Drive unit assembly for a vacuum pump system,vacuum pump system and method

Abstract

A vacuum pump system (100, fig.1) comprises two pumps 110, 120 and a motor drive assembly 130 mounted in an enclosure 140. In prior art, it is known to mount a drive assembly vertically in an enclosu

Description

The field of the invention relates to vacuum pumps, and more specifically to drive units for vacuum pump systems. BACKGROUND Vacuum pumps are typically employed as a component of a vacuum pump system to evacuate working gases from the system. One or more of these pumps can be used to evacuate fabrication equipment used in, for example, the production of semi-conductors. Whilst compression from a vacuum to atmosphere may be performed in a single stage using a single pump, it is common in such applications to provide multi-stage vacuum pumps wherein each stage performs a portion of the compression range required to transition from a vacuum to atmospheric pressure. Vacuum pumps may include dry pumps and booster pumps, as non-limiting examples. Conventionally, vacuum pumps are driven by electric motors. The motors typically receive electrical power from an alternating current (AC) grid power source. A drive unit for a motor of a vacuum pump will typically rectify this AC electrical input power in order to generate direct current (DC) power that can be smoothed and inverted to provide an AC output power with the necessary frequency and voltage for driving the motor of the vacuum pump. The electronics that receive the AC input power, perform the inversion, the smoothing, the rectification, and then output the AC output power for the motors, are typically provided on printed circuit boards (PCBs). Existing drive units for vacuum pump systems tend to be mounted having their elongate dimension extending vertically. This allows for easier connection to peripherals such as sources of electrical power and motors. More specifically, the vertical mounting arrangement allows for electrical connections using wires or cables that extend largely linearly from peripherals of the vacuum pump system to the required electrical connections in the drive units. However, there is an increasing desire to provide more compact and spatially compliant vacuum pump systems. Vertically mounted drive units are not always achievable for a given footprint or spatial limitation within such a system. In order to meet such footprint / spatial limitations, drive units may be required to be mounted having their elongate dimension aligned horizontally. To connect horizontally mounted drive units to peripherals of the vacuum pump system such as sources of electrical power and motors, wires / cabling tends to be required to navigate a path having relatively abrupt changes in direction. This is particularly the case where the wires / cabling must navigate a change in direction of 90° (i.e., from vertical to horizontal) in order to achieve an interface with the drive unit itself. This tends to place a curvature on the wires / cables that breaches the maximum permitted radius of curvature of the wires / cabling (which is generally considered to be 6 times the diameter of the cable / wire). If achievable at all, this can lead to excessive wear and damage of the wires / cabling and their connection points, ultimately affecting reliability and leading to increased servicing and maintenance costs. Hence, there is a need to provide an alternative mechanism for electrically connecting a drive unit in a vacuum pump system that mitigates these issues. SUMMARY OF THE INVENTION In a first aspect, there is provided a drive unit assembly for a vacuum pump system, the drive unit assembly comprising a first drive unit comprising: a first casing containing a first circuit for driving a first motor of a first vacuum pump, the first circuit having a first alternating current, AC, input and a first AC output; one or more first bus bars connected to the first AC input, the one or more first bus bars being arranged to extend outwardly of the first casing to or beyond an exterior side of the first casing for connecting to one or more first cables and / or wires of the vacuum pump system; and one or more second bus bars connected to the first AC output, the one or more second bus bars being arranged to extend outwardly of the first casing to or beyond the exterior side of the first casing for connecting to one or more second cables and / or wires of the vacuum pump system. In vacuum pump systems, drive units tend to be mounted in a vertical configuration (i.e., having their elongate dimension extending vertically) permitting cabling and / or wiring of the vacuum pump system to navigate a substantially linear path to connect with the drive unit. However, some vacuum pump systems require horizontally mounted drive units which changes the geometry of how cabling and / or wiring of a vacuum pump system connects to the drive units. Specifically, the change in geometry from vertical to horizontal orientation tends to require abrupt changes in direction of cables and / or wires particularly at the point of connection to the drive unit. For example, cables and / or wires extending parallel an exterior side of a drive unit tend to be required to navigate a sharp 90° turn to enter the drive unit and electrically connect to the electrical circuit contained therein. This sharp turn tends to force the cables / wires into a radius of curvature beyond the recommended limit of six times the diameter of the cable / wire. This tends to place excessive strain on the cables / wires and their connections, leading to excessive wear and damage and ultimately failure of the cables / wires and connections. Currently, the alternative to avoid such issues is to provide larger radiuses of curvature, impacting the spatial footprint of the vacuum pump system. In some system designs, these larger radiuses