Method and Apparatus for Monitoring Machine Tool Coolant

Abstract

An apparatus 101 for monitoring machine tool coolant is configured for locating within a machine tool coolant tank. The apparatus includes a sample chamber 107, and means (127, 109, 129, Figure 4) to

Description

Machine tools are used for handling, processing and / or machining rigid materials, typically metal, and typically in industrial processes. Examples of machine tools are CNC, lathe, drilling, milling, cutting, boring and grinding machines. A key component of a machine tool is the cooling system which uses a fluid or combination of fluids to cool the workpiece and the tool, and may also be used to flush or otherwise remove waste material such as cuttings, swarf and the like. The coolant fluid (which might also be referred to as a cutting fluid) also serves to prevent corrosion of the machine tool itself. Amongst other maintenance services, machine tool coolant condition monitoring is offered as a service (or part of a maintenance service) to monitor the condition of machine tool coolant. In the United Kingdom, the Control of Substances Hazardous to Health Regulations 2002 (COSHH) requires employers to prevent or at least control exposure to substances hazardous to health. This places obligations on employers to protect employees so that they are not made ill. Amongst those substances which can be harmful to health are metalworking fluids which can harbour bacteria and fungi which can give rise to dermatitis and asthma, and other skin and respiratory diseases. COSHH essentials for machining with metalworking fluids MW5 “Managing Fluid Quality”, issued by the Health and Safety Executive (HSE), describes good practice for managing fluid quality of metalworking fluids, and provides guidance to ensure compliance with the law. The Applicant is concerned that there are significant limitations in at least some aspects of the manner in which machine tool coolant condition is monitored, most notably the manner in which contamination by micro-organisms (bacteria and fungi) is determined. The traditional approach to determining the presence or level of contamination, and that which is set out in HSE Managing Fluid Quality MW5 discussed above, involves a highly subjective comparison of an incubated dipslide against a comparison chart (see example below). The procedure set out in MW5 requires the following notable points: • Stirring the sump (coolant tank) before testing; • Using a dipslide to check the metalworking fluid for bacteria; • Using a dipslide incubator to keep the temperature the same for each test; • Take dipslides once a week; • Measure fluid concentration and pH weekly; • Measure the sump temperature weekly; • Add biocide but only after other practice measures to maintain the fluid have been followed (concentration, pH, tramp oil content, metal contamination, operating temperature, agitation and flow). The initial act of stirring the tank can make certain pathogens airborne and increase the risk of exposure of contaminants to an employee or contractor tasked with this exercise. Use of a dipslide inevitably increases the risk of exposure as the coolant tank or sump must be opened and the dipslide inserted into the fluid and retrieved by the employee or contractor. The requirement for dipslide incubation also increases complexity and requires that dipslides be quickly stored in a temperature regulated environment, necessary to ensure repeatability and consistency. The requirement to take dipslides once a week is also quite onerous and increases operational costs. It is also the case that the machine would be shut down during the dipslide check resulting in lost productivity. Conversely, the requirement to only measure weekly (this applies also to concentration, pH and temperature checks) poses the risk that significant problems might occur and go undetected for sufficiently long periods of time that damage to equipment and harm to persons might happen. Anecdotally, the Applicant has found that dipslide checks are actually performed far less frequently than recommended by the guidelines, and rather than being taken directly from the tank (following stirring) they are often taken directly from coolant jets in the tooling or working area for ease of access. Unfortunately ease of access comes at obviously increased risk to an employee or contractor tasked with this exercise. The addition of biocide is only recommended after control is attempted by adjusting concentration, pH, tramp oil content, metal contamination, operating temperature, agitation and flow. However, if testing of each parameter is only done weekly (at most), and if dipslide incubation of several days is required, this can take a long time to resolve. If unsuccessful, or if contamination is heavy, then urgent and drastic measures should be taken, and these might include draining and cleaning the system completely. As these checks are time consuming they can occasionally be overlooked or otherwise missed in busy production environments. While it is possible to reduce the frequency of 1 such checks while remaining compliant with the guidelines, there would need to be a 2 prolonged history of compliance and effective quality management before this could be 3 considered. In addition to safeguarding employees, it would simply be preferable to 4 ensure compliance with the law rather than risk sanctions by health and safety inspectors. 