Method and system for ultrasonically determining homogeneity of material mixture in a volume

Abstract

There is disclosed a method of determining homogeneity of a material mixture in a volume. The method comprises receiving a first signal, from a first acoustic transducer at a first spatial position of the volume, indicative of an acoustic wave transmitted through the material mixture at the first spatial position of the volume. The method further comprises receiving a second signal, from a second acoustic transducer at a second spatial position of the volume, indicative of an acoustic wave transmitted through the material mixture at the second spatial position of the volume. The method further comprises comparing the first and second signals to determine the homogeneity of the material mixture within the volume.

Description

[0001] METHOD AND SYSTEM FOR ULTRASONICALLY DETERMINING HOMOGENEITY OF MATERIAL MIXTURE IN A VOLUME

[0002] The present disclosure relates to determining the homogeneity of a material mixture.

[0003] Homogeneity is the degree to which a mixture is uniform throughout, meaning that there are no visible or measurable differences between different parts of the mixture. The homogeneity of a material mixture is important in some manufacturing processes because, if the mixture is insufficiently homogeneous (in other words, if the mixture is heterogeneous), the quality of the product produced by the process may be inadequate.

[0004] Several techniques for determining the homogeneity of a material mixture are known. For example, a mixture can be visually inspected to identify any visible differences, such as colour variations, particle size differences, or layering. Visual inspection is inaccurate, and cannot be used to determine the homogeneity of internal regions of the mixture that are not visible.

[0005] As another example, samples can be taken from different parts of a material mixture and analysed for the presence of different components or impurities. Analytical techniques such as chromatography, spectrophotometry, or microscopy can be used to detect and quantify the presence of different materials within the mixture. Such sample-and-analysis techniques are slow, and cannot provide real-time information on the homogeneity of the mixture.

[0006] Other techniques for determining homogeneity include measurement of the rheological properties, dielectric constant or impedance of a material mixture. These techniques typically involve placing a probe in contact with the mixture and, therefore, require the probe to be cleaned to ensure accuracy.

[0007] Summary

[0008] The present disclosure relates to an improved way of determining the homogeneity of a material mixture using acoustic (e.g., ultrasonic) waves. In accordance with a first aspect, a method of determining homogeneity of a material mixture in a volume is provided. The method may comprise receiving a first signal, from a first acoustic transducer at a first spatial position of the volume, indicative of an acoustic wave transmitted through the material mixture at the first spatial position of the volume. The method may further comprise receiving a second signal, from a second acoustic transducer at a second spatial position of the volume, indicative of an acoustic wave transmitted through the material mixture at the second spatial position of the volume. The method may further comprise comparing the first and second signals to determine the homogeneity of the material mixture within the volume.

[0009] Comparing the first and second signals allows the homogeneity of the material mixture across, or throughout, the volume to be determined. When the first and second signals are substantially the same, the material mixture has substantially the same acoustic properties at the first and second spatial positions. It can thus be inferred that the material mixture is homogeneous. On the other hand, when the first and second signals are significantly different, the material mixture has different acoustic properties at the first and second spatial positions. It can thus be inferred that the material mixture is heterogeneous.

[0010] The method of determining homogeneity disclosed herein has several advantages over known techniques. First, the disclosed method can be performed in situ in real time (unlike sampling-and-analysis techniques). Second, the disclosed method can be performed non-invasively, e.g., without placing a probe in contact with the mixture (unlike techniques involving the measurement of rheological properties, dielectric constant or impedance). This, in turn, avoids or simplifies cleaning, reduces the risk of contamination, and reduces the risk of the material mixture leaking. Third, the disclosed method can be performed by retrofitting acoustic sensors to existing manufacturing equipment, without the need to modify the equipment significantly and without the need to change the manufacturing process performed by the manufacturing equipment.

[0011] The method disclosed herein can be used in a variety of manufacturing processes to help ensure that a material mixture used in, or produced by, the process is homogeneous. This can improve the quality of products produced by the manufacturing process. The disclosed method finds application in mix, meter and dispense (MMD) composite manufacture, although many other uses of the method are described herein.

[0012] The material mixture may be a polymer material mixture. The material mixture may be a composite material mixture.

[0013] The volume may be one or more of: a mixing chamber; a conduit; and a mould.

[0014] The acoustic transducers may be ultrasonic transducers. The acoustic transducers may operate above the upper audible limit of human hearing, typically above 20 KHz. For example, the acoustic transducers may operate in a frequency range of between around 20 kHz and around 20 GHz. The acoustic waves may be ultrasonic waves, which may be in the frequency range of between around 20 kHz and around 20 GHz.

[0015] The method may further comprise causing acoustic transducers to emit acoustic waves into the volume. For example, when the first and second acoustic transducers operate in pulse-echo mode, the method may comprise causing the first and second acoustic transducers to emit acoustic waves into the volume. Alternatively, when the first and second acoustic transducers operate in pitch-catch mode, the method may comprise causing third and fourth acoustic transducers to emit acoustic waves into the volume.

[0016] Comparing the first and second signals may comprise using a statistical analysis. The statistical analysis may comprise one or more of: a coefficient of variation comparison analysis; a correlation analysis; a cluster analysis; and a principal component analysis.

[0017] The method may further comprise determining whether the homogeneity of the material mixture falls within an acceptable homogeneity threshold. The method may further comprise continuing a mixing process of the material mixture if the homogeneity of the material mixture falls outside of the acceptable homogeneity threshold. Alternatively or additionally, the method may further comprise dispensing the material mixture if the homogeneity of the material mixture falls within the acceptable homogeneity threshold. Dispensing the material mixture may be preceded by halting the mixing process. In accordance with a further aspect, there is provided a computer program comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out any of the methods disclosed herein.

[0018] In accordance with a further aspect, there is provided a computer-readable medium comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out any of the methods disclosed herein.

