Maintenance method for monitoring and maintaining an electric compressor

Abstract

The invention relates to a maintenance method (25) for monitoring and maintaining electric compressors (7), in particular for circulating a laser gas (4) in a CO2 laser system (1), comprising the method steps of: b) reducing (26) a compressor speed (27) of the electric compressor (7) by changing a drive mode of an electric drive unit (22) of the electric compressor (7) into a generator mode; c) determining (32) a speed reduction by detecting the compressor speed (27) as a function of time (30); d) comparing (36) the speed reduction, in particular a deceleration curve (31), with at least one stored reference speed reduction (33); e) outputting (37) a maintenance recommendation on the basis of the comparison from method step d).

Description

[0001] Wartuna method for monitoring and maintaining an electric compressor

[0002] The invention relates to a maintenance method for monitoring and maintaining electric compressors.

[0003] Such electric compressors are used particularly in CO2 laser systems to circulate a laser gas required for generating a laser beam within a closed laser gas circuit.

[0004] A CO2 laser system can be understood to consist of a CO2 laser beam source and / or a CO2 laser beam amplifier. In the latter case, the CO2 laser beam amplifier typically serves to amplify a seed laser beam emitted by a seed laser, in particular a CO2 laser beam source.

[0005] A CO2 laser beam source typically comprises at least one discharge tube in which a laser gas serves as the laser medium. Furthermore, the CO2 laser beam source typically includes at least one electric compressor for supplying the laser gas to the at least one discharge tube via at least one supply element, and for removing the laser gas from the at least one discharge tube via at least one discharge element within the closed laser gas circuit.

[0006] The laser gas in a CO2 laser system is typically a mixture of helium, nitrogen, and CO2. CO2 serves as the actual laser medium, while the helium and nitrogen molecules play a supporting role. A CO2 laser beam source is excited electrically. Within the discharge tube, typically a quartz glass tube, the laser gas is excited by a gas discharge at high DC voltage or high-frequency AC voltage. This excitation results in a population inversion. In the case of a CO2 beam source in the form of a CO2 laser, the laser medium is located in the beam path of a mirror array acting as a laser resonator.

[0007] Since the laser gas heats up considerably during operation of the CO2 laser beam source, and the laser process ceases at temperatures above 300°C, the laser gas must be cooled. Such cooling is achieved by removing the laser gas from the discharge tubes and re-feeding it into the discharge tubes in a closed laser gas circuit, using suitable additional equipment such as heat exchangers.

[0008] CO2 laser systems, in the form of CO2 laser beam amplifiers, are used primarily for generating extreme ultraviolet (EUV) radiation. EUV radiation refers to electromagnetic radiation with a wavelength between 8 nm and 15 nm. Compared to the currently widespread use of wavelengths around 200 nm, the use of EUV radiation for microlithographic manufacturing in the semiconductor industry allows for the reliable production of components with significantly smaller feature sizes, thus leading to a corresponding increase in performance. In the so-called "Laser Produced Plasma" (LPP) process, tin droplets are bombarded with laser pulses, which have been amplified in a CO2 laser beam amplifier, to generate the EUV radiation. The bombardment of the tin droplets creates a plasma that emits the EUV radiation.

[0009] Electric compressors, particularly in the aforementioned CO2 laser systems, represent a functionally critical component without which the CO2 laser system cannot operate. The electric drive unit of the compressor, typically an electric motor, is subjected to high mechanical and thermal stresses, necessitating regular replacement. If an electric compressor fails, this can lead to significant downtime, maintenance effort, and maintenance costs. Furthermore, the resulting downtime causes considerable production delays, incurring additional expenses.

[0010] From DE 10 2017 204 645 A1, a method and a device for detecting the operating state of an electric motor are known. The method involves comparing a measured induced voltage and / or a measured induced current of the electric motor with predefined reference values ​​in order to infer the operating state. However, the described method is technically complex to implement, so that the requirements for simple monitoring and maintenance of the electric compressor cannot be met.

[0011] The object of the invention is to provide a technically simple, cost-effective, fast and precise monitoring of the condition of an electric compressor.

[0012] This problem is solved according to the invention by a maintenance method having the features of claim 1. The dependent claims describe preferred embodiments of the invention.

[0013] According to the invention, a maintenance procedure is provided.

[0014] The maintenance procedure is designed and configured for monitoring and maintaining electric compressors. In particular, the maintenance procedure is designed and configured for monitoring and maintaining electric compressors designed to circulate a laser gas in a CO2 laser system.