5 6 It is therefore an object of at least one aspect of the present invention to obviate and / or 7 mitigate one or more disadvantages of known / prior approaches to monitoring machine tool 8 coolant such as described above. 9 10 Further aims and objects of the invention will become apparent from reading the following 11 description. 22 12 25 Summary of the invention According to a first aspect of the invention, there is provided a method of monitoring machine tool coolant for contamination by micro-organisms, the method comprising locating a sampling apparatus within a machine tool coolant tank, obtaining a sample of machine tool coolant in situ, measuring an oxygen uptake rate within the sample, and determining whether the machine tool coolant is contaminated by micro-organisms based on the measured oxygen uptake rate, or a change in the measured oxygen uptake rate, exceeding a threshold or predetermined value. Preferably, the oxygen uptake rate is measured by closed cell respirometry. Preferably, the sample is held in a sealed sample chamber within the sampling apparatus and measuring dissolved oxygen as a function of time. Optionally, the method comprises determining to what extent the machine tool coolant is contaminated by micro-organisms. Most preferably, the method is performed without powering down the machine tool. Preferably, the method further comprises performing one or more actions responsive to a determination that the machine tool coolant is contaminated by a micro-organism. The method may comprise dosing the machine tool coolant with an inoculant or a biocide. Alternatively, or additionally, the method may comprise shutting down or disabling the machine tool. Optionally, the method further comprises determining whether the machine tool coolant is otherwise non-compliant. Preferably, the method further comprises performing one or more actions responsive to a determination that the machine tool coolant is otherwise non-compliant. Optionally, the method comprises measuring the refractive index of the sample. The refractive index may be used to determine machine tool coolant concentration. Optionally, the method may comprise adding coolant concentrate to the machine tool coolant tank or diluting the coolant within the machine tool coolant tank responsive to the determined machine tool coolant concentration. Optionally, the method comprises measuring the temperature of the sample. Optionally, the method comprises measuring the pH of the sample. The temperature and / or the pH of the sample may be used to determine coolant condition and the pH of the sample may be used as another indicator of bacterial growth. Optionally, determining whether the machine tool coolant is contaminated by microorganisms is also based on the pH of the sample. The method may be performed continuously. Alternatively, the method may be performed periodically, optionally according to a maintenance schedule and / or during machine tool downtime. The method may comprise agitating the machine tool coolant within the machine tool coolant tank prior to obtaining a sample of the machine tool coolant. The method may comprise drawing a sample into the sample chamber. The method may comprise ejecting a sample from the sample chamber after the oxygen uptake rate has been measured. According to a second aspect of the invention, there is provided a machine tool coolant monitoring apparatus, the apparatus configured for locating within a machine tool coolant tank and comprising a sample chamber, means to obtain a sample of machine tool coolant from the machine tool coolant tank into the sample chamber, means for measuring an oxygen uptake rate within the sample chamber, and means for determining whether the machine tool coolant is contaminated by micro-organisms based on the measured oxygen uptake rate, or a change in the measured oxygen uptake rate, exceeding a threshold or predetermined value. Preferably, the means to obtain a sample comprises one or more inlets to the sample chamber and one or more outlets from the sample chamber, and a gate moveable within the sample chamber between the one or more inlets and the one or more outlets to draw a sample of machine tool coolant into the sample chamber. Optionally, the apparatus further comprises one or more magnets located proximate to the one or more inlets. Optionally, the apparatus further comprises one or more magnets located proximate to the one or more outlets. Optionally, the apparatus further comprises a screen or filter located over the one or more inlets. Optionally, the apparatus further comprises a screen or filter located over the one or more outlets. Preferably, the apparatus comprises sealing means to seal the sample chamber while the oxygen uptake rate is measured. Preferably, the means for measuring the oxygen uptake rate comprises a dissolved oxygen sensor in communication with the sample chamber. Optionally, the apparatus further comprises a temperature sensor. Optionally, the apparatus further comprises a pH sensor. Optionally, the apparatus further