of curvature are simply no achievable. The inventors have found that it is possible to mitigate these issues and provide a drive unit assembly can be electrically connected to an AC power supply and other components / peripherals of a vacuum pump system (such as electrical motors and / or heater elements) without breaching the maximum bend radius of wires and / or cables of the vacuum pump system. The inventors have found that providing bus bars in a drive unit that extend to or beyond an exterior surface of the drive unit tends to allow for cables / wires of the vacuum pump system to extend substantially parallel the exterior surface and abut or connect with the bus bars without a need for sharp curves or turns in the cables / wires to interface with the drive unit assembly. This tends to maintain the advantageous linear path of cabling / wiring present in vacuum pump systems comprising vertically mounted drive units, even in vacuum pump systems wherein the drive units are mounted horizontally. Furthermore, this tends to provide a decreased spatial footprint of the cabling / wiring. The bus bars extend ‘to or beyond’ the exterior surface to enable such an electrical connection. This may comprise the bus bars defining an overhang or similar against which the cables / wires can connect. Alternatively the bus bars may themselves comprise a curved portion allows the bus bars to exit the casing and then extend along the exterior surface of the casing. Alternatively the bus bars may extend to the exterior surface i.e., flush with the exterior surface, to provide a point for abutment and electrical connection. The one or more first bus bars and one or more second bus bars may extend beyond the same or different exterior sides of the first casing. The one or more first cables and / or wires and one or more second cables and / or wires of the vacuum pump system may extend parallel the exterior side to meet with / connect to the respective one or more first bus bars and one or more second bus bars. The cables and or wires may for instance extend vertically and parallel the exterior side. The one or more first bus bars may extend linearly beyond the exterior side of the first casing; and / or the one or more second bus bars extend linearly beyond the exterior side of the first casing. By extending linearly beyond the exterior side of the first casing, the bus bars define an overhang substantially perpendicular to the exterior side of the first casing. Cables and / or wiring of the vacuum pump system can hence extend substantially linearly and parallel the exterior surface to abut the bus bars and connect therewith without any abrupt changes, curves, or turns, in the path of the cables / wires. The one or more first bus bars may extend around an edge of the first casing to extend along the exterior side of the first casing; and / or the one or more second bus bars may extend around an edge of the first casing to extend along the exterior side of the first casing. By extending around an edge of the first casing and extending along the exterior side of the first casing, part of the bus bars extends substantially parallel to the exterior side. Cables and / or wiring of the vacuum pump system can hence extend substantially linearly and parallel the exterior surface against the bus bars and connect therewith without any abrupt changes, curves, or turns, in the path of the cables / wires. Furthermore, electrical connections can be provided on the bus bars exterior to the drive unit assembly into which wires / cabling can be received. The one or more first bus bars may comprise three bus bars; and the one or more second bus bars may comprise three bus bars. By providing three of the first bus bars and three of the second bus bars, the drive unit can receive three-phase AC power from a three-phase AC power source / supply and provide three-phase AC power to the motor of the vacuum pump. The one or more first bus bars and the one or more second bus bars may comprise copper. Copper is an electrically conductive material that can be easily shaped and cut to provide the desired configuration of the bus bars. The one or more first bus bars and the one or more second bus bars may be substantially flat. Substantially flat bus bars further optimise the spatial size (i.e., volume and footprint) of the drive unit assembly. The one or more first bus bars may comprise one or more first ring terminal connections exterior to the first casing for connecting to the one or more first cables and / or wires; and / or the one or more second bus bars may comprise one or more second ring terminal connections exterior to the first casing for connecting to the one or more second cables and / or wires. Ring terminal connections can be a requirement for power cable connections in some specifications. The first casing may comprise a first top cover, a first middle cover, and a first bottom cover. The one or more first bus bars and one or more second bus bars may be arranged between the first top cover and the first middle cover. The first circuit may be arranged between the first middle cover and the first bottom cover. The first top cover and / or first middle cover may comprise: one or more first channels for receiving respective first bus bars of the one or more first bus bars; and one or more second channels for receiving respective second bus bars of the one or more second bus bars. The first channels and second channels tend to retain and hold the respective first bus bars and second bus bars in electrical isolation from each other. The first middle cover, the one or more first bus bars, and the one or more second bus bars may comprise one or more collocated holes; wherein electrically conductive bolts are arranged through the collocated holes for electrically connecting the one or more first bus bars and one or more second bus bars to