[0019] In accordance with a further aspect, there is provided a system for determining homogeneity of a material mixture in a volume. The system may comprise a volume for receiving the material mixture. The system may comprise a first acoustic transducer positioned adjacent the volume at a first spatial position. The first acoustic transducer may be configured to produce a first signal indicative of an acoustic wave transmitted through the material mixture and received at the first acoustic transducer. The system may further comprise a second acoustic transducer positioned adjacent the volume at a second spatial position. The second acoustic transducer may be configured to produce a second signal indicative of an acoustic wave transmitted through the material mixture and received at the second acoustic transducer. The system may further comprise a processor configured to receive the first and second signals from the first and second acoustic transducers, respectively. The processor may be further configured to compare the first and second signals to determine the homogeneity of the material mixture within the volume.

[0020] The first and / or second acoustic transducers may be fixedly coupled to the volume. For example, the first and / or second acoustic transducers may be fixedly coupled to the volume by one or more of a gel or oil-based couplant. The couplant may be an adhesive.

[0021] Alternatively, the first and / or second acoustic transducers may be removably coupled to the volume. For example, the first and / or second acoustic transducers may be removably coupled to the volume by one or more of a magnetic fixture, a suction fixture, or a fastener fixture.

[0022] The system may further comprise an array of acoustic transducers, the array of acoustic transducers comprising the first and second acoustic transducers. Each of the acoustic transducers in the array may be positioned adjacent the volume at a different spatial position of the volume. Each of the acoustic transducers in the array may be configured to produce a signal indicative of an acoustic wave transmitted through the material mixture at the respective spatial position of the volume. Alternatively or in addition, each of the acoustic transducers in the array may be configured to emit an acoustic wave into the volume (and, hence, into the material mixture).

[0023] The processor may be further configured to receive the signal from each acoustic transducer of the array of acoustic transducers. The processor may be further configured to compare the signals to determine the homogeneity of the material mixture within the volume.

[0024] The processor may be further configured to cause the first and second acoustic transducers to emit acoustic waves into the volume.

[0025] The volume may comprise one or more of: a mixing chamber; a conduit; and a mould. The conduit may be disposed between, and in series with, a mixing chamber and a mould.

[0026] When the volume comprises the conduit, the first and second acoustic transducers may be located at different points along a length of the conduit. Alternatively, the first and second acoustic transducers may be located at substantially the same point along the length of the conduit, and the first acoustic transducer may have a different orientation with respect to the second acoustic transducer.

[0027] The processor may be located remotely from the first and second acoustic transducers and the volume.

[0028] The processor may be configured to communicate with the first and second acoustic processors via a communication network. The network may be a local area network (LAN) or a wide area network (WAN). The WAN may use the internet. In one particular implementation, the processor may be a cloud-based processor.

[0029] Alternatively, the processor may be a local processor. In other words, the processor may be co-located with the first and second acoustic transducers and the volume. In this example, the processor may be directly connected to the first and second acoustic transducers, e.g., by electrical cables or wires, without using a communication network.

[0030] In the system described above, the volume is part of the system. For example, the volume may be supplied together with the first and second acoustic transducers, which may already be pre-attached to the volume.

[0031] In accordance with another aspect, the first and second acoustic transducers may be supplied as a kit of parts, which can be retrofitted to an existing volume to allow the homogeneity of a material mixture to be determined.

[0032] Thus, a kit of parts for determining the homogeneity of a material mixture in a volume may be provided, the kit of parts comprising a first acoustic transducer configured to emit a first signal indicative of an acoustic wave transmitted through the material mixture at a first spatial position of the volume. The kit of parts may further comprise a second acoustic transducer configured to emit a second signal indicative of an acoustic wave transmitted through the material mixture at a second spatial position of the volume. The kit of parts may further comprise a processor connectable to the first and second acoustic transducers. The processor may be configured to receive the first and second signals, and compare the first and second signals to determine the homogeneity of the material mixture within the volume. The kit of parts may optionally further comprise any of the features of any of the systems described herein.

[0033] Brief Description of the Drawings

[0034] Embodiments will now be described, purely by way of example, with reference to the accompanying drawings, in which like features are denoted by like reference signs, and in which:

[0035] Figure 1 is a schematic diagram of a system for determining the homogeneity of a material mixture in a volume;

[0036] Figure 2 is a schematic diagram of an alternative implementation of the system shown in Figure 1, in which the acoustic transducers operate in pitch-catch mode;

[0037] Figure 3 is a schematic diagram of an alternative implementation of the system shown in Figure 1, in which a processor is located remotely; Figure 4a is a schematic diagram of an alternative implementation of the system shown in Figure 1, in which the acoustic transducers are located on a conduit;

[0038] Figure 4b is an enlarged view of the conduit shown in Figure 4a;

[0039] Figure 4c is a schematic diagram of an alternative implementation of the conduit shown in Figure 4a, in which the acoustic transducers are located around the external wall of the conduit;

[0040] Figure 4d is a cross-section of the conduit shown in Figure 4c;

[0041] Figure 5 is a schematic diagram of a system for determining the homogeneity of a material mixture in a volume during a high-pressure resin transfer moulding process;

[0042] Figure 6 is a flow diagram of a method of determining the homogeneity of a material mixture in a volume;

[0043] Figure 7 is a flow diagram of a method of mixing and dispensing a material mixture; and

[0044] Figure 8 is a flow diagram of a method of determining the quality of a moulded product.

[0045] Detailed Description

[0046] Figure 1 is a schematic diagram of an example system 100 for determining the homogeneity of a material mixture 110. The system comprises a mixing chamber 101 , which defines an internal volume 102. The mixing chamber 101 comprises two or more (in this case, two) inlets 103, 104. The mixing chamber 101 further comprises one or more (in this case, one) outlets 105. The inlets 103, 104 and outlets are in fluid communication with the internal volume 102 of the mixing chamber 101.