comprises a refractive index sensor. Preferably, a cross-section of the sample chamber forms a sector of a circle with a pivot axis of the gate at its centre. Preferably, the sector has a central angle of 90 degrees. Preferably, an end of the gate opposite the pivot axis sweeps out an arc corresponding to the arc of the sector of the cross-section of the sample chamber. Preferably, the apparatus comprises means to submerge the apparatus in the machine tool coolant. Optionally, the submerging means may comprise one or more weights. Alternatively, the apparatus may comprise means to attach the apparatus within the machine tool coolant tank. Optionally, the attachment means may include one or more magnets. Alternatively, the apparatus may be integrated in the machine tool coolant tank. Embodiments of the second aspect of the invention may comprise features corresponding to the preferred or optional features of the first aspect of the invention or vice versa. In particular, the method of the second aspect may include steps corresponding to features of the apparatus of the first aspect, and vice versa. There can also be provided a method of monitoring a fluid for contamination by one or more micro-organisms, the method comprising locating a sampling apparatus within the fluid, obtaining a sample of the fluid in situ, measuring an oxygen uptake rate within the sample, and determining whether the fluid is contaminated by micro-organisms based on the measured oxygen uptake rate. The method of monitoring a fluid for contamination by one or more micro-organisms may comprise features corresponding to the preferred or optional features of the first or second aspects of the invention. In particular, the method may comprise any of the preferred or optional features of the first aspect, the necessary changes having been made. There can also be provided an apparatus for monitoring a fluid for contamination, the apparatus configured for locating within a fluid and comprising a sample chamber, means to obtain a sample of fluid into the sample chamber, and means for measuring an oxygen uptake rate within the sample chamber. The apparatus for monitoring a fluid for contamination may comprise features corresponding to the preferred or optional features of the first or second aspects of the invention. In particular, the apparatus may comprise any of the preferred or optional features of the second aspect, the necessary changes having been made. It is envisaged that the apparatus need not be located within the coolant tank (or within the fluid as the case may be), and simply rely on the Applicant’s realisation that determining oxygen uptake rate is significantly more effective than prior art approaches. As such there can also be provided a method of monitoring machine tool coolant or another fluid, the method comprising obtaining a sample of the machine tool coolant or the fluid, measuring an oxygen uptake rate within the sample, and determining whether the machine tool coolant or the fluid is contaminated by micro-organisms based on the measured oxygen uptake rate. Likewise there can also be provided an apparatus for monitoring machine tool coolant or another fluid, the apparatus comprising a sample chamber and means to obtain a sample of the machine tool coolant or the fluid into the sample chamber, and means for measuring an oxygen uptake rate within the sample chamber to determine whether the machine tool coolant or the fluid is contaminated by micro-organisms. The method and apparatus may likewise comprise features or steps corresponding to features or steps of any of the first and second aspects, the necessary changes having been made. 22 12 25 1 Brief description of the drawings 2 3 There will now be described, by way of example only, embodiments of aspects of the 4 invention with reference to the drawings (like reference numerals being used to denote like 5 features), of which: 6 7 Figure 1 is a front perspective view of a machine tool coolant monitoring apparatus 8 according to an embodiment of the present invention; 9 10 Figure 2 is a rear perspective view of the machine tool coolant monitoring apparatus of 11 Figure 1; 12 13 Figure 3 is a top-down perspective view showing the interface between a sample chamber 14 and an instrument chamber of the machine tool coolant monitoring apparatus of Figure 1; 15 16 Figures 4 to 6 illustrate the operation of the sample chamber of the machine tool coolant 17 monitoring apparatus of Figure 1 to collect a fluid sample from a body of fluid in which the 18 apparatus is submerged; 19 20 Figure 7 is a graph showing an objective comparison between a method of determining 21 contamination according to an embodiment of the present invention and the state of the art 22 approach. LO CXI CXI i— CXI CXI 1 Detailed description of preferred embodiments 2 3 As explained in the Background above, contamination of coolant by micro-organisms is 4 traditionally and conventionally determined by comparing an incubated dip slide against a 5 comparison chart. This method is highly subjective and while the Applicant has 6 considered automating this process to an extent, for example using image analysis, 7 pattern recognition, machine learning (and combination thereof) it still relies on an 8 unreliable technology. Even training data, which might be used to develop an automated, 9 machine-learning based method of interpreting dip-slide measurements, would likely be 10 based on human interpretation. 