to reduce its performance while maintaining the set pressure and compensating for the increase of performance of the first vacuum pump.

In particular, the first vacuum pump and/or the second vacuum pump comprises more than one vacuum pump preferably connected in parallel. Thus, the first vacuum pump and/or the second vacuum pump is built as one or more vacuum pumps acting together. Each vacuum pump connected in parallel comprise a common inlet and a common outlet. Therein, at least one of the vacuum pumps of the first vacuum pump and at least one of the vacuum pumps of the second vacuum pump is built as a VSD. Thus, for example if the first vacuum pump comprises two vacuum pumps then one of these two vacuum pumps can be operated always at maximum performance while the other vacuum pump of the first vacuum pump can be operated in accordance to the above described method. The same applies also to the second vacuum pump. Of course, it is possible to control all vacuum pumps of the first vacuum pump and/or all vacuum pumps of the second vacuum pump in the same manner.

In particular, the performance of the first vacuum pump is maximized and the performance of the second vacuum pump is minimized while maintaining the set pressure. If the vacuum chamber is evacuated and the vacuum system is in the operational state of maintaining the set pressure of the vacuum chamber, the first vacuum pump is operated at maximum performance while the second vacuum pump is operated at minimum performance. Thus, the power consumption of the second vacuum pump can be greatly reduced reducing the overall energy consumption of the vacuum system.

According to the present invention, if the pressure in the vacuum chamber is above the set pressure the first vacuum pump is operated at maximum performance and the second vacuum pump is operated in dependence on the pressure. Thus, the second vacuum pump is operated to meet the requirements of the application in order to achieve sufficiently fast the desired vacuum below the set pressure in the vacuum chamber.

In particular, if the pressure in the vacuum chamber is equal to or below the set pressure, the second vacuum pump is operated at minimum performance. Thus, the energy consumption of the vacuum system can be minimized. Preferably, the vacuum pump is then operated in dependence on the pressure inside the vacuum chamber. Thus, if the pressure in the vacuum chamber is equal to or below the set pressure the first vacuum pump is operated in dependence on the pressure in the vacuum chamber to meet the applications requirements and maintain the desired pressure in the vacuum chamber.

In particular, the maximum pump rate of the first vacuum pump is two times to four times larger than the maximum pump rate of the second vacuum pump. Thus, the maximum pump rate of the first vacuum pump is larger than the maximum pump rate of the second vacuum pump providing sufficient fast evacuation times of the vacuum chamber.

Alternatively, the maximum pump rate of the first vacuum pump is <NUM> times to <NUM> times larger than the maximum pump rate of the second vacuum pump. Thus, by the first vacuum pump having a maximum pump rate comparable to or slightly above the maximum pump rate of the second vacuum pump, an operation state can be easily maintained in which the performance of the first vacuum pump is selected to be higher than the performance of the second vacuum pump. Thus, a situation can be achieved in which the first vacuum pump is always running thereby reducing the power consumption of the second vacuum pump and also reducing the power consumption of the overall vacuum system.

In particular, the performance of the first vacuum pump and/or second vacuum pump is increased at least above a threshold if the first vacuum pump and/or the second vacuum pump is running at a speed below the threshold for a predetermined time. If the first vacuum pump or second vacuum pump is running at a speed below the threshold the lubrication of the bearings of the first vacuum pump or second vacuum pump might become insufficient. Thus, increased wear or damaged to the bearings of the first vacuum pump or second vacuum pump might occur. In order to avoid this situation, the speed, i.e. performance, of the first vacuum pump or the second vacuum pump, respectively, is increased above the threshold in order to ensure sufficient lubrication of the bearings of the respective vacuum pump.

Further, the present invention relates to a vacuum system as previously described. In particular the first vacuum pump and also the second vacuum pump are connected to a control unit wherein the control unit is adapted to carry out the method as described above.

In the following the present embodiments of the present invention will be described together with the accompanied drawings.

The vacuum system according to the present invention comprises a vacuum chamber <NUM> to be evacuated and maintained at a set pressure. The vacuum chamber <NUM> is connected with an inlet <NUM> of the first vacuum pump <NUM>. The outlet <NUM> of the first vacuum chamber <NUM> is connected to an inlet <NUM> of a second vacuum pump <NUM>. Hence, the outlet pressure of the first vacuum pump <NUM> is equal to the inlet pressure of the second vacuum pump <NUM>. The outlet <NUM> of the second vacuum pump <NUM> is connected to atmosphere or another backing pump.