the first circuit. The collocated holes and electrically conductive bolts tend to provide the electrical connection between the busbars and the first circuit. One or more nuts may be used to fasten the first middle cover and the one or more first bus bars together. Similarly, one or more nuts may be used to fasten the first middle cover and the one or more second bus bars together. The first circuit may comprise a first printed circuit board. The first printed circuit board may also comprise one or more of the collocated holes for providing the electrical connectivity to the one or more electrically conductive bolts. The first casing may comprise plastic. Plastic is a suitable electrical insulator that can be readily moulded into the required configuration for the drive unit assembly. The drive unit assembly may further comprise a second drive unit, the second drive unit comprising: a second casing containing a second circuit for driving a second motor of a second vacuum pump, the second circuit having a second AC input and a second AC output; one or more third bus bars connected to the second AC output, the one or more third bus bars extending outwardly of the second casing to or beyond an exterior side of the second casing for connecting to one or more third cables and / or wires of the vacuum pump system; wherein the drive unit assembly further comprises one or more interconnecting bus bars connected between the one or more first bus bars and the second AC input, such that the first AC input and the second AC input are electrically connected in parallel. The one or more interconnecting bus bars tend to provide electrical connectivity from an AC input power of the first drive unit, to the second drive unit. Therefore a single AC power supply / source tends to power both drive units (i.e., provides power to both drive units in parallel). The one or more interconnecting bus bars may overlap the one or more first bus bars to further reduce the spatial profile of the drive unit. The second drive unit may further comprise one or more fourth bus bars connected to the second AC output, the one or more fourth bus bars extending outwardly of the second casing to or beyond an exterior side of the second casing for connecting to one or more fourth cables and / or wires of the vacuum pump system. The one or more fourth cables and / or wires may, for instance, be cables connected to a heater module of the vacuum pump system. Hence the second drive unit can be configured to output AC power to a heater module in addition to a motor of a second vacuum pump. The one or more fourth cables and / or wires may alternatively originate from other modules or peripherals of the vacuum pump system. The one or more fourth bus bars provide additional power connectivity for other modules / peripherals of the vacuum pump system. According to a second aspect, there is provided a vacuum pump system comprising: one or more vacuum pumps; and the drive unit assembly of the first aspect. According to a third aspect, there is provided a method of electrically connecting a drive unit assembly to a vacuum pump system, the method comprising: providing the drive unit assembly of the first aspect; arranging one or more first cables and / or wires of the vacuum pump system to extend substantially parallel the exterior side of the first casing of the drive unit assembly; connecting the one or more first cables and / or wires to the one or more first bus bars at a position where the one or more first bus bars extend to or beyond the exterior side of the first casing; arranging one or more second cables and / or wires of the vacuum pump system to extend substantially parallel the exterior side of the first casing of the drive unit assembly; and connecting the one or more second cables and / or wires to the one or more second bus bars at a position where the one or more second bus bars extend to or beyond the exterior side of the first casing. It will be appreciated that the particular features of different aspects of the invention tend to share the technical effects and benefits of corresponding features of other aspects of the invention. More specifically, the vacuum pump system and methods described herein share the same technical benefits as the drive unit assembly described herein. It will also be appreciated that the use of the terms “first” and “second”, and the like, are merely intended to help distinguish between similar features and are not intended to indicate a relative importance of one feature over another, unless otherwise specified. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1A shows an example of a vacuum pump system comprising a horizontally mounted drive unit assembly; Figure 1B shows the vacuum pump system of Figure 1A in a side view; Figure 2A shows an example, in perspective view, of a drive unit assembly; Figure 2B shows an example, in exploded view, of the drive unit assembly of Figure 2A; Figure 2C shows an example, in perspective view, of the drive unit assembly of Figure 2A with top cover removed; Figure 2D shows an example of a top cover of a casing as used in the drive unit assembly of Figure 2A; Figure 2E shows an example of a middle cover of a casing as used in the drive unit assembly of Figure 2A; and Figure 3 shows an example of a method of electrically connecting a drive unit assembly to a vacuum pump system. DETAILED DESCRIPTION Figure 1A shows an example, in perspective view, of a vacuum pump system 100. The vacuum pump system 100 comprises a first vacuum pump 110 and a second vacuum pump 120. The vacuum pump system 100 further comprises a drive unit assembly 130. The first vacuum pump 110 and the second vacuum pump 120 are vertically stacked inside a system casing 140. The drive unit assembly 130 is mounted atop the vacuum pumps 110, 120 and extends horizontally. The system casing 140 defines the