11 12 Faced with this problem, the Applicant had the realisation that measuring and monitoring 13 of oxygen uptake rate in a machine tool coolant sample may provide a more robust, 14 repeatable and reliable means of determining whether machine tool coolant was 15 contaminated by micro-organisms. Following a laboratory comparison of this novel 16 approach versus the traditional and conventional incubated dip slide approach, this was 17 confirmed and as explained below the Applicant made the surprising discovery that it is in 18 fact a more reliable means of determining whether machine tool coolant was contaminated 19 by micro-organisms, not simply because the subjectivity of the earlier approach was 20 avoided, but because it detects contamination which the earlier approach would not. 21 22 Note that MW5 as described in the Background states that it is important to follow all the 23 points set out in the guidelines, it is also permitted to “use equally effective measures”. 24 The following sets out how and why the inventive concept exceeds the HSE requirements 25 and can therefore be described as far more effective measures than those set out in the 26 guidelines. 27 28 Sampling Apparatus 29 30 Shown in Figures 1 and 2 are front and rear perspective views of a machine tool coolant 31 monitoring apparatus 101 in accordance with an aspect of the invention. The machine tool 32 coolant monitoring apparatus 101 (CMA for short) comprises a housing 103 which in this 33 embodiment comprises a lidded instrument chamber 105 and a lidded sample chamber 34 107. The instrument chamber 105 is a substantially rectangular enclosure which houses 35 the various instruments, electronics and motor which perform measurements on the sample within the sample chamber 107 and control the collection and ejection of samples to and from the sample chamber 107. The instrument chamber 105 is preferably sealed but this can be dispensed with if the instruments within are potted or alternatively waterproofed. The sample chamber 107 (operation and internal features of which are described further below) abuts the instrument chamber 105 and has a cross-section shape of a 90 degree sector of a circle, and within the sample chamber is located a gate 109 which has a pivot axis 111 about the centre of said circle and which extends to an interior wall 113 of the sample chamber 107 so as to sweep out an arc corresponding to the shape of the sample chamber 107 when rotated about the pivot axis 111. The gate 109 is linked through the lid 115 of the sample chamber to a gear 117 which is driven by a motor (not shown) within the instrument chamber 105 via drive gears 119 and 121. Gear 123 is also driven by the drive hears 119 and 121 simultaneously, and is linked through the lid 115 of the sample chamber to a column valve 125 which serves to open and close the sample chamber inlet 127 as visible in Figure 1. Visible in Figure 2 is the sample chamber outlet 129 which is closed by the rear face 109B of the gate 109. In this position, with the inlet 127 and the outlet 129 closed, the sample chamber 107 provides a closed volume for the purposes of closed cell respirometry to measure dissolved oxygen within the sample chamber 107 as a function of time and thereby determine an oxygen uptake rate (OUR) within the sample chamber 107. As noted above, the Applicant realised and confirmed by experimentation (see below) that OUR is a far more reliable and robust method of detecting contamination within a machine tool coolant. Figure 3 is a top-down perspective view showing the interface between the sample chamber 107 and the instrument chamber 105. In this embodiment the sample chamber 107 and the instrument chamber 105 are components of the housing 103 which are joined together to form the apparatus 101, but it is envisaged that a sample chamber and an instrument chamber could be integrally formed in a one-piece housing. In this embodiment, the respective side wall of the sample chamber 107 comprises an aperture which allows instruments located in instrument apertures 131, 133 and 135 to interrogate or otherwise perform measurements on a fluid contained within the sample chamber 107. In this embodiment, the instruments are a pH sensor, a refractive index sensor, and a dissolved oxygen probe. Shown in Figures 4, 5 and 6 are three stages during the action of drawing a sample into the sample chamber 107 (a) from a first position observing the sample chamber inlet 127 and (b) from a second position observing the sample chamber outlet 129. Note that the lid 115 that would otherwise enclose the sample chamber 107 at the top has been removed to show the inside of the sample chamber 107 during this process. As shown in Figure 4, the inlet 127 and the outlet 129 are both open and, assuming the apparatus is submerged in machine tool coolant within a machine tool coolant tank, machine tool coolant is able to flow into and out of the sample chamber 107. In this position, the gate 109 is positioned against the sidewall of the