[0015] The maintenance procedure comprises at least the following steps: In step b) of the maintenance procedure, the compressor speed is reduced by changing the drive mode of the electric compressor's drive unit to a generator mode. A drive mode is defined as operating the electric drive unit at a predetermined drive power or speed. The drive power of the electric drive unit is typically reduced or completely stopped. The inertia of the electric drive unit, and in particular the inertia of the electric compressor, maintains the rotational movement, which, however, decreases continuously. As a result of the maintained rotational movement, a voltage is induced in the electric drive unit, causing it to operate as a generator.

[0016] Step c) of the maintenance procedure involves determining a decrease in the speed of the electric drive unit, in particular the electric compressor. This decrease is determined by measuring the compressor speed of the electric drive unit, or the electric compressor, over time.

[0017] The compressor speed can be determined by measuring the induced voltage in the electric drive unit or a change in the magnetic field. Typically, the induced voltage in the electric drive unit depends on the speed of the electric drive unit or the compressor speed. This eliminates the need for additional sensors. Preferably, the induced voltage is measured by an upstream frequency converter and assigned to a specific speed of the electric compressor. Alternatively or additionally, the compressor speed can be determined by directly measuring the speed using suitable sensors. For example, the compressor speed can be measured using a Hall effect sensor.

[0018] By recording the compressor speed over time, the speed reduction of the electric compressor can be presented as a delay curve. A delay curve allows for a particularly fast and technically simple evaluation of the speed reduction.

[0019] A further step d) of the maintenance procedure involves comparing the speed reduction with at least one stored reference speed reduction. In other words, the recorded speed reduction, in particular the deceleration curve, is evaluated.

[0020] A reference speed reduction can be understood as a representative value and / or a representative curve that describes the deceleration of the electric compressor in proper working order. In other words, the reference speed reductions were generated in the proper working order of the electric compressor and / or other, particularly identical, electric compressors. This allows for a more accurate comparison of the speed reduction with the reference speed reductions.

[0021] The comparison typically involves detecting deviations between the speed reduction and the stored reference speed reductions. Specifically, it can be determined whether the speed reduction occurs faster than the reference speed reduction. For this purpose, a stored speed gradient of the reference speed reduction can be compared with a maximum speed gradient of the detected speed reduction. If the delay of the detected speed reduction deviates too significantly from the reference speed reduction, a deterioration of the electric compressor's condition can be inferred. A deviation between the speed reduction and the stored reference speed reductions could, for example, be such that a malfunctioning electric compressor exhibits a higher absolute speed reduction than the stored reference speed reductions.In other words, a malfunctioning electric compressor in generator mode can decelerate faster than would be expected from a fully functional electric compressor.

[0022] In step d) of the maintenance procedure, a maintenance recommendation is generated based on the comparison. This recommendation is preferably displayed visually, for example, on a screen. The recommendation typically includes information about the detected speed reduction, at least a reference speed reduction, and / or the result of the comparison. This allows necessary maintenance and / or repairs to be identified and carried out early on.

[0023] In summary, the invention proposes a maintenance method in which the electric compressor is monitored by detecting and comparing changes in its rotational speed. The inventors have recognized that electric compressors, or the electric drive units of electric compressors, requiring maintenance exhibit an increased incidence of short circuits, which lead to higher electromagnetic losses. This results in a greater deceleration of the electric drive unit, or a shortened rundown time of the electric compressor. Knowing the duration and / or degree of deceleration allows conclusions to be drawn about electromagnetic losses in the electric drive unit of the electric compressor and thus indicates the need for maintenance or replacement.An unplanned failure of the electric compressor can therefore be effectively avoided with technically simple means or even predicted within the framework of what is sometimes called "predictive maintenance".

[0024] Preferably, the maintenance procedure is repeated several times, particularly regularly, for an electric compressor, with the recorded speed reduction being stored as a reference speed reduction. This allows for the continuous monitoring of changes in the condition of the electric compressor and its use in assessing the need for maintenance. Maintenance can thus be predicted with particular reliability.