[0047] A material mixture 110, which has two or more components, is formed within the internal volume 102 of the mixing chamber 101. More specifically, a first component 111 of the material mixture 110 enters the volume 102 through the first inlet 103, and a second component 112 of the material mixture 110 enters the volume 102 through the second inlet 104. The first and second components 111 , 112 are injected, or otherwise caused to flow, into the internal volume 102 of the mixing chamber 101. For example, the volume 102 may be at a lower pressure than a source of the first and second components 111, 112 such that the pressure difference causes the components to flow into the volume 102. If the material mixture 110 has more than two components, then each component may enter the volume 102 through additional respective inlets (not shown in Figure 1). Once inside the volume 102, the first and second components 111 , 112 mix with one another to form the material mixture 110. The first and second components 111, 112 may mix through diffusion. Optionally, a mechanical agitator (not shown in Figure 1) may be provided within the volume 102 to assist mixing. The first and second components 111, 112 are fluids, and either may be a solid (e.g., a powder), a liquid or a gas. The material mixture 110 is also a fluid, and is typically a liquid when in the volume 102. The material mixture 110 leaves the volume 102 through the outlet 105. For example, the volume 102 may be at a higher pressure than the outlet 105, such that the pressure difference causes the material mixture 110 to flow out of the volume 102 via the outlet 105. The outlet 105 directs the material mixture 110 to wherever it is to be processed. For example, the outlet 105 may direct the material mixture 110 to a mould (not shown in Figure 1), whereupon the material mixture 110 is shaped before setting or curing.

[0048] The system 100 further comprises two or more (in this case, two) acoustic transducers 120, 130. The purpose of the acoustic transducers 120, 130 is to allow the homogeneity of the material mixture 110 to be determined, as described in more detail below. As shown in Figure 1, the acoustic transducers 120, 130 are positioned outside the mixing chamber 101. More specifically, the acoustic transducers 120, 130 are positioned adjacent a first external wall 106 of the mixing chamber 101. The acoustic transducers 120, 130 are located at different spatial positions of the volume 102, such that each transducer emits acoustic waves into, and receives acoustic waves from, different regions of the volume 102. That is to say, a first acoustic transducer 120 emits acoustic waves into, and receives acoustic waves from, a first region of the volume 102; and a second acoustic transducer 130 emits acoustic waves into, and receives acoustic waves from, a second region of the volume 102. The first acoustic transducer 120 is preferably positioned sufficiently far away from the second acoustic transducer 130 to avoid interference between the acoustic waves they emit, and to prevent one transducer receiving acoustic waves emitted by the other transducer. In practice, the precise locations of the acoustic transducers 120, 130 will depend on various factors such as the geometry of the mixing chamber 101 and the availability of suitable surfaces on which to mount the acoustic transducers 120, 130.

[0049] It is not essential for the acoustic transducers 120, 130 to be positioned outside the mixing chamber 101, and either or both of the acoustic transducers 120, 130 could be positioned within the volume 102 such that they are in contact with the material mixture 110.

[0050] The acoustic transducers 120, 130 are oriented such that, in use, they each emit a respective acoustic wave 122, 132 into the volume 102 and into the material mixture 110, and towards a second external wall 108 of the mixing chamber 101. The second external wall 108 opposes the first external wall 106. Furthermore, the acoustic transducers 120, 130 are oriented such that, in use, they each receive a respective acoustic wave 124, 134 from the volume 102 and from the material mixture 110. As shown in Figure 1, the received acoustic waves 124, 134 are the result of the emitted acoustic waves 122, 132 being reflected by the second external wall 108 of the mixing chamber 101. The measurement setup shown in Figure 1 can thus be said to operate in pulse-echo mode.

[0051] The system 100 further comprises a controller 140. The controller 140 comprises a processor 142, a memory 144, an analogue-to-digital converter (ADC) and a digital-to- analogue converter (DAC). The ADC and DAC are collectively represented by block 146.

[0052] The processor 142 can be any suitable type of data processing device, such as a microprocessor, microcontroller, digital signal processor or application specific integrated circuit (ASIC). The processor 142 is communicatively coupled to the memory 144. The memory 144 can include a volatile memory, a non-volatile memory, or both volatile and non-volatile memories. The memory 144 stores a control program (not shown in Figure 1). The control program includes processor-executable instructions that, when executed by the processor 142, cause the system 100 to perform any of the methods described below with reference to Figures 6 to 8.

[0053] The ADC and DAC 146 are communicatively coupled to each of the acoustic transducers 120, 130. The ADC and DAC are typically coupled to the acoustic transducers 120, 130 by an electrical connection (e.g., using one or more electrically- conducting cables). The DAC converts a digital output from the processor 142 into an analogue electrical signal (e.g., a voltage signal), which is supplied to the acoustic transducers 120, 130. The analogue electrical signal produced by the DAC energises the acoustic transducers 120, 130, causing them to emit acoustic waves 122, 132 into the material mixture 110. The DAC may supply the same signal to both acoustic transducers 120, 130, or may supply a different signal to each acoustic transducer 120, 130. The acoustic transducers 120, 130 generate analogue electrical signals when they receive acoustic waves 124, 134 transmitted through the material mixture 110. The ADC receives an analogue electrical signal from each of the acoustic transducers 120, 130, and produces a digital representation of each analogue signal. More specifically, the ADC outputs a series of digital samples, which are supplied to the processor 142 whereupon they are processed to determine the homogeneity of the material mixture 110 in the volume 102.