sample chamber 107 which is open to the instrument apertures 131, 133 and 135. As such the instruments are covered and thereby protected. Indeed, it is envisaged that when inserting the apparatus 101 in a machine tool coolant tank the gate 109 be in this position for that very reason, As described above the gate 109 is rotated via gear 117 and as shown at around the midway point in Figure 5 the movement of the gate 109 draws fluid into the sample chamber 107 via the inlet 127. Note that there are located sets of magnets 137 and 139 at the inlet 127 and the outlet 129 respectively; these are to collect swarf and / or other metallic materials which might otherwise enter the sample chamber 107 and cause damage, or block the gate from operating correctly. There can also be provided a mesh or filter (not shown) over the inlet 127 and 129 to trap other materials which would not be collected by said magnets 137 and 139, though the mesh size should be large enough to allow bacteria, fungi and other microorganisms to pass through. It should be observed that the gear 123 is driven simultaneously with gear 117 such that as the gate 109 sweeps around the sample chamber 107, drawing fluid into the chamber 107 in front of the gate 109 while ejecting fluid from the chamber 107 behind the gate 109, the column valve 125 gradually closes the inlet. When the gate 109 has completed its sweep as shown in Figure 6 it abuts the rear wall of the sample chamber 107. A rectangular protrusion on the rear face 109B of the gate 109 is shaped to be received in the outlet 129 hence closing it and effecting a sufficient seal. In this position the column valve 125 is also completely closed, effecting a sufficient seal of the inlet 127. At this point, the instruments located in the instrument apertures 131, 133 and 135 (see Figure 3) begin to interrogate or otherwise perform measurements on the fluid now contained and effectively (or sufficiently) sealed within the sample chamber 107. The pH and refractive index measurements are relatively standard and do not necessarily need to be performed on a sealed sample, although this gives the sampled fluid time to settle prior to measurements being taken. (Note that pH can be a secondary or alternative means of determining bacterial growth though it is also unreliable and in the state of the art cannot be used to replace dipslides; anecdotally badly infected machines have been known to exhibit “good” pH readings). Housing the sensors within the sample chamber will also reduce the possibility of potentially damaging contact between contaminants (such as swarf and other debris) and the sensors, particularly if magnets and / or mesh (and the like) are used to prevent same from entering the sample chamber. Reversing this process once the necessary measurements have been taken will eject the sample through the inlet 127 (in effect temporarily an outlet) and repeating it will draw a new sample into the sample chamber 107 through the inlet 127. This can be repeated continuously to provide a near real-time monitoring of machine tool coolant condition but in practice it may be preferable to run the process, say, once a day to maximise battery life (if remote power is not available) and reduce wear and tear on the components of the apparatus. Even a daily schedule of this nature will significantly increase the quality, accuracy and consistency of the fluid monitoring over conventional approaches which, at best, are typically carried out weekly (often less frequently) with days to wait for results. The skilled person will realise that other shapes and configurations of apparatus and / or sample chamber may be employed without departing from the scope of the invention which is defined by the appended claims. For example, the sample chamber may be substantially cylindrical and have a gate which rotates about a central axis of the cylindrical sample chamber, with the instrument chamber located above, below or centrally within the sample chamber (or alternatively within the gate). Alternatively the sample chamber may be generally square or rectangular in cross-section, with a gate which travels linearly within the sample chamber to collect and eject samples. Such a gate might run on rails or the like in the walls and / or floor and ceiling of the sample chamber. When locating the apparatus within a machine tool coolant tank it will be advantageous to ensure it is submerged in the coolant fluid and that it is held in place. This can be done by weighting the apparatus (to hold it under the surface of the fluid) and / or by using magnets to hold the apparatus against the typically metal walls of the machine tool coolant tank. Equivalent means may be employed, such as adhesives or even more permanent attachments such as bolts or rivets. Alternatively it is foreseen that the apparatus could be integrally formed with the machine tool coolant tank. It is also envisaged that the sample chamber and indeed the entire apparatus might be located outside of the machine coolant tank (or other reservoir) with machine tool coolant (or other fluid) instead pumped in or otherwise delivered to the sample chamber via one or more conduits and pumped out of or otherwise ejected from the sample chamber via