[0025] A preferred embodiment of the maintenance procedure includes the additional process step a), in which the pressure downstream of the compressor impeller is reduced. In other words, the overpressure generated on the downstream side of the electric compressor is discharged by means of suitable technical devices. This allows the downstream pressure of the electric compressor to be adjusted to the upstream pressure, thus preventing excessive deceleration of the electric compressor. The maintenance procedure can therefore be carried out without or with only a low downstream pressure and without power input, allowing the electric compressor, and in particular the impeller, to coast to a complete stop. In other words, the electric compressor coasts to a stop. This allows the maintenance procedure to be carried out more precisely and repeatably.Procedure step a) is typically carried out before procedure step b).

[0026] To reduce the downstream pressure, a pump, in particular a vacuum pump, and / or at least one openable drain valve can be used. The drain valve can, for example, open a bypass between the upstream and downstream sides of the electric compressor. A preferred embodiment of the maintenance procedure involves reducing the pressure to a value significantly below ambient pressure. Preferably, the pressure is reduced to a value of <100 hPa, more preferably to a value of <50 hPa, and most preferably to a value of 10 hPa. This minimizes the influence of the downstream pressure and allows the maintenance procedure to be carried out with particular precision.

[0027] In a preferred embodiment of the maintenance method, the at least one reference speed reduction is stored as at least one speed gradient and / or as at least one speed characteristic curve. The reference speed reduction is preferably generated in a properly functioning electric compressor.

[0028] Following a preferred further development of the maintenance procedure, a number of speed characteristic curves are stored. Typically, a large number of reference speed reductions are stored. This allows measurement and manufacturing tolerances to be taken into account.

[0029] Maintenance method according to one of the preceding claims, wherein the reference speed reduction is stored as a reference measurement of the same electric compressor. This allows deviations to be detected particularly quickly and even more reliably.

[0030] According to a preferred embodiment of the maintenance procedure, the compressor speed is reduced over a predetermined delay period. In other words, the delay period of the electric compressor is defined, and the speed reduction within this delay period is recorded. This allows the maintenance procedure to be particularly well adapted to available production downtimes.

[0031] A preferred further development of the maintenance procedure provides that the delay period is at least 50 seconds, preferably at least 100 seconds, and particularly preferably at least 150, 200, or 250 seconds. With increasing delay periods, deviations can be determined more accurately.

[0032] In a preferred embodiment of the maintenance procedure, the compressor speed is reduced to a predetermined minimum speed. In other words, alternatively or in addition to a predetermined delay period, a speed can be predefined that is to be reached during the maintenance procedure. This reliably prevents insufficient speed reduction during the maintenance procedure, which would lead to an unreliable determination of deviations.

[0033] A further development of the maintenance procedure stipulates that the minimum speed is predetermined as a standby speed for the compressor. A standby speed can be understood as a low-consumption operating speed of the electric compressor, which enables a rapid return to operating speed. This allows for a particularly quick resumption of operation. Alternatively, the minimum speed can be predetermined as a standstill of the compressor. When the compressor stands still, the speed is reduced until it stops. With the minimum speeds described above, the maintenance procedure can be particularly well integrated into existing operating processes of the electric compressor. Furthermore, it ensures that the maintenance procedure is carried out at regular intervals, thus guaranteeing the predictability of maintenance needs.

[0034] A particularly preferred embodiment of the maintenance procedure is one in which process step d) is performed automatically by maintenance software. In other words, the comparison between the detected speed reduction and the reference speed reduction is carried out automatically, i.e., without any operator intervention. This allows the maintenance procedure to be integrated into the operational process in a particularly automated manner.

[0035] In a preferred embodiment of the maintenance procedure, the maintenance recommendation includes the comparison from procedure step d) and / or a determined current state of the electric compressor, in particular the electric drive unit. This enables particularly rapid identification of maintenance tasks.

[0036] In a preferred embodiment of the maintenance procedure, the maintenance recommendation includes an indication of the urgency of maintenance for the electric compressor, in particular the electric drive unit. This allows for the prioritization of maintenance tasks.

[0037] Further advantages of the invention will become apparent from the claims, the description, and the drawing. Likewise, the features mentioned above and those described in more detail below can each be used individually or in any suitable combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention.

[0038] Detailed description of the invention and drawing

[0039] Fig. 1 shows a top view of a CO2 laser system in the form of a CO2 laser beam sluice with a folded laser resonator in a sectional view.

[0040] Fig. 2 shows a perspective view of the CO2 laser system shown in Fig. 1 in the form of a CO2 laser beam sluice with a centrally arranged electric compressor. Fig. 3 schematically shows a maintenance procedure for monitoring and maintaining an electric compressor.