[0054] Propagation of the emitted and received acoustic waves 122, 124, 132 and 134 through the volume 102 will be affected by the physical properties of the material mixture 110. For example, the proportion of the first component 111 relative to the second component 112 in the material mixture 110 may influence the speed at which the acoustic waves 122, 124, 132 and 134 propagate through the volume 102. As another example, the proportion of the first component 111 relative to the second component 112 in the material mixture 110 may influence the amount of attenuation experienced by the acoustic waves 122, 124, 132 and 134 as they propagate through the volume 102. As a further example, the proportion of the first component 111 relative to the second component 112 in the material mixture 110 may influence the amount of reflection experienced by the emitted acoustic waves 122, 132 at the interface between the first external wall 106 and the material mixture 110; this in turn will affect the physical properties (e.g., the amplitudes) of the received acoustic waves 124, 134. The homogeneity of the material mixture 110 can be determined by comparing how the acoustic waves are influenced as they are transmitted through different spatial regions of the volume 102. For example, if the material mixture 110 is homogeneous, acoustic waves will have substantially the same speed and / or experience substantially the same attenuation when they propagate through different regions of the volume 102. Conversely, if the material mixture 110 is heterogeneous (i.e., inhomogeneous), acoustic waves will have significantly different speeds and / or experience significantly different attenuation when they propagate through different regions of the volume 102. This principle can be used to determine the homogeneity of the material mixture 110, as will now be described with reference to Figure 6. Figure 6 is a flow diagram of a method 600 of determining the homogeneity of the material mixture 110 in the volume 102.

[0055] The method 600 begins at operation 602, in which the processor 142 causes the first acoustic transducer 120 to emit a first acoustic wave 122 into the volume 102. The processor 142 may cause the first acoustic transducer 120 to emit the first acoustic wave 122 by outputting digital values to the DAC. The digital values represent an excitation waveform which, after digital-to-analogue conversion by the DAC, is received by the first acoustic transducer 120. The excitation waveform causes the first acoustic transducer 120 to emit the first acoustic wave 112 into the volume 102, whereupon it propagates through the material mixture 110. The excitation waveform may be any of a continuous wave, swept frequency wave, or a toneburst excitation.

[0056] In the measurement setup shown in Figure 1 , the first acoustic wave 122 propagates through the material mixture 110 until it reaches the second external wall 108. The first acoustic wave 122 is reflected by the second external wall 108, such that it propagates back towards the first external wall 106 through the material mixture 110. A portion of the reflection of the first acoustic wave is received by the first acoustic transducer 120, and will be referred to as the first received acoustic wave 124. The first received acoustic wave 124 causes the first acoustic transducer 120 to produce an analogue electrical signal.

[0057] At operation 604, the processor 142 receives a first signal that is indicative of the first received acoustic wave 124. For example, the processor 142 may receive a digital signal from the ADC, wherein the digital signal is a digital representation of the analogue electrical signal produced by the first acoustic transducer 120 in response to the first received acoustic wave 124. The processor 142 may store the first signal in the memory 144, such that the stored signal can be processed later to determine the homogeneity of the material mixture 110 as described in more detail in connection with operation 610.

[0058] Operations 608 and 608 are substantially the same as operations 602 and 604, respectively, but are performed with respect to a second acoustic transducer 130. As mentioned above, the first and second acoustic transducers 120, 130 are located at different spatial positions with respect to the volume 102. In more detail, at operation 606, the processor 142 causes the second acoustic transducer 130 to emit a second acoustic wave 132 into the volume 102. The processor 142 may cause the second acoustic transducer 130 to emit the second acoustic wave 132 by outputting digital values to the DAC. The digital values represent an excitation waveform which, after digital-to-analogue conversion by the DAC, is received by the second acoustic transducer 130. The excitation waveform causes the second acoustic transducer 130 to emit the second acoustic wave 132 into the volume 102, whereupon it propagates through the material mixture 110. The excitation waveform may be any of a continuous wave, swept frequency wave, or a toneburst excitation.

[0059] In the measurement setup shown in Figure 1 , the second acoustic wave 132 propagates through the material mixture 110 until it reaches the second external wall 108. The second acoustic wave 132 is reflected by the second external wall 108, such that it propagates back towards the first external wall 106 through the material mixture 110. A portion of the reflection of the second acoustic wave is received by the second acoustic transducer 130, and will be referred to as the second received acoustic wave 134. The second received acoustic wave 134 causes the second acoustic transducer 130 to produce an analogue electrical signal.

[0060] At operation 608, the processor 142 receives a second signal that is indicative of the second received acoustic wave 134. For example, the processor 142 may receive a digital signal from the ADC, wherein the digital signal is a digital representation of the analogue electrical signal produced by the second acoustic transducer 130 in response to the second received acoustic wave 134. The processor 142 may store the second signal in the memory 144, such that it can be processed later to determine the homogeneity of the material mixture 110.

[0061] At operation 610, the processor 142 compares the first signal with the second signal to determine the homogeneity of the material mixture 110 in the volume 102. More specifically, one or more properties of the first and second signals are compared to determine whether the material mixture 110 is homogeneous. When the comparison reveals that the one or more properties of the first and second signals are substantially the same, the material mixture 110 is homogeneous. However, when the comparison reveals that the one or more properties of the first and second signals are substantially different, the material mixture 110 is heterogeneous.

[0062] In one implementation, times of flight associated with the first and second signals are compared. The time of flight of the acoustic waves 122, 124 associated with the first signal can be estimated by calculating the time elapsed between the first acoustic wave 122 being emitted at operation 602 and the first signal being received at operation 604. Similarly, the time of flight of the acoustic waves 132, 134 associated with the second signal can be estimated by calculating the time elapsed between the second acoustic wave 132 being emitted at operation 606 and the second signal being received at operation 608. When the time of flight associated with the first signal differs from the time of flight associated with the second signal, it can be inferred that the material mixture 110 is heterogeneous. In other words, the difference in the times of flight indicates that the composition of the material mixture 110 (and, hence, the speed of sound in the material mixture 110) differs between a first region of the volume 102 through which acoustic waves 122, 124 propagate and a second region of the volume 102 through which acoustic waves 132, 124 propagate; this difference in the composition means that the material mixture 110 is, by definition, heterogeneous. The amount by which the time of flight associated with the first signal differs from the time of flight associated with the second signal is indicative of the extent to which the material mixture 110 is heterogeneous.