the same or other one or more conduits. As noted above, the most important feature of the invention and its embodiments is that the OUR is measured. It is preferable that the apparatus comprise a display, and it is envisaged that the display would show the measured parameters, for example DO / OUR, pH, temperature and / or refractive index. Alternatively, or additionally, the display may show derived parameters or qualities such as low / medium / high degrees of contamination (perhaps using a traffic light approach of green / amber / red respectively) and coolant concentration. The display might prompt a user to make an intervention, for example dosing the machine tool coolant with an inoculant or biocide if contamination is determined, cooling or heating the machine tool coolant if it is determined to be outside desired operating temperatures, or adding coolant concentrate or diluent if the concentration is determined to be outside desired operating levels. Alternatively, it is envisaged that such interventions may be performed automatically responsive to such determinations. As noted above, HSE guidelines prioritise environmental adjustments over chemical interventions, with biocides and the like added as a last resort if other attempts have failed. To enable automatic adjustment of other parameters, such as concentration, pH, operating temperature etc. the apparatus might be provided with various means for controlling these parameters. For example, micro pumps to add coolant concentrate, inoculants or biocides, or even oxygen, and heaters / coolers to control the temperature of the coolant. Alternatively these means may be provided separately (or be embodied within the machine tools already, one way or another) and simply controlled by the apparatus. The measured data might be measured and displayed in real time, periodically, or continuously show the most recent measured or derived parameters or qualities for ease of use. The data can be stored locally and / or transmitted to a server which might receive LO CXI CXI i— CXI CXI 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 data from a plurality of machine tool coolant monitoring apparatus in a plurality of machine tool coolant tanks. Comparison of Test Data Shown in Figure 7 is a graph comparing measurements obtained using the conventional, HSE-approved, dipslide approach and the approach used in the present invention, whereby oxygen uptake rate (OUR) is determined by closed cell respirometry within a sample chamber of an apparatus such as described above. The Y axis shows, in colony forming units per agar, the level of contamination for a number of samples tested using the dip slide approach, against the X axis which shows, in mg / L / h, the corresponding oxygen uptake rate (OUR) determined using closed cell respirometry. In other words, each data point on the graph represents a particular sample and indicates the result of both test types for said sample. There are shown three boxed areas labelled A, B, C which are intended to represent “safe”, “concerning” and “dangerous” coolant conditions. Although somewhat arbitrary, this is intended to represent where a machine tool might continue operating because the coolant condition was found to be “safe”, where an intervention might be recommended and / or undertaken because the coolant condition was found to be “concerning”, and where machine shutdown, coolant removal and tank cleaning might be necessary to respond to a coolant deemed to be in “dangerous” condition. For the avoidance of doubt these measures relate only to the level of contamination by micro-organisms and not other parameters such as pH, temperature or concentration. It is foreseen that pH, temperature and / or concentration might also prompt an intervention. These boxes may define thresholds (or predetermined values) at which contamination or degrees of contamination are determined. Specific thresholds (or predetermined values) may be set and / or varied according to HSE guidelines, minimum operating parameters of machine tools, combinations thereof or indeed any other criteria. It is at least envisaged that there will be a certain OUR value (though it may be temperature and / or composition dependent) at which the methods and apparatuses disclosed herein will determine there to be contamination. It is also foreseen LO CXI CXI i— CXI CXI 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 that contamination might be determined based on a measured change in OUR value (for example from a base level reading which might be non-zero). Note that the HSE guidance considers dipslide results showing heavy contamination with bacteria at or above 106 CFU / ml to indicate poor control which requires immediate action; “This normally means draining and cleaning the system or taking other measures which are equally effective”. 