internal volume available for the first vacuum pump 110, second vacuum pump 120, the drive unit assembly 130 and other peripherals. As is evident from the figure, the spatial footprint and volume available within the system casing 140 is limited. Figure 1B shows the vacuum pump system 100 of Figure 1A in a side view. The Figure shows the first vacuum pump 110, drive unit assembly 130 and system casing 140. As is evident from the figure, it is not achievable to mount the drive unit assembly 130 having its elongate dimension extending vertically. In this regard, the spatial footprint / volume defined by the system casing 140 does not provide sufficient area / volume for receiving the drive unit assembly 130 vertically. Thus the drive unit assembly 130 must be mounted horizontally extending across the top of the first vacuum pump 110. Figure 1B shows voids 150 between the first vacuum pump 110 and system casing 140 and between the drive unit assembly 130 and system casing 140. These voids 150 allow for wires / cabling of the first vacuum pump 110 and other components / peripherals of the system 100 to extend to the drive unit assembly 130 for electrical connection to the drive unit assembly 130. Proximal the drive unit assembly 130, the void 150 has a size of approximately 24mm when measured between the system casing 140 and the drive unit assembly 130. In the system 100 it is not possible to curve a wire / cable extending from first vacuum pump 110 through void 150 to electrically connect with drive unit assembly 130. To do so would exceed the maximum bend radius of the wire / cable. The maximum bend radius (typically six times the diameter of the wire / cable) is set so as to mitigate damage and performance reduction to / of the wire / cable. To overcome this issue an alternative configuration of the drive unit assembly 130 has been provided which will be discussed herein in greater detail. Drive unit assemblies and their function will be introduced generally. A drive unit assembly typically comprises a drive circuit (also referred to herein as a circuit) that provides power and control to a motor of a vacuum pump. The power provided to the motor of a vacuum pump is an AC electrical power that has been optimised by the drive circuit for the particular motor. More specifically, the drive unit assembly receives an input AC electrical power from an AC power source (such as an AC power grid), rectifies the input AC electrical power to generate a DC electrical power, smooths the DC electrical power, and then inverts the smoothed DC electrical power to provide an output AC electrical power with the necessary frequency and voltage for driving the motor of the vacuum pump. Generally, a drive unit assembly comprises one or more drive units each having an electrical circuit comprising a rectifier for converting AC input power to a DC power, and an inverter for converting the DC power to an AC output power. More specifically, the rectifier may be a diode bridge rectifier that has an AC electrical input for connection to each phase of a three-phase AC power supply. The diode bridge rectifier converts the received AC electrical input power to a DC electrical power which is output by the rectifier. The diode bridge rectifier may be of the ‘6-pulse type’ for instance, wherein two diodes are provided for each phase of the three-phase AC power supply. Larger diode bridge rectifiers also exist, such as those comprising twelve or eighteen diodes. A drive unit assembly typically comprises a DC electrical link electrically connecting the output of the diode bridge rectifier to an input of the electrical inverter. The electrical inverter is configured to receive the DC electrical power and to convert the DC electrical power to an AC electrical output power for driving the motor of the vacuum pump. The electrical inverter tends to be electrically connected to the motor of the vacuum pump for each phase of AC electrical output power i.e., using three-phase connections. The motor of the vacuum pump (which may be an induction or permanent magnet motor) can thus be driven according to the necessary frequency and voltage AC power. Electrical filters and chokes may also be used in the drive unit assembly electrical circuits to smooth electrical signals. With the general understanding of drive unit assemblies hereinbefore discussed, an advantageous implementation of a drive unit assembly within a vacuum pump system will now be described. Figure 2A shows an example, in perspective view, of a drive unit assembly 200 for a vacuum pump system. The drive unit assembly 200 comprises a first drive unit 210 and a second drive unit 220. The first drive unit 210 is for driving a motor of a first vacuum pump. The second drive unit 220 is for driving a motor of a second vacuum pump. The drive unit assembly 200 may be the drive unit assembly 130 of Figure 1. Each of the drive units 210 and 220 may have dimensions 3350mm by 150mm by 100mm or less (i.e., approximately 3310mm by 140mm by 100mm). Figure 2B shows, in exploded view, the drive unit assembly 200 of Figure 2A. The exploded view of the drive unit assembly 200 shows the first drive unit 210 and second drive unit 220. The first and second drive units 210, 220 will now be described. The first drive unit 210 comprises a first casing 211 (211 a, 211 b, 211 c). The first casing 211 comprises a first top cover 211a, a first middle cover 211b, and a first bottom cover 211c. The first casing 211 comprises plastic. The first casing 211 contains a first circuit 212 for driving a first motor of a first vacuum pump, the first circuit 212 has a first AC input and a first AC output. The first circuit 212 is arranged between the first middle cover 211b and the first bottom cover 211c. The first drive unit 210 comprises one or more first bus bars 213 connected to the first AC input of the first circuit 212. The