[0041] Fig. 4 schematically shows a reduction in speed detected by reducing the compressor speed of the electric compressor.

[0042] Figures 1 and 2 show a CO₂ laser system 1 in the form of a CO₂ laser beam source. As shown, the CO₂ laser system 1 can have a square-folded laser resonator 2 and be essentially rotationally symmetrical in fourfold fashion.

[0043] According to the illustrated embodiment, a laser gas 4, consisting of CO2, He, and N2 and serving as the laser medium, can be excited via electrodes 5 in discharge tubes 3. The electrodes 5 are arranged adjacent to the discharge tubes 3 and connected to an RF generator (not shown). For example, a vacuum tube generator with an excitation frequency of 13.56 MHz or 27.12 MHz can be used as the RF generator. The excitation of the laser gas 4 leads to a population inversion, and a laser beam 6 is formed in the laser resonator 2.

[0044] To cool the laser gas 4, it is drawn off or extracted from the discharge tubes 3 by means of an electric compressor 7, here a radial compressor, centrally arranged in the folded laser resonator 2, and, after cooling, returned to the discharge tubes 3 in a closed laser gas circuit K. In other words, the electric compressor 7 causes the laser gas 4 to circulate. For this purpose, the CO₂ laser system 1 has, for example, four feed arms 8 as first feed elements and four second feed elements 9, 9', as well as four first discharge elements 10 and four discharge arms 11 as second discharge elements.

[0045] The four feed arms 8 and the four discharge arms 11 are arranged radially in a first plane 12 of the CO2 laser system 1, as shown in the illustration, while the discharge tubes 3 are arranged in a second plane 13 and are alternately connected to each other via the second feed elements 9, 9' and the first discharge elements 10. The second feed elements 9, 9' form the corners of the square laser resonator 2, while the first discharge elements 10 are arranged centrally along the edges of the square laser resonator 2.

[0046] The flow direction of the laser gas 4 inside the discharge tubes 3, as well as in the feed elements 8, 9, 9' and the discharge elements 10, 11, is illustrated by arrows in Fig. 1. Starting from the electric compressor 7, the laser gas 4 flows through the four feed arms 8 and the four second feed elements 9, 9' arranged in the corners of the square laser resonator 2 into the discharge tubes 3. The laser gas 4 then flows through the discharge tubes 3 and via the first discharge elements 10 and the discharge arms 11 back to the electric compressor 7.

[0047] The laser beam 6 travels along the axes of the discharge tubes 3. Deflection mirrors 14 in the second feed elements 9 deflect the laser beam 6 by 90° each. In one of the second feed elements 9', a first resonator mirror 15 and a partially transmissive second resonator mirror 16 are arranged. The first resonator mirror 15 is highly reflective and reflects the laser beam 6 by 180°, so that the laser beam 6 passes through the discharge tubes 3 again in the opposite direction. The partially transmissive second resonator mirror 16 serves as an output coupler, via which a portion 6' of the laser beam 6 is coupled out of the laser resonator 2, while the other portion remains in the laser resonator 2 and passes through the discharge tubes 3 again.

[0048] Alternatively, unlike the representation shown here, the CO2 laser system 1 can also have two sublevels of discharge tubes 3 to increase power. These sublevels are connected to each other via the second feed elements 9, 9' and the first discharge elements 10. The laser beam 6 is then redirected between the sublevels, for example, via periscopes. As an alternative to the representation in Fig. 1 and Fig. 2, the CO2 laser system 1 can also be a CO2 laser beam amplifier. In this case, the resonator mirrors 15, 16 can be replaced by transmissive elements, in particular windows. A laser beam 6 to be amplified, for example in the form of a seed laser beam, then passes through the CO2 beam source only once.

[0049] Figure 2 shows a partial section of a feed arm 8 and a discharge arm 11. As shown, a section 17 inside each feed arm 8 and discharge arm 11 can be designed as a heat exchanger. To fulfill the function as a heat exchanger, in the CO2 laser beam source shown as an example in Figure 2, egg-shaped cooling tubes are guided through these sections 17, through which a cooling fluid flows.

[0050] Upstream of the subsections 17, a catalyst 18 for catalyzing the oxidation of dissociation products 19 (see Fig. 1), which are formed when the laser gas 4 is excited, in particular CO, can be arranged in a feed arm 8 and a discharge arm 11. An advantage of this arrangement is the comparatively high catalyst temperatures while maintaining sufficient distance from the discharge tubes 3. The temperature TI in the region of the catalyst 18 in the discharge arm 11 is typically in the range of 150°C to 250°C, while the temperature T2 in the region of the catalyst 18 in the feed arm 8 is typically in the range of 60°C to 100°C.