106 CFU / ml roughly corresponds to 500 CFU / agar and therefore corresponds to the “dangerous” coolant conditions in region C of Figure 7. The smallest boxed area A (dotted outline) shows the “safe” region with generally good correlation between the dipslide and OUR measurements, although it is already clear that the OUR method detects the presence of contaminants where the dipslide measurements indicate low or no CFUs. The next region B (short-dashed outline) indicates the “concerning” region in which there is mostly reasonable correlation between the dipslide and OUR measurements but already some instances where the observed number of CFUs are at or near zero but the OUR indicates significant contamination. The next and final region C (long-dashed outline) indicates a “dangerous” region in which contamination is sufficiently high to warrant urgent intervention, but there are several more concerning instances where the number of CFUs are at or near zero but the OUR indicates very significant contamination. The region indicated in general by triangle D highlights situations where the dipslide technique effectively misses a significant number of contaminations which the Applicant would identify as qualifying for immediate action according to HSE guidelines. It should be noted that there are no instances where the opposite is true; no instances where OUR indicates no or low contamination where the dipslide measurement indicated otherwise. This test alone justifies the Applicant’s confidence that OUR monitoring provides a far more reliable and robust indicator of contamination of machine tool coolant with micro-organisms than the conventional, HSE-approved dipslide method. It should also be noted that checking of dipslides is typically performed by manual inspection, with an incubated dipslide compared visually and therefore subjectively with a sample or test card with indicative CFU values. For the purposes of a fair comparison (i.e. based on the best possible interpretation of the dipslide data) in the exercise above the number of CFUs were determined in each case by image analysis. As such it is to be expected that in reality the accuracy and reliability of the dipslide approach will be poorer. The Applicant realises that the underpinning inventive concept, that is using oxygen uptake rate as an indicator of contamination of machine tool coolant by microorganisms, can be applied to other fluids. For example, it is envisaged that this approach can be used in the fields of healthcare, hospitality, and food and drink, to monitor fluids for bacterial and fungal contamination (or indeed any contamination which might be indicated by respiration). For example, in hospitals and other healthcare settings, this approach can be used to monitor water supplies for bacterial and fungal contamination, and it is envisaged that apparatus such as described above may be located in water tanks which supply various amenities (drinking water and equipment supply). In food and drink production this approach can be used to monitor not only water but other liquids such as alcohol, and used within the liquid process of sugar for example. The apparatus and methods described above can therefore be applied in other fields, the necessary changes having been made (for example hermetically sealing the apparatus for use in drinking water supplies and enlargement of apertures etc. to accommodate more viscous fluids). The invention provides a more robust, repeatable and reliable method of monitoring machine tool coolant for contamination by micro-organisms such as bacteria and fungi than possible using state of the art techniques. Rather than employing dipslides as stipulated in legislation, the invention monitors dissolved oxygen in a coolant sample to determine an oxygen uptake rate which can reveal the presence of micro-organisms in the sample. It has been found that the invention identifies the presence of micro-organisms where conventional methods did not, meaning that contamination that might otherwise be missed can be caught. Following detection of contamination, a number of interventions may occur in response, such as dosing the machine tool coolant with a biocide or an inoculant. The invention also provides an apparatus for obtaining a sample and making such a measurement of oxygen uptake rate, which has a sample chamber which can obtain a sample and thereafter be sealed to allow closed cell respirometry to take place. As may be used herein, the terms bottom, lower, below and the like are descriptive of a feature that is located towards a first end / side of an apparatus, system or component while the terms top, upper, above and the like are descriptive of a feature that is located towards a second, opposing end / side of the apparatus, system or component. Such an apparatus, system or component may be inverted without altering the scope of protection which, as below, is defined by the appended claims. Throughout the specification, unless the context demands otherwise, the terms “comprise” or “include”, or variations such as “comprises” or “comprising”, “includes” or “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of monitoring machine tool coolant for contamination by microorganisms, the method comprising locating a sampling apparatus within a machine tool coolant tank, obtaining a sample of machine tool coolant in situ, measuring an oxygen uptake rate within the sample, and determining whether the machine tool coolant is contaminated by micro-organisms based on the measured oxygen uptake rate, or a change in the measured oxygen uptake rate, exceeding a threshold or predetermined value.

