Vacuum technology is widely spread in different technologies and made availa ble for numerous applications. Usually in those applications a vacuum system is connected to a vacuum chamber to be evacuated. Therein it is usually necessary that by the vacuum system the pressure in the vacuum chamber is below a given setpoint.

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 high est possible volumetric flow. Thus, on the one hand fast evacuation of the vac uum 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 be tween a maximum performance and a minimum performance.

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 vac uum system according to 1 as well as a vacuum system according to claim 11.

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 is a Variable Speed Drive pump (VSD). Therein, the first vacuum pump and the second vacuum pump are con nected 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 max imum pump rate of the first vacuum pump is 1.25 times to 4 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 preferably as described above comprises the steps of controlling the perfor mance 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 con nected to the vacuum chamber. Further, performance can be defined as ratio between the actual mass flow through the respective vacuum pump to the max imum mass flow through the respective vacuum pump. Alternatively, the per formance can be 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 can be defined as the ratio between the actual rotational speed of the respective vacuum pump to the maximum rotational speed of the respec tive 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 pres sure 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 second vacuum pump is a VSD wherein the performance of the second vacuum pump is controlled to be reduce while maintaining the set pressure. Thus, if the first vacuum pump is controlled to increase the perfor mance 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 perfor mance 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 or 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 vac uum 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 consump tion of the second vacuum pump can be greatly reduced reducing the overall energy consumption of the vacuum system.

In particular, if the pressure in the vacuum chamber is above the set pressure the first vacuum pump is operated at maximum performance and preferably 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 evac uation times of the vacuum chamber.

Alternatively, the maximum pump rate of the first vacuum pump is 1.25 times to 1.5 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 op eration 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 vac uum pump. Thus, a situation can be achieved in which the first vacuum pump is always running thereby reducing the power consumption of the second vac uum 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 pre determined 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 de scribed. In particular the first vacuum pump and preferably 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 de scribed together with the accompanied drawings.

The figures show:

Figure 1 a schematic drawing of the vacuum system according to the pre sent invention and

Figure 2 a flow diagram for the method according to the present invention.

The vacuum system according to the present invention comprises a vacuum chamber 12 to be evacuated and maintained at a set pressure. The vacuum chamber 12 is connected with an inlet 14 of the first vacuum pump 16. The outlet 18 of the first vacuum chamber 16 is connected to an inlet 20 of a second vacuum pump 22. Hence, the outlet pressure of the first vacuum pump 16 is equal to the inlet pressure of the second vacuum pump 22. The outlet 24 of the second vacuum pump 22 is connected to atmosphere or another backing pump. The first vacuum pump 16 can be built as one or more vacuum pumps connected in series or in parallel acting together. Also, the second vacuum pump 22 can be built by one or more vacuum pumps connected in series or parallel and acting together. The first vacuum pump 16 is connected to a control unit 26. Further, the second vacuum pump 22 is also connected to the control unit 26. In the present embodiment, the control unit 26 in connected to a pressure gauge 28 inside the vacuum chamber 12. By the control unit 26 the performance, i.e. volumetric flow, of the first vacuum pump 16 and/or second vacuum pump 22 can be controlled. Therein the first vacuum pump 16 is controlled to run always at the highest possible performance under which the pressure inside the vacuum chamber 12 is maintained. If the pressure inside the vacuum chamber 12 is below the set pressure, then the performance of the second vacuum pump is reduced. In particular, the first vacuum pump 16 is controlled to run always at a higher performance than the second vacuum pump 22. Thus, by the high performance of the first vacuum pump 16 the pressure at the inlet 20 of the second vacuum pump 22 is increased reducing the energy consumption of the second vacuum pump 22. Further, due to the increased inlet pressure of the second vacuum pump 22, rotational speed of the second vacuum pump 22 can be reduced without loss of vacuum in the vacuum chamber. Thus, the first vac uum pump 16 is controlled to maximize the inlet pressure of the second vacuum pump 22 by an increased performance, i.e. volumetric flow. Further, the second vacuum pump 22 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 16. Exceeding the allowable pressure difference between the inlet and outlet of the first vacuum pump 16 would overload the first vacuum pump 16. Therefore, it is preferred to implement a first vacuum pump 16 with a maximum pump rate greater than the maximum pump rate of the second vacuum pump. Figure 2 shows a flow diagram of the vacuum system of Figure 1.

In step SOI is system is turned on. Then, in step S02 it is checked whether the pressure PI inside the vacuum chamber 12 is larger or equal than the set pres sure Pset. If the pressure PI inside the vacuum chamber 12 is larger or equal than the set pressure Pset, then in step S03 the first vacuum pump 16 is con trolled 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 22 is controlled to operate in dependence on the pressure PI inside the vacuum chamber 12.

If the pressure inside the vacuum chamber 12 is below the set pressure, then in step S04 it is checked whether a stop level has been reached, i.e. PI is equal to or larger than Pset minus Stoplevel. If the pressure inside the vacuum cham ber 12 is below the stop level, then in step S06 the first vacuum pump 16 and the second vacuum pump 22 are both operated at their minimum performance.

If the pressure inside the vacuum chamber 12 is below the set pressure Pset but above the stop level, then in step S05 it is checked whether the second vacuum pump 22 is operated at minimum performance. If the second vacuum pump 22 is not operated at minimum performance, then it is returned to step S03 wherein the first vacuum pump 16 is controlled to operate at the maximum performance while the second vacuum pump 22 is controlled to operate in de pendence on the pressure PI inside the vacuum chamber 12. If the second vac uum pump 22 is operated at minimum performance, then in step S09 first vac uum pump 16 is controlled to operate in dependence on the pressure PI inside the vacuum chamber 12 while the second vacuum pump 22 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 16 or the second vacuum pump 22 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 12.

Hence, through the method according to the present invention the first vacuum pump is usually operated at a higher performance than the second vacuum pump. Due to this configuration the inlet pressure of the second vacuum pump is maximized. Thus, the required power consumption of the second vacuum pump is reduced, thereby reducing the overall power consumption of the vac uum system.