one or more first bus bars 213 are arranged to extend outwardly of the first casing 211 to or beyond an exterior side of the first casing 211. The one or more first bus bars 213 are for connecting to one or more first cables and / or wires of a vacuum pump system. More specifically, the one or more first bus bars 213 comprise three bus bars. The first drive unit 210 comprises one or more second bus bars 214 connected to the first AC output of the first circuit 212. The one or more second bus bars 214 are arranged to extend outwardly of the first casing 211 to or beyond the exterior side of the first casing 211. The one or more second bus bars 214 are for connecting to one or more second cables and / or wires of a vacuum pump system. More specifically, the one or more second bus bars 214 comprise three bus bars. The one or more first bus bars 213 and one or more second bus bars 214 are arranged between the first top cover 211a and the first middle cover 211 b. The one or more first bus bars 213 and the one or more second bus bars 214 comprise copper and are substantially flat. The second drive unit 220 of the drive unit assembly 200 largely resembles the first drive unit 210. The second drive unit 220 comprises a second casing 221 (221a, 221b, 221c) having a top cover 221a, middle cover 221b and bottom cover 221c. The second casing 221 also comprises plastic and contains a second circuit 222 for driving a second motor of a second vacuum pump. The second circuit 222 has a second AC input and a second AC output. One or more third bus bars 223 connect to the second AC output. The one or more third bus bars 223 extend outwardly of the second casing 221 to or beyond an exterior side of the second casing 221 for connecting to one or more third cables and / or wires of a vacuum pump system. More specifically, the one or more third bus bars 223 comprise three bus bars. The drive unit assembly 200 further comprises one or more interconnecting bus bars 224 connected between the one or more first bus bars 213 and the second AC input of the second circuit 222, such that the first AC input of the first circuit 212 and the second AC input of the second circuit 222 are electrically connected in parallel. More specifically, the interconnecting bus bars 224 comprise three interconnecting bus bars. The second drive unit 220 further comprises one or more fourth bus bars 225 connected to the second AC output of the second circuit 222. The one or more fourth bus bars 225 extend outwardly of the second casing 221 to or beyond an exterior side of the second casing 221 for connecting to one or more fourth cables and / or wires of the vacuum pump system. More specifically, the one or more fourth bus bars 225 comprise three bus bars. The one or more third bus bars 223 and the one or more fourth bus bars 225 are arranged between second top cover 221a and the second middle cover 221b. The interconnecting bus bars 224 are arranged between the top covers 211a, 221a and the middle covers 211b, 221b. The one or more third bus bars 223, the one or more fourth bus bars 225 and the interconnecting bus bars 224 comprise copper and are substantially flat. Figure 2C shows, in perspective view, the drive unit assembly 200 of Figure 2A with top covers 211a, 221a removed. The first drive unit 210 is shown with first middle cover 211b visible. Seated into the first middle cover 211b are the three bus bars of the one or more first bus bars 213. The one or more first bus bars 213 extend horizontally and then around an edge 211 b1 of the first middle cover 211 b towards a vertical orientation. The one or more first bus bars 213 then extend vertically along the exterior side of the first middle cover 211b. The one or more first bus bars 213 comprise one or more first ring terminal connections 213a exterior to the first middle cover 211 b for connecting to the one or more first cables and / or wires of the vacuum pump system. The one or more first ring terminal connections 213a receive the one or more first cables and / or wires substantially parallel the exterior side (i.e., substantially vertically) and hence tend to not require bends or curves in the first cables and / or wires. The first cables and / or wires provide the means through which AC input power is provided to the drive unit assembly 200. Also seated into the first middle cover 211 b are the three bus bars of the one or more second bus bars 214. The one or more second bus bars 214 extend horizontally and then around the edge 211 b1 of the first middle cover 211b towards a vertical orientation. The one or more second bus bars 214 then extend vertically along the exterior side of the first middle cover 211b. The one or more second bus bars 214 comprise one or more second ring terminal connections 214a exterior to the first middle cover 211b for connecting to one or more second cables and / or wires of the vacuum pump system. The one or more second ring terminal connections 214a receive the one or more second cables and / or wires substantially parallel the exterior side (i.e., substantially vertically) and hence tend not to require bends or curves in the second cables and / or wires. The second cables and / or wires are the cables / wires providing the means through which AC power from the first drive unit 210 is provided to a motor of a first vacuum pump of the vacuum pump system. The second drive unit 212 is shown with second middle cover 221b visible. Seated into the second middle cover 221b are the three bus bars of the one or more third bus bars 223. The one or more third bus bars 223 extend horizontally and then around an edge 221 b1 of the second middle cover 221b towards a vertical orientation. The one or more third bus bars 223 then extend vertically along the exterior side of the second middle cover 221b. The one or more third bus bars 223 comprise one or more third ring