[0051] As can also be seen in Fig. 2, the feed arms 8 and discharge arms 11 each have a closable opening 21 for replacing the catalysts 18. The openings 21 can be closed, for example, by means of plates or flaps, which may be removable or pivotable. The catalysts 18 are designed as separate components in the form of cassettes, which greatly simplifies their replacement. The electric compressor 7 typically comprises, as shown, an electric drive unit 22, for example, an electric motor, a compressor impeller 23, and a frequency converter 24. The frequency converter 24 can be designed, for example, as an SOTL frequency converter or an MC53 frequency converter.

[0052] The frequency converter 24 is designed to provide controllable drive power to the electric drive unit 22. In other words, the rotational speed or rotational speed of the electric compressor 7 can be adjusted as required to the required circulation speed of the laser gas 4 in the laser gas circuit K.

[0053] Fig. 3 schematically shows a maintenance method according to the invention 25.

[0054] Maintenance method 25 is suitable and designed for monitoring and maintaining electric compressors 7 (see Figs. 1, 2). In particular, maintenance method 25 is designed and configured for monitoring and maintaining electric compressors 7 that are configured for circulating the laser gas 4 (see Figs. 1, 2) in a CO2 laser system 1 (see Figs. 1, 2).

[0055] The maintenance procedure 25 is explained below with exemplary reference to the other figures 1, 2, 4 and the CO2 laser system 1 shown therein.

[0056] Maintenance procedure 25 includes at least the following procedural steps:

[0057] In process step 26 of the maintenance process 25, a reduction of the compressor speed 27 (see Fig. 4) of the electric compressor 7 is provided. In other words, the rotational speed of the compressor impeller 23 (see Fig. 2) is slowed down. According to the invention, the reduction of the compressor speed 27 is effected by at least temporarily changing the drive mode of the electric drive unit 22 (see Fig. 2), or the electric motor, into a generator mode. This can be achieved by reducing, preferably by disabling, the drive power provided by the frequency converter 24 (see Fig. 2). In this case, the provided drive power is typically insufficient to keep the set compressor speed 27 constant due to the work performed by the compressor on the laser gas 4.In particular, the pressure generated on the downstream side of the compressor impeller 23 by the compressor work causes the compressor impeller 23 to slow down. Preferably, the supply of drive power is reduced or even stopped, at least temporarily. This can result in a significant reduction in the compressor speed 27, allowing the maintenance procedure 25 to be carried out more precisely.

[0058] The compressor impeller 23, which rotates when the drive power is reduced or interrupted, can induce voltages in the frequency converter 24 by rotating the electric drive unit 22. These induced voltages can be detected and assigned to a specific compressor speed 27. This allows the compressor speed 27 of the electric compressor 23 to be determined. Alternatively or additionally, the compressor speed 27 can be detected, for example, using a Hall sensor.

[0059] Preferably, the compressor speed 27 is reduced to a predetermined minimum speed 28 of the electric compressor 7. A minimum speed of the electric compressor 7 can, for example, be a standby speed or a complete standstill. A standby speed can be understood as a ready speed, for example, in a sleep mode of the CO2 laser system 1. Such a mode reduces energy consumption during periods of inactivity. Furthermore, this mode reduces the pressure before and after the compressor impeller 23. A complete standstill can be understood as switching off the CO2 laser system 1, whereby the compressor impeller 23 comes to a complete stop. In other words, the electric compressor 7 is allowed to coast to a stop.By reducing the compressor speed 27 in this way, the maintenance procedure 25 can be particularly advantageously integrated into the normal operating cycle of the electric compressor 7. An unscheduled execution of the maintenance procedure 25 can be dispensed with.

[0060] In a subsequent process step 29 of the maintenance procedure 25, the compressor speed 27 of the electric compressor 7 is measured as a function of time 30. In other words, the decrease in the compressor speed 7 within a predetermined time period is measured. Typically, the decrease in speed is measured in a delay curve 31 (see Fig. 4).