[0063] In another implementation, the amplitudes of the first and second signals are compared. In this implementation, the amplitude of the first emitted acoustic wave 122 is the same as that of the second emitted acoustic wave 132. When the amplitude of the first signal differs from the amplitude of the second signal, it can be inferred that the material mixture 110 is heterogeneous. In other words, the difference in the amplitudes indicates that the composition of the material mixture 110 (and, hence, the extent to which the material mixture 110 attenuates acoustic waves) differs between a first region of the volume 102 through which acoustic waves 122, 124 propagate and a second region of the volume 102 through which acoustic waves 132, 124 propagate; this difference in the composition means that the material mixture 110 is, by definition, heterogeneous. The amount by which the amplitude of the first signal differs from the amplitude of the second signal is indicative of the extent to which the material mixture 110 is heterogeneous. In yet another implementation, times of flight associated with the first and second signals and the amplitudes of the first and second signals are compared to determine the homogeneity of the material mixture 110.

[0064] In order to improve the accuracy of the determination of the homogeneity of the material mixture 110 in the volume 102, a statistical analysis can be used to compare the first and second signals in operation 610. Statistical analyses have the advantage of allowing multiple signals from each of the first and second acoustic transducers 120, 130 to be considered. Non-limiting examples of suitable statistical analysis techniques include:

[0065] • Coefficient of variation analysis: this technique compares the standard deviation of measurements (e.g., time of flight and / or amplitude) made by the first and second acoustic transducers 120, 130 with the average value of the measurements. A low coefficient of variation indicates that the material mixture 110 is homogeneous, whereas a high coefficient of variation indicates that the material mixture 110 is heterogeneous.

[0066] • Correlation analysis: this technique measures the strength of the relationship between the measurements (e.g., time of flight and / or amplitude) made by the first and second acoustic transducers 120, 130. A strong positive correlation indicates that the material mixture 110 is homogeneous, whereas a weak or negative correlation indicates that the material mixture 110 is heterogeneous.

[0067] • Cluster analysis: this technique groups the measurements (e.g., time of flight and / or amplitude) made by the first and second acoustic transducers 120, 130 based on their similarity. If the measurements cluster together, the material mixture 110 is homogeneous. Conversely, if the measurements are dispersed, the material mixture 110 is heterogeneous.

[0068] • Principal component analysis: this technique identifies underlying patterns in the measurements (e.g., time of flight and / or amplitude) made by the first and second acoustic transducers 120, 130. A simple pattern indicates that the material mixture 110 is homogeneous, whereas a complex pattern indicates that the material mixture 110 is heterogeneous.

[0069] The operations of the method 600 need not be performed in exactly the order shown in Figure 6, but can be performed in a different order that achieves substantially the same result. For example, operations 602 and 606 can be performed at substantially the same time (that is, the first and second acoustic transducers 120, 130 can emit acoustic waves into the volume at substantially the same time). Similarly, operations 604 and 608 can be performed at substantially the same time (that is, signals can be received from the first and second acoustic transducers 120, 130 at substantially the same time). As another example, operation 606 can be performed before operation 604. Operations 602 and 606 are optional, in the sense that neither operation forms an essential feature of the subject-matter for which protection is sought.

[0070] The determination of homogeneity which results from method 600 can optionally be used to determine when the material mixture 110 is ready to be dispensed from the mixing chamber 101. Figure 7 is a flow diagram of a method 700 of mixing and dispensing the material mixture 110.

[0071] The method 700 begins at operation 702, in which the homogeneity of the material mixture 110 in the volume 102 is determined. The homogeneity of the material mixture 110 can be determined by performing method 600.

[0072] At operation 704, the homogeneity determined at operation 702 is compared with a threshold to determine whether the material mixture 110 is sufficiently homogeneous. When the homogeneity is greater than or equal to the threshold, the material mixture 110 is ready to be dispensed from the mixing chamber 101 and the method proceeds to operation 706. When the homogeneity is less than the threshold, the material mixture 110 is not ready to be dispensed from the mixing chamber 101 and the method proceeds to operation 708. The precise level of the threshold will depend on the purpose for which the material mixture 110 is to be used. For example, a relatively high threshold may be used when the material mixture 110 is to be used to manufacture a composite material that has a safety-critical role (e.g., a component of an aircraft), whereas a relatively low threshold may be used when the material mixture 110 is to be used to manufacture a low-value consumer product. At operation 706, the material mixture 110 is dispensed from the mixing chamber 110. For example, the controller 140 may cause an electrically-activated valve on the outlet 105 to be opened, such that the material mixture 110 is able to leave the mixing chamber 110. The material mixture 110 may be dispensed into a mould or a container. Alternatively, the material mixture 110 may be dispensed into another apparatus, whereupon the material mixture 110 undergoes further processing.

[0073] At operation 708, the material mixture 110 is mixed. For example, the controller 140 may cause a mechanical agitator to mix the material mixture 110. As another example, the controller 140 may simply wait for a period of time to allow diffusion of the first and second components 111, 112 of the material mixture 110. The method 700 then returns to operation 702 for a further iteration.

[0074] The method 700 can be used in mix, meter and dispense (MMD) composite manufacture, to determine whether two (or more) component materials (e.g., a resin and a catalyst / hardener) are thoroughly mixed before mixture has cured. The method 700 can be used in other manufacturing processes, particularly those where the quality of a finished product is dependent upon the homogeneity of a mixture of component materials.

[0075] The methods 600, 700 can be performed by systems other than the system 100 shown in Figure 1. Non-limiting examples of other systems by which the methods 600, 700 can be performed will now be discussed with reference to Figures 2 to 5.

[0076] Figure 2 is a schematic diagram of another example system 200 for determining the homogeneity of a material mixture 110. The system 200 shown in Figure 2 differs from the system 100 shown in Figure 1 in that the system 200 operates in pitch-catch mode whereas the system 100 operates in pulse-echo mode.