terminal connections 223a exterior to the second middle cover 221b for connecting to the one or more third cables and / or wires of the vacuum pump system. The one or more third ring terminal connections 223a receive the one or more third cables and / or wires substantially parallel the exterior side (i.e., substantially vertically) and hence tending to not require bends or curves in the third cables and / or wires. The third cables and / or wires are those which provide the means through which AC output power from the second drive unit 220 of the drive unit assembly 200 is provided to a second motor of a second vacuum pump of the vacuum pump system. Also seated into the second middle cover 221b are the three bus bars of the one or more fourth bus bars 225. The one or more fourth bus bars 225 extend horizontally and then around the edge 221 b1 of the second middle cover 221b towards a vertical orientation. The one or more fourth bus bars 225 then extend vertically along the exterior side of the second middle cover 221b. The one or more fourth bus bars 225 comprise one or more fourth ring terminal connections 225a exterior to the second middle cover 221b for connecting to one or more fourth cables and / or wires of the vacuum pump system. The one or more fourth ring terminal connections 225a receive the one or more fourth cables and / or wires substantially parallel the exterior side (i.e., substantially vertically) and hence tending not to require bends or curves in the fourth cables and / or wires. The fourth cables and / or wires are the cables / wires providing the means through which AC power is provided from the second drive unit 220 of the drive unit assembly 200 to heating means or another peripheral of the vacuum pump system. Located atop the one or more first bus bars 213 and the one or more fourth bus bars 225 are the interconnecting bus bars 224 providing electrical connection between respective busbars of the one or more first bus bars 213 and the one or more fourth bus bars 225. More specifically, the bus bar of the one or more first bus bars 213 that itself is connected to a first phase of an AC input power, is also connected to the bus bar of the one or more fourth bus bars 225 requiring connection to the same electrical phase. This connection is achieved by one of the interconnecting bus bars 224. Such an electrical configuration is established for each of the three bus bars of the first bus bars 213 and fourth bus bars 225. In this manner the first bus bars 213 and fourth bus bars 225 are electrically connected in parallel with the three phase AC input power received via first ring terminal connections 213a. Also visible are holes 230 in the middle covers 211 b, 221 b, the one or more second bus bars 214 and the one or more third bus bars 223. Similar holes are also present (but not shown in the figure) in the one or more first bus bars 213, one or more fourth bus bars 225 and the interconnecting bus bars 224. The holes 230 in the middle covers 211 b, 221b are collocated with the holes 230 in the respective bus bars 213, 214, 222, 224, 225. Electrically conductive bolts 235 are arranged through the collocated holes 230 for electrically connecting the bus bars 213, 214, 222, 224, 225 to the first and second circuits (not visible). Figure 2D shows an example of a top cover 211a of a casing 211 as used in the drive unit assembly 200 of Figure 2A. The top cover 211a is inverted relative to Figure 2A to allow for the underside of the top cover 211a to be shown. The top cover 211a is substantially planar and comprises one or more first channels 211a1 for receiving respective bus bars of the one or more first bus bars 213 of the first drive unit 210. The channels 211a1 are defined by ridges extending from the planar surface of the underside of the top cover 211a. The channels 211a1 assist in both retaining the bus bars 213 and in achieving electrical isolation between the bus bars 213. Figure 2E shows an example of a middle cover 211b of a casing 211 as used in the drive unit assembly 200 of Figure 2A. The middle cover 211b is substantially planar and comprises one or more first channels 211b2 for receiving respective bus bars of the one or more first bus bars 213 of the drive unit 210. The channels 211b2 are defined by ridges extending from the planar surface of the middle cover 211b. The channels 211b2 assist in both retaining the bus bars 213 and in achieving electrical isolation between the bus bars 213. The middle cover 211b also comprises one or more second channels 211b3 for receiving respective bus bars of the one or more second bus bars 214 of the drive unit 210. The channels 211b3 are defined by ridges extending from the planar surface of the middle cover 211b. The channels 211b3 assist in both retaining the bus bars 214 and in achieving electrical isolation between the bus bars 214. Figure 3 shows an example of a method 300 of electrically connecting a drive unit assembly to a vacuum pump system. The drive unit assembly may be the drive unit assembly 200 of Figure 2 or one of the drive units 210, 220 of Figure 2, for instance. The vacuum pump system may be the system 100 of Figure 1. The method 300 shall be described with reference to features of the drive unit assembly 200. A first step 310 comprises providing the drive unit assembly 200 of the first aspect. A further step 320 comprises arranging one or more first cables and / or wires of the vacuum pump system to extend substantially parallel the exterior side of the first casing 211 of the drive unit assembly 200. A further step 330 comprises connecting the one or more first cables and / or wires to the one or more first bus bars 213 at a position 213a where the one or more first bus bars 213 extend to or beyond the exterior side of the first casing 211. A further step 340 comprises arranging one or more second cables and / or