[0061] In a particular embodiment, the compressor speed 27 can be reduced and / or monitored over a predetermined delay period. If a delay period is specified, the maintenance procedure 25 can be carried out by briefly interrupting the operation of the CO2 laser system 1. This allows the number of checks to be increased. Preferably, the delay period is at least 50 seconds, more preferably at least 100 seconds, and particularly preferably at least 150 seconds.

[0062] Alternatively, it can be provided that the time 30 until the minimum rotational speed 28 is reached is determined.

[0063] A further process step 32 of the maintenance procedure 25 involves comparing the speed reduction of the electric compressor 7 with at least one stored reference speed reduction 33 (see Fig. 4). In other words, the deceleration curve 31 can be compared with one or more reference speed reductions 33. This makes it possible to determine deviations of the recorded deceleration curve 31 from the expected speed reductions of the electric compressor 7.

[0064] The reference speed reduction 33 can, for example, be stored as at least one speed gradient 34 and / or as at least one speed characteristic curve 35.

[0065] The at least one reference speed reduction 33 is preferably stored as a reference measurement of the same electric compressor 7. This allows compressor-specific manufacturing differences to be taken into account during the evaluation and deviations to be detected more quickly.

[0066] A comparison of the speed reduction with at least one reference speed reduction 33 is preferably carried out automatically by maintenance software not shown in detail. This allows the maintenance procedure 25 to be performed particularly independently of operator intervention.

[0067] In a further process step 36 of the maintenance procedure 25, a maintenance recommendation is issued based on the comparison from process step 32. The maintenance recommendation typically includes a statement and / or a note regarding maintenance work to be carried out on the electric compressor 7. This allows maintenance on the electric compressor 7 to be planned and carried out in a timely manner. Unforeseen failures of the electric compressor 7 in conjunction with a failure of the CO2 laser system 1 can thus be effectively prevented.

[0068] Preferably, the maintenance recommendation includes the comparison and / or the results from the comparison in process step d) and / or a determined current state of the electric compressor 7. In particular, the maintenance recommendation includes information on the current state of the electric drive unit 22, or the electric motor.

[0069] The maintenance recommendation particularly preferably includes a note on the urgency of maintenance of the electric compressor 7, especially the electric drive unit 22.

[0070] Particularly advantageous is the additional process step 37 in the maintenance procedure 25, which involves lowering the pressure downstream of the compressor impeller 23 of the electric compressor 7. Lowering the downstream pressure at the compressor impeller 23 prevents excessive deceleration of the impeller 23, thus allowing the maintenance procedure 25 to be carried out more precisely. Furthermore, high pressure at the downstream side of the compressor impeller 23 can lead to excessive stress on the electric compressor 7. Therefore, process step 30 is typically performed before process step 26, enabling the maintenance procedure 25 to be carried out more precisely while protecting the components of the electric compressor 7.

[0071] Preferably, the pressure downstream of the compressor impeller 23 is reduced to the ambient pressure of the CO2 laser system 1. This can be achieved, for example, by using a pump (not shown), in particular a vacuum pump, to pump out the pressure generated by the electric compressor 7 and / or by means of appropriately arranged or designed drain valves (not shown) on the downstream side of the compressor impeller 23.

[0072] Fig. 4 schematically shows an exemplary speed reduction or deceleration curve 31, as can be recorded when reducing the compressor speed 27 according to the preceding maintenance procedure 25 (see Fig. 3).

[0073] Starting from an operating speed 38 of the electric compressor 7 (see Figs. 1, 2), the compressor speed 27 is reduced by lowering the drive power. The reduction in speed of the electric compressor 7 can be measured according to the deceleration curve 31 shown. The deceleration curve 31 records the change in the compressor speed 27 down to a minimum speed 28, for example, a standstill of the compressor impeller 23 (see Fig. 2).

[0074] The compressor speed 27 is shown over time 30. The deceleration curve 31 is shown up to a final time 39, at which the minimum speed 28 is reached.

[0075] Fig. 4 further shows several, here three, reference speed reductions 33. The reference speed reductions 33 are, as shown, represented as a speed gradient 34, a first speed characteristic curve 35a and a second speed characteristic curve 35b. The speed characteristic curve 35a has an end time 40 and the speed characteristic curve 35b an end time 41.

[0076] A comparison of the deceleration curve 31 can, for example, involve a comparison with the course of a reference speed characteristic curve 35a, 35b and / or a comparison with several, in particular all, reference speed characteristic curves 35a, 35b. As shown, the deceleration curve 31 exhibits a greater reduction in speed than the reference speed characteristic curves 35a, 35b. In other words, the final time 39 occurs before the final times 40, 41.