[0077] The system 200 comprises four or more (in this case, four) acoustic transducers 220, 226, 230, 236. As shown in Figure 1, the acoustic transducers 220, 226, 230, 236 are positioned outside the mixing chamber 101. More specifically, a first acoustic transducer 226 and a second acoustic transducer 236 are positioned adjacent the second external wall 108 of the mixing chamber 101. A third acoustic transducer 220 and a fourth acoustic transducer 230 are positioned adjacent the first external wall 106 of the mixing chamber 101. The first and third acoustic transducers 226, 220 are oriented such that, in use, the third acoustic transducer 220 emits an acoustic wave 222 into the volume 102 and into the material mixture 110, and towards the first acoustic transducer 226. Similarly, the second and fourth acoustic transducers 236, 230 are oriented such that, in use, the fourth acoustic transducer 230 emits an acoustic wave 232 into the volume 102 and into the material mixture 110, and towards the second acoustic transducer 236. The first and third acoustic transducers 226, 220 are located at different spatial positions of the volume 102 with respect to the second and fourth acoustic transducers 236, 230, such that each pair of transducers emits acoustic waves into, and receives acoustic waves from, different regions of the volume 102. It is not essential for the acoustic transducers 220, 226, 230, 236 to be positioned outside the mixing chamber 101, however, and any or all of the acoustic transducers 220, 226, 230, 236 could be positioned within the volume 102 such that they are in contact with the material mixture 110. The acoustic transducers 220, 226, 230, 236 are all communicatively coupled to the ADC and DAC 146, but the connections to transducers 226, 236 are not shown in Figure 2 for the sake of visual clarity. The system 200 is otherwise substantially the same as the system 100 described in relation to Figure 1.

[0078] When the system 200 is used to perform the method 600, at operation 602 the processor 142 causes the third acoustic transducer 220 to emit a first acoustic wave 222 into the volume 102. The first acoustic wave 222 propagates through the material mixture 110 until it reaches the first acoustic transducer 226, causing the first acoustic transducer 226 to produce an analogue electrical signal. At operation 604, the processor 142 receives a first signal that is indicative of the first acoustic wave 222. For example, the processor 142 may receive a digital signal from the ADC, wherein the digital signal is a digital representation of the analogue electrical signal produced by the first acoustic transducer 226 in response to the first acoustic wave 222. At operation 606, the processor 142 causes the fourth acoustic transducer 230 to emit a second acoustic wave 232 into the volume 102. The second acoustic wave 232 propagates through the material mixture 110 until it reaches the second acoustic transducer 236, causing the second acoustic transducer236 to produce an analogue electrical signal. At operation 608, the processor 142 receives a second signal that is indicative of the second acoustic wave 232. For example, the processor 142 may receive a digital signal from the ADC, wherein the digital signal is a digital representation of the analogue electrical signal produced by the second acoustic transducer 236 in response to the second acoustic wave 232. At operation 610, the processor 142 compares the first signal with the second signal to determine the homogeneity of the material mixture 110 in the volume 102 as previously described.

[0079] Figure 3 is a schematic diagram of another example system 300 for determining the homogeneity of a material mixture 110. The system 300 shown in Figure 3 differs from the system 100 shown in Figure 1 in that the system 300 processes the received signals remotely. System 300 is otherwise substantially the same as system 100.

[0080] In system 300, the ADC and DAC 146 are not physically co-located with a controller 340. Instead, the ADC and DAC 146 exchange data with the controller 340 via a network 350. The network 350 may comprise a local area network (LAN), a wide area network (WAN) or a combination thereof. The ADC and DAC 146 and the controller 340 may each be communicatively coupled to the network 350 by a respective network interface (not shown in Figure 3). The network interfaces may be wired or wireless interfaces, and may use any suitable communication protocol(s).

[0081] When the system 300 is used to perform the method 600, at operations 602 and 606 the controller 340 causes the first and second acoustic transducers 120, 130 to emit acoustic waves by transmitting digital representations of excitation signals to the DAC via the network 350. The DAC converts the digital representations of the excitation signals to analogue voltages, which are applied to the first and second acoustic transducers 120, 130 to cause them to emit first and second acoustic waves 122, 132, respectively, into the volume 102. At operations 604 and 604, the controller 340 receives first and second signals from the first and second acoustic transducers 120, 130, respectively, via the ADC and the network 350. The method 600 is otherwise performed by system 300 in substantially the same way as previously described with reference to system 100.

[0082] Figure 4a is a schematic diagram of another example system 400 for determining the homogeneity of a material mixture 110. The system 400 shown in Figure 4a differs from the system 100 shown in Figure 1 in that the acoustic transducers are located on a conduit 450. That is, the system 400 determines the homogeneity of the material mixture 110 in the conduit 450, rather than in the mixing chamber 101. Determining the homogeneity of the material mixture 110 in the conduit 450 is advantageous when the mixing chamber 101 has an irregular geometry that prevents comparable measurements being made using acoustic transducers sited at different positions.

[0083] The conduit 450 is coupled to the outlet 105 of the mixing chamber 101, such that the homogeneity of the material mixture 110 is measured after it leaves the mixing chamber 101. As shown in Figure 4a, the conduit 450 is positioned between the mixing chamber 102 and a mould 460. Hence, the homogeneity of the material mixture 110 within the mould 460 can be inferred from its homogeneity in the conduit 450.

[0084] Figure 4b is an enlarged view of the conduit 450 shown in Figure 4a. The conduit 450 comprises a wall 406, which in this case has a circular cross-section. The conduit 450 has an internal volume 402, which is at least partly defined by the internal surface of the wall 406, the end of the outlet 105 of the mixing chamber 101 and the inlet to the mould 460. The conduit 450 has a circular cross-section in the example shown, but other cross-sectional shapes are possible.