wires of the vacuum pump system to extend substantially parallel the exterior side of the first casing 211 of the drive unit assembly 220. A further step 350 comprises connecting the one or more second cables and / or wires to the one or more second bus bars 214 at a position 214a where the one or more second bus bars 214 extend to or beyond the exterior side of the first casing 211. In-use the first cables / wires transport an input AC electrical power from an AC power supply to the first drive unit 210 of the drive unit assembly 200. More specifically, the input AC electrical power is provided to first bus bars 213. The input AC electrical power it received by first circuit 212 via the first bus bars 213. The first circuit 212 performs rectification of the input AC electrical power to a DC electrical power. The first circuit 212 inverts the DC electrical power to an output AC electrical power of a predetermined frequency and voltage. The first circuit 212 provides the output AC electrical power to second bus bars 214. The second bus bars 214 transport the output AC electrical power to second cables / wires connected at connections 214a. The second cables / wires transport the output AC electrical power to a first motor of a first vacuum pump. Whilst the flow of electrical power is described with respect to the first drive unit 210, a similar flow of electrical power can be described for the second drive unit 220. Specifically, the interconnecting bus bars 224 electrically connects the second circuit 222 of second drive unit 220, to the input AC electrical power. The second circuit 222 performs rectification and inversion in accordance with the first circuit 212. The second circuit 222 outputs an AC electrical power to third bus bars 223. The third bus bars 223 transport said AC electrical power to third cables / wires connected at connections 223a. The third cables / wires transport said AC electrical power to a second motor of a second vacuum pump. Furthermore, the interconnecting bus bars 224 electrically connects the fourth bus bars 225 to the input AC electrical power. This allows other peripherals, such as heating elements, to be powered via connections 225a. Whilst specific examples described herein show vacuum pump systems having a certain quantity of vacuum pumps, this is not intended to be limiting. Vacuum pump systems may comprise one or more vacuum pumps. Whilst specific examples described herein show first and second drive units 210, 220 in a drive unit assembly 200, other drive unit assemblies may comprise a single drive unit (i.e., drive unit 210 only). Indeed, a drive unit may be provisioned for each vacuum pump of a vacuum pump system. Whilst specific examples described herein show bus bars prescribing a particular path through a casing of a drive unit, this is not intended to be limiting. Within a drive unit, other paths for the bus bars are possible. Whilst specific examples described herein show bus bars all terminating at the same exterior side of a casing or a drive unit, different bus bars may instead terminate at different exterior sides of the casing. Whilst specific examples described herein may refer to maximum bend radius, maximum radius of curvature, maximum recommended radius of curvature, these will all be understood to be equivalent. Dimensions or sizing or shape shown and described for the examples herein are not intended to be limiting. Dimensions, sizing and shaping may be determined according to the application / system with which a drive unit assembly is associated or deployed. The drive unit assembly described herein includes busbars for power. The drive unit assembly described herein comprises busbars that extend to or beyond an exterior surface of a casing of the drive unit assembly. This tends to allow for cables / wires of a vacuum pump system to electrically connect to the bus bars at the exterior of the casing. This tends to allow cables / wires to electrically connect to the bus bars without needing to undergo sharp turns or bends. This tends to mitigate the risk of cables / wires of a vacuum pump system being bent beyond their maximum recommended radius of curvature. This tends to mitigate cables / wires or their connections breaking or undergoing excessive wear. The drive unit assembly described herein tends to mitigate increased servicing requirements and costs owing to cables / wires being installed at or beyond their manufactured tolerances (i.e., beyond their maximum recommended radius of curvature). The drive unit assembly described herein tends to allow for installation with vacuum pump systems wherein the drive unit assembly must be installed in a horizontal configuration. The drive unit assembly described herein tends to allow for more compact vacuum pump systems with reduced spatial footprint. The drive unit assembly described herein tends to decrease the area / volume required for the drive units cabling / wiring. The drive unit assembly described herein tends to retain the busbars securely using channels in a casing of the drive unit assembly. Reference numeral list 100 Vacuum pump system 110 First vacuum pump 120 Second vacuum pump 130 Drive unit assembly 140 System casing 150 Void 200 Drive unit assembly 210 First drive unit 211a First top cover 211a1 Channel 211b First middle cover 211b1 Edge 211b2 Channel 211 b3 Channel 211c First bottom cover 212 First circuit 213 One or more first busbars 213a First connections 214 One or more second busbars 214a Second connections 220 Second drive unit 221a Second top cover 221b Second middle cover 221 b1 Edge 221c Second bottom cover 222 Second circuit 223 One or more third busbars 223a Third connections 5 224 Interconnecting busbars 225 One or more fourth busbars 225a Fourth connections 300 Method 310 Providing step 10 320 Arranging step 330 Connecting step 340 Arranging step 350 Connecting step 15