2. The method of claim 1, wherein the oxygen uptake rate is measured by closed cell respirometry.

3. The method of claim 2, wherein the sample is held in a sealed sample chamber within the sampling apparatus and measuring dissolved oxygen as a function of time.

4. The method of any preceding claim, comprising determining to what extent the machine tool coolant is contaminated by micro-organisms.

5. The method of any preceding claim, wherein the method is performed without powering down the machine tool.

6. The method of any preceding claim, wherein the method further comprises performing one or more actions responsive to a determination that the machine tool coolant is contaminated by a micro-organism.

7. The method of any preceding claim, wherein the method comprises dosing the machine tool coolant with an inoculant or a biocide, and / or shutting down or disabling the machine tool.

8. The method of any preceding claim, wherein the method further comprises determining whether the machine tool coolant is otherwise non-compliant.

9. The method of claim 8, wherein the method further comprises performing one or more actions responsive to a determination that the machine tool coolant is otherwise non-compliant.

10. The method of any preceding claim, wherein the method comprises measuring the refractive index, temperature and / or pH of the sample.

11. The method of claim 10, wherein determining whether the machine tool coolant is contaminated by micro-organisms is also based on the pH of the sample.

12. The method of any preceding claim, wherein the method comprises agitating the machine tool coolant within the machine tool coolant tank prior to obtaining a sample of the machine tool coolant.

13. The method of any preceding claim, wherein the method comprises drawing a sample into the sample chamber prior to measuring the oxygen uptake rate and ejecting the sample from the sample chamber after the oxygen uptake rate has been measured.

14. A machine tool coolant monitoring apparatus, the apparatus configured for locating within a machine tool coolant tank and comprising a sample chamber, means to obtain a sample of machine tool coolant from the machine tool coolant tank into the sample chamber, means for measuring an oxygen uptake rate within the sample chamber, and means for determining whether the machine tool coolant is contaminated by micro-organisms based on the measured oxygen uptake rate, ora change in the measured oxygen uptake rate, exceeding a threshold or predetermined value.

15. The apparatus of claim 14, wherein the means to obtain a sample comprises one or more inlets to the sample chamber and one or more outlets from the sample chamber, and a gate moveable within the sample chamber between the one or more inlets and the one or more outlets to draw a sample of machine tool coolant into the sample chamber.

16. The apparatus of claim 14 or claim 15, wherein the apparatus further comprises one or more magnets located proximate to the one or more inlets and / or the one or more outlets.

17. The apparatus of any of claims 14 to 16, wherein the apparatus further comprises a screen or filter located over the one or more inlets and / or the one or more outlets.

18. The apparatus of any of claims 14 to 17, wherein the apparatus comprises sealing means, which may comprise a column valve, to seal the sample chamber while the oxygen uptake rate is measured.

19. The apparatus of any of claims 14 to 18, wherein the means for measuring the oxygen uptake rate comprises a dissolved oxygen sensor in communication with the sample chamber.

20. The apparatus of any of claims 14 to 19, wherein the apparatus further comprises a temperature sensor, a pH sensor, and / or a refractive index sensor.

21. The apparatus of any of claims 14 to 20, wherein a cross-section of the sample chamber forms a 90 degree sector of a circle with a pivot axis of the gate at its centre, and wherein an end of the gate opposite the pivot axis sweeps out an arc corresponding to the arc of the sector of the cross-section of the sample chamber.

22. The apparatus of any of claims 14 to 21, wherein the apparatus comprises one or more weights to submerge the apparatus in the machine tool coolant.

23. The apparatus of any of claims 14 to 21, wherein the apparatus comprises one or more magnets to attach the apparatus within the machine tool coolant tank.

24. The apparatus of any of claims 14 to 21, wherein the apparatus is integrated in the machine tool coolant tank.

Images