[0085] Two or more (in this case, two) acoustic transducers 420, 430 are positioned outside the conduit 450. More specifically, the acoustic transducers 420, 430 are positioned on the external surface of the wall 406 of the conduit 450. The acoustic transducers 420, 430 are located at different spatial positions of the volume 402, such that each transducer emits acoustic waves into, and receives acoustic waves from, different regions of the volume 402. That is to say, a first acoustic transducer 420 emits acoustic waves 422 into, and receives acoustic waves 424 from, a first region of the volume 402; and a second acoustic transducer 430 emits acoustic waves 432 into, and receives acoustic waves 434 from, a second region of the volume 402. The first acoustic transducer 420 can be positioned sufficiently far away from the second acoustic transducer 430 to avoid interference between the acoustic waves they emit, and to prevent one transducer receiving acoustic waves emitted by the other transducer. It is not essential for the acoustic transducers 420, 430 to be positioned outside the conduit 450, and either or both of the acoustic transducers 140, 430 could be positioned within the volume 402 such that they are in contact with the material mixture 110. Although Figures 4a and 4b show the first acoustic transducer 420 positioned upstream of the second acoustic transducer 430, it is not essential for the acoustic transducers to be arranged in this manner. Figures 4c and 4d show a different arrangement of acoustic transducers, in which the first and second acoustic transducer 420, 430 are located at substantially the same point along the length of the conduit 450 but have different orientations. Figure 4c is a side view of the conduit 450, and Figure 4d is a cross-section through the plane A-A indicated in Figure 4c.

[0086] As shown in Figures 4c and 4d, the first transducer 420 is oriented at ninety degrees with respect to the second transducer 430. However, other orientations are possible. For example, if three acoustic transducers are used, the acoustic transducers may be oriented at 120 degrees with respect to one another. Arrangements such as that shown in Figures 4c and 4d are beneficial when the conduit 450 is too short to locate one acoustic sensor upstream of the other acoustic sensor.

[0087] It is possible to combine the arrangements shown in Figures 4a and 4b with the arrangements shown in Figures 4c and 4d, such that two or more acoustic transducers are located at each of a plurality of points along the length of the conduit 450. At each point, the two or more transducers have different orientations.

[0088] The system 400 can be used to perform the method 600 in substantially the same way as previously described with reference to the system 100 shown in Figure 1. However, when the system 400 is used, acoustic waves 422, 432 are transmitted into the internal volume 402 of the conduit 450. Similarly, acoustic waves 424, 434 are received from the internal volume 402 of the conduit 450.

[0089] As shown in Figures 4b to 4d, the two acoustic transducers 420, 430 are configured to operate in pulse-echo mode. However, the conduit 450 could instead be provided with four or more acoustic transducers configured to operate in pitch-catch mode.

[0090] The systems 100, 200, 300, 400 may be part of a low-pressure resin transfer moulding apparatus. In this case, the first component 111 may be a resin, and the second component 112 may be a catalyst or hardener. After being mixed in the mixing chamber 101 , the material mixture 110 is injected into a mould (such as mould 460 shown in Figure 4a). In the mould, the material mixture 110 cures to form a product. The mould may optionally contain a reinforcement (such as carbon fibres or glass fibres), which is covered by the injected material mixture 110.

[0091] Figure 5 is a schematic diagram of another example system 500 for determining the homogeneity of a material mixture 110. The system 500 shown in Figure 5 differs from the system 200 shown in Figure 2 in that the mixing chamber 501 of system 500 does not have an outlet.

[0092] System 500 represents a measurement setup suitable for use with a high-pressure resin transfer moulding process. In high-pressure resin transfer moulding, a first component 111 and a second component 112 of a material mixture 110 are injected at high pressure (e.g., greater than 100 bar) into the mixing chamber 501. The high pressure at which the first and second components 111 , 112 are injected removes the need for mechanical agitation of the material mixture 110. The mixing chamber 501 also serves as a mould for the product produced from the material mixture 110. Hence, the material mixture 110 remains within the internal volume 502 of the mixing chamber 501 until it has cured, rather than being dispensed from the mixing chamber 501. The mixing chamber 501 may thus have the shape of the product to be produced by the high-pressure resin transfer moulding process. The first component 111 may be a resin, and the second component 112 may be a catalyst or hardener. The mould may optionally contain a reinforcement (such as carbon fibres or glass fibres), which is covered by the material mixture 110.

[0093] The system 500 can be used to perform the method 600 in substantially the same way as discussed above in relation to the system 200 shown in Figure 2. The homogeneity of the material mixture 110 within the volume 502 directly impacts the quality of the product produced when the material mixture 110 cures. The determination of homogeneity which results from method 600 can optionally be used to determine whether the material mixture 110 is sufficiently homogeneous to produce a product of acceptable quality. Figure 8 is a flow diagram of a method 800 of determining the quality of a moulded product formed from a material mixture 110.

[0094] The method 800 begins at operation 802, in which the homogeneity of the material mixture 110 in the volume 502 is determined. The homogeneity of the material mixture 110 can be determined by performing method 600. At operation 804, the homogeneity determined at operation 802 is compared with a threshold to determine whether the material mixture 110 is sufficiently homogeneous. When the homogeneity is greater than or equal to the threshold, the material mixture 110 is deemed to be sufficiently homogeneous for the resulting product to be of acceptable quality (see operation 806). When the homogeneity is less than the threshold, the material mixture 110 is deemed to be too heterogeneous for the resulting product to be of acceptable quality (see operation 808). The precise level of the threshold will depend on the nature and purpose of the product formed by the material mixture 110. For example, a relatively high threshold may be used when the product has a safety-critical role (e.g., a component of an aircraft), whereas a relatively low threshold may be used for a low-value consumer product.

[0095] As shown in Figure 5, the system 500 comprises four acoustic transducers 220, 226, 230, 236 configured to operate in pitch-catch mode. However, the system 500 could instead have two or more acoustic transducers configured to operate in pulse-echo mode.

[0096] The systems 200, 400, 500 shown in Figures 2, 4a and 5 can be modified to process the received signals remotely, in a similar manner to that disclosed in connection with Figure 3.