[0077] The inventors recognized that a deteriorated condition of the electric compressor 7, or the electric drive unit 22 (see Fig. 2), can lead to internal short circuits and high electromagnetic losses, which cause increased braking of the compressor impeller 34. Therefore, the actual condition of the electric compressor 7, or the electric drive unit 22, can be determined by changing the speed reduction.

[0078] Alternatively or additionally, it can be provided that a maximum speed gradient of the deceleration curve 31 is compared with the stored speed gradient 34. This allows the maintenance procedure 25 to be carried out in a shorter period of time.

[0079] ist

[0080] 1 CO2 laser system; 24 frequency converters;

[0081] 2 Laser resonator; 25 25 Maintenance procedures;

[0082] 3 discharge tubes; 26 process steps;

[0083] 4 laser gas; 27 compressor speed;

[0084] 5 electrodes; 28 minimum speed;

[0085] 6 Laser beam; 29 Process step;

[0086] 6' Part of the laser beam 6; 30 30 Time;

[0087] 7 electric compressors; 31 delay curve;

[0088] 8 Feed arm; 32 Process step;

[0089] 9, 9' second feed element; 33 reference-

[0090] 10. First discharge element; speed reduction;

[0091] 11 Discharge arm; 35 34 Speed ​​gradient;

[0092] 12 first level; 35 speed characteristic curve;

[0093] 13 second level; 35a first speed characteristic curve;

[0094] 14 Deflection mirror; 35b second speed characteristic curve;

[0095] 15, 16 Resonator mirrors; 36 Procedure step;

[0096] 17 Sub-area; 4o 37 Procedure step;

[0097] 18 Catalyst; 38 Operating speed;

[0098] 19 Dissociation product; 39 End time;

[0099] 21 Lockable opening; 40, 41 End time;

[0100] 22 electric drive unit; K laser gas circuit.

[0101] 23 Compressor impeller;

Claims

Patent claims 1. Maintenance method (25) for monitoring and maintaining electric compressors (7), in particular for circulating a laser gas (4) in a CO2 laser system (1), comprising the process steps: b) reducing (26) a compressor speed (27) of the electric compressor (7) by changing a drive mode of an electric drive unit (22) of the electric compressor (7) to a generator mode; c) determining a speed reduction by recording (32) the compressor speed (27) as a function of time (30); d) comparing (36) the speed reduction, in particular a deceleration curve (31), with at least one stored reference speed reduction (33); e) outputting (37) a maintenance recommendation as a function of the comparison from process step d).

2. Maintenance method (25) according to claim 1, comprising the additional method step a): lowering a pressure downstream of a compressor impeller (23) of the electric compressor (7); wherein method step a) is performed before method step b).

3. Maintenance method (25) according to claim 2, wherein the pressure is reduced to an ambient pressure.

4. Maintenance method (25) according to one of the preceding claims, wherein the reference speed reduction (33) is stored as at least one speed gradient (34) and / or as at least one speed characteristic curve (35; 35a, 35b).

5. Maintenance method (25) according to claim 4, wherein a plurality of Speed ​​characteristics (35; 35a, 35b) are stored.

6. Maintenance method (25) according to one of the preceding claims, wherein the reference speed reduction (33) is stored as a reference measurement of the same electric compressor (7).

7. Maintenance method (25) according to one of the preceding claims, wherein the compressor speed (27) is reduced over a predetermined delay period.

8. Maintenance method (25) according to claim 7, wherein the delay period is at least 50 seconds, preferably at least 100 seconds, particularly preferably at least 150 seconds.

9. Maintenance method (25) according to one of the preceding claims, wherein the compressor speed (27) is reduced to a predetermined minimum speed (28).

10. Maintenance method (25) according to claim 9, wherein the minimum speed (28) is predetermined as a standby speed of the electric compressor or as a standstill of the electric compressor (7).

11. Maintenance method (25) according to one of the preceding claims, wherein method step d) is carried out automatically by maintenance software.

12. Maintenance method (25) according to one of the preceding claims, wherein the maintenance recommendation comprises the comparison from method step d) and / or a determined actual state of the electric compressor (7), in particular the electric drive unit (22).

13. Maintenance method (25) according to one of the preceding claims, wherein the maintenance recommendation includes an indication of the urgency of maintenance of the electric compressor (7), in particular the electric drive unit (22).

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