Claims

1. A drive unit assembly for a vacuum pump system, the drive unit assembly comprising a first drive unit comprising:a first casing containing a first circuit for driving a first motor of a first vacuum pump, the first circuit having a first alternating current, AC, input and a first AC output;one or more first bus bars connected to the first AC input, the one or more first bus bars being arranged to extend outwardly of the first casing to or beyond an exterior side of the first casing for connecting to one or more first cables and / or wires of the vacuum pump system; andone or more second bus bars connected to the first AC output, the one or more second bus bars being arranged to extend outwardly of the first casing to or beyond the exterior side of the first casing for connecting to one or more second cables and / or wires of the vacuum pump system.

2. The drive unit assembly of claim 1, wherein:the one or more first bus bars extend linearly beyond the exterior side of the first casing; and / orthe one or more second bus bars extend linearly beyond the exterior side of the first casing.

3. The drive unit assembly of claim 1, wherein:the one or more first bus bars extend around an edge of the first casing and along the exterior side of the first casing; and / orthe one or more second bus bars extend around an edge of the first casing and along the exterior side of the first casing.

4. The drive unit assembly of any preceding claim, wherein:the one or more first bus bars comprise three bus bars; andthe one or more second bus bars comprise three bus bars.

5. The drive unit assembly of any preceding claim, wherein:the one or more first bus bars and the one or more second bus bars comprise copper.

6. The drive unit assembly of any preceding claim, wherein:the one or more first bus bars and the one or more second bus bars are substantially flat.

7. The drive unit assembly of any preceding claim, wherein:the one or more first bus bars comprise one or more first ring terminal connections exterior to the first casing for connecting to the one or more first cables and / or wires; and / orthe one or more second bus bars comprise one or more second ring terminal connections exterior to the first casing for connecting to the one or more second cables and / or wires.

8. The drive unit assembly of any preceding claim, wherein:the first casing comprises a first top cover, a first middle cover, and a first bottom cover;wherein the one or more first bus bars and one or more second bus bars are arranged between the first top cover and the first middle cover; andwherein the first circuit is arranged between the first middle cover and the first bottom cover.

9. The drive unit assembly of claim 8, wherein the first top cover and / or first middle cover comprise:one or more first channels for receiving respective first bus bars of the one or more first bus bars; andone or more second channels for receiving respective second bus bars of the one or more second bus bars.

10. The drive unit assembly of any one of claims 8-9, wherein:the first middle cover, the one or more first bus bars, and the one or more second bus bars comprise one or more collocated holes;wherein electrically conductive bolts are arranged through the collocated holes for electrically connecting the one or more first bus bars and one or more second bus bars to the first circuit.

11. The drive unit assembly of any preceding claim, wherein the first casing comprises plastic.

12. The drive unit assembly of any preceding claim, further comprising a second drive unit, the second drive unit comprising:a second casing containing a second circuit for driving a second motor of a second vacuum pump, the second circuit having a second AC input and a second AC output;one or more third bus bars connected to the second AC output, the one or more third bus bars extending outwardly of the second casing to or beyond an exterior side of the second casing for connecting to one or more third cables and / or wires of the vacuum pump system;wherein the drive unit assembly further comprises one or more interconnecting bus bars connected between the one or more first bus bars and the second AC input, such that the first AC input and the second AC input are electrically connected in parallel.

13. The drive unit assembly of claim 12, wherein:the second drive unit further comprises one or more fourth bus bars connected to the second AC output, the one or more fourth bus bars extending outwardly of the second casing to or beyond an exterior side of the second casing for connecting to one or more fourth cables and / or wires of the vacuum pump system.

14. A vacuum pump system comprising:one or more vacuum pumps; andthe drive unit assembly of any preceding claim.

15. A method of electrically connecting a drive unit assembly to a vacuum pump system, the method comprising:providing the drive unit assembly of any one of claims 1 -13;arranging one or more first cables and / or wires of the vacuum pump system to extend substantially parallel the exterior side of the first casing of the drive unit assembly;connecting the one or more first cables and / or wires to the one or more first bus bars at a position where the one or more first bus bars extend to or beyond the exterior side of the first casing;arranging one or more second cables and / or wires of the vacuum pump system to extend substantially parallel the exterior side of the first casing of the drive unit assembly; andconnecting the one or more second cables and / or wires to the one or more second bus bars at a position where the one or more second bus bars extend to or beyond the exterior side of the first casing.

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