The first vacuum pump <NUM> can be built as one or more vacuum pumps connected in series or in parallel acting together. Also, the second vacuum pump <NUM> can be built by one or more vacuum pumps connected in series or parallel and acting together. The first vacuum pump <NUM> is connected to a control unit <NUM>. Further, the second vacuum pump <NUM> is also connected to the control unit <NUM>. In the present embodiment, the control unit <NUM> in connected to a pressure gauge <NUM> inside the vacuum chamber <NUM>. By the control unit <NUM> the performance, i.e. volumetric flow, of the first vacuum pump <NUM> and/or second vacuum pump <NUM> can be controlled. Therein the first vacuum pump <NUM> is controlled to run always at the highest possible performance under which the pressure inside the vacuum chamber <NUM> is maintained. If the pressure inside the vacuum chamber <NUM> is below the set pressure, then the performance of the second vacuum pump is reduced. In particular, the first vacuum pump <NUM> is controlled to run always at a higher performance than the second vacuum pump <NUM>. Thus, by the high performance of the first vacuum pump <NUM> the pressure at the inlet <NUM> of the second vacuum pump <NUM> is increased reducing the energy consumption of the second vacuum pump <NUM>. Further, due to the increased inlet pressure of the second vacuum pump <NUM>, rotational speed of the second vacuum pump <NUM> can be reduced without loss of vacuum in the vacuum chamber. Thus, the first vacuum pump <NUM> is controlled to maximize the inlet pressure of the second vacuum pump <NUM> by an increased performance, i.e. volumetric flow. Further, the second vacuum pump <NUM> is controlled to be operated at minimum rotational speed to achieve a minimized energy consumption while maintaining the set pressure in the vacuum chamber. However, the maximum inlet pressure is limited by the first vacuum pump <NUM>. Exceeding the allowable pressure difference between the inlet and outlet of the first vacuum pump <NUM> would overload the first vacuum pump <NUM>. Therefore, a first vacuum pump <NUM> with a maximum pump rate greater than the maximum pump rate of the second vacuum pump is implemented.

<FIG> shows a flow diagram of the vacuum system of <FIG>.

In step S01 is system is turned on. Then, in step S02 it is checked whether the pressure P1 inside the vacuum chamber <NUM> is larger or equal than the set pressure Pset. If the pressure P1 inside the vacuum chamber <NUM> is larger or equal than the set pressure Pset, then in step S03 the first vacuum pump <NUM> is controlled to operate at the maximum performance. This maximum is depending on inlet and outlet pressure, thus also depending on the speed of the second pump. The second vacuum pump <NUM> is controlled to operate in dependence on the pressure P1 inside the vacuum chamber <NUM>.

If the pressure inside the vacuum chamber <NUM> is below the set pressure, then in step S04 it is checked whether a stop level has been reached, i.e. P1 is equal to or larger than Pset minus Stoplevel. If the pressure inside the vacuum chamber <NUM> is below the stop level, then in step S06 the first vacuum pump <NUM> and the second vacuum pump <NUM> are both operated at their minimum performance.

If the pressure inside the vacuum chamber <NUM> is below the set pressure Pset but above the stop level, then in step S05 it is checked whether the second vacuum pump <NUM> is operated at minimum performance. If the second vacuum pump <NUM> is not operated at minimum performance, then it is returned to step S03 wherein the first vacuum pump <NUM> is controlled to operate at the maximum performance while the second vacuum pump <NUM> is controlled to operate in dependence on the pressure P1 inside the vacuum chamber <NUM>. If the second vacuum pump <NUM> is operated at minimum performance, then in step S09 first vacuum pump <NUM> is controlled to operate in dependence on the pressure P1 inside the vacuum chamber <NUM> while the second vacuum pump <NUM> is controlled to operate at the minimum performance.

If both vacuum pumps are operated at their minimum performance, then in step S07 it is checked whether the first vacuum pump <NUM> or the second vacuum pump <NUM> is operated at minimum performance for a predetermined time. If the predetermined time has been reached, then in step S08 the vacuum system is tuned off.

The above described method is repeatedly applied in dependence on a change of the pressure inside the vacuum chamber <NUM>.

Claim 1:
Method to operate a vacuum system comprising at least a first vacuum pump (<NUM>) and a second vacuum pump (<NUM>), wherein the first vacuum pump and the second vacuum pump are connectable to a vacuum chamber (<NUM>) to maintain a set pressure (Pset), wherein the first vacuum pump and second vacuum pump are variable speed drive pumps (VSD), wherein the first vacuum pump and the second vacuum pump are connected in series such that the outlet (<NUM>) of the first vacuum pump is connected to the inlet (<NUM>) of the second vacuum pump, and wherein the maximum pump rate of the first vacuum pump is <NUM> times to <NUM> times larger than the maximum pump rate of the second vacuum pump, the method comprises the steps of:
controlling the performance of the first vacuum pump, wherein the performance of the first vacuum pump is controlled to be equal to or higher than the performance of the second vacuum pump while maintaining the set pressure in the vacuum chamber, and
operating the first vacuum pump at maximum performance and operating the second vacuum pump in dependence on the pressure, if the pressure (P1) in the vacuum chamber is above the set pressure,
wherein the performance of a vacuum pump is defined as one of:
the ratio between the actual mass flow through the respective vacuum pump to the maximum mass flow through the respective vacuum pump;
the ratio between the actual volumetric flow and the maximum volumetric flow of the respective vacuum pump; or
the ratio between the actual rotational speed of the respective vacuum pump to the maximum rotational speed of the respective vacuum pump.