[0097] The systems 100, 200, 300, 400, 500 shown in Figures 1 to 5 all determine homogeneity by sampling a material mixture 110 at two spatial positions of a volume. Any of these systems can be modified to include additional acoustic transducers, so as to allow the material mixture 110 to be sampled at more than two spatial positions of the volume. By increasing the number of spatial positions at which acoustic transducers are located, a more complete understanding of homogeneity throughout the whole of the volume can be achieved.

[0098] Although Figures 1 to 5 depict the acoustic transducers as discrete and separate components, the acoustic transducers can be implemented using an array of acoustic transducers. For example, acoustic transducers 120, 130 shown in Figures 1 and 3 may be implemented by different elements of an array of acoustic transducers. As another example, acoustic transducers 220, 230 shown in Figures 2 and 5 may be implemented by different elements of a first array of acoustic transducers and / or acoustic transducers 226, 236 may be implemented by different elements of a second array of acoustic transducers. An array of acoustic transducers may be configured to operate in pulse-echo mode or in pitch-catch mode. The use of an array of acoustic transducers can allow the number of spatial positions at which acoustic transducers are located to be easily increased, thus allowing a more complete understanding of homogeneity throughout the whole of the volume can be achieved. The use of an array of acoustic transducers may also allow beamforming techniques to be used, which in turn can allow different regions of the volume to be sampled.

[0099] The systems 100, 200, 300, 400, 500 and the methods 600, 700, 800 can be used for a variety of applications, in addition to the resin transfer moulding processes discussed previously. In particular, the systems and methods disclosed herein can be applied to other manufacturing processes in which it is desirable to ensure component materials are homogeneously mixed. For example, the systems and methods disclosed herein can be used in extrusion, injection moulding and casting processes. In the case of extrusion, a material to be extruded is mixed within the mixing chamber 101 and, when it is determined to be sufficiently homogeneous, the material mixture 110 is dispensed via the outlet 105 and forced through a die to form an extruded product. In the case of injection moulding and casting, a material to be moulded or cast is mixed within the mixing chamber 101 and, when it is determined to be sufficiently homogeneous, the material mixture 110 can be dispensed via the outlet 105 into a mould or die. The systems and methods disclosed herein can be also used in coating processes. In this case, a coating material (such as a paint, adhesive or protective coating) is mixed within the mixing chamber 101 and, when it is determined to be sufficiently homogeneous, dispensed via the outlet 105 and applied to a surface using a sprayer. The systems and methods disclosed herein can be also used in mixing or blending processes. In this case, two or more materials are mixed or blended within the mixing chamber 101 and, when the material mixture 110 is determined to be sufficiently homogeneous, it is dispensed via the outlet 105 and optionally used as a raw material for another manufacturing process.

[0100] The methods 600, 700, 800 can be implemented by instructions stored on a processor- readable medium. The processor-readable medium may be: a read-only memory (including a PROM, EPROM or EEPROM); a random access memory; a flash memory; an electrical, electromagnetic or optical signal; a magnetic, optical or magneto-optical storage medium; one or more registers of a processor; or any other type of processor- readable medium. The methods 600, 700, 800 and / or the functionality of the processor 142 can be implemented by hardware, firmware, software or any combination thereof. Such hardware may include one or more application-specific integrated circuits or appropriately connected discrete logic gates. A hardware description language can be used to implement the methods 600, 700, 800 and / or the functionality of the processor 142 with dedicated hardware. It will be understood that the invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the claims.

Claims

Claims1. A method of determining homogeneity of a material mixture in a volume, the method comprising: receiving a first signal, from a first acoustic transducer at a first spatial position of the volume, indicative of an acoustic wave transmitted through the material mixture at the first spatial position of the volume; receiving a second signal, from a second acoustic transducer at a second spatial position of the volume, indicative of an acoustic wave transmitted through the material mixture at the second spatial position of the volume; and comparing the first and second signals to determine the homogeneity of the material mixture within the volume.

2. A method in accordance with claim 1 , wherein the method further comprises causing acoustic transducers to emit acoustic waves into the volume.

3. A method in accordance with claim 1 or claim 2, wherein comparing the first and second signals comprises using a statistical analysis.

4. A method in accordance with claim 3, wherein the statistical analysis comprises one or more of: a coefficient of variation comparison analysis; a correlation analysis; a cluster analysis; and a principal component analysis.

5. A method in accordance with any of the preceding claims, further comprising determining whether the homogeneity of the material mixture falls within an acceptable homogeneity threshold.

6. A method in accordance with claim 5, further comprising continuing a mixing process of the material mixture if the homogeneity of the material mixture falls outside of the acceptable homogeneity threshold.

7. The method in accordance with claim 5 or claim 6, further comprising dispensing the material mixture if the homogeneity of the material mixture falls within the acceptable homogeneity threshold.

8. A computer program comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out the method of any preceding claim.

9. A computer-readable medium comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out a method in accordance with any of claims 1 to 7.

10. A system for determining homogeneity of a material mixture in a volume, the system comprising: a volume for receiving the material mixture; a first acoustic transducer positioned adjacent the volume at a first spatial position, the first acoustic transducer being configured to produce a first signal indicative of an acoustic wave transmitted through the material mixture and received at the first acoustic transducer; a second acoustic transducer positioned adjacent the volume at a second spatial position, the second acoustic transducer being configured to produce a second signal indicative of an acoustic wave transmitted through the material mixture and received at the second acoustic transducer; and a processor configured to: receive the first and second signals from the first and second acoustic transducers, respectively; and compare the first and second signals to determine the homogeneity of the material mixture within the volume.

11. A system in accordance with claim 10, further comprising an array of acoustic transducers, the array of acoustic transducers comprising the first and second acoustic transducers, wherein each of the acoustic transducers is positioned adjacent the volume at a different spatial position of the volume and configured to: produce a signal indicative of an acoustic wave transmitted through the material mixture at a respective spatial position of the volume; and / or emit an acoustic wave into the material mixture.

12. A system in accordance with claim 11, wherein the processor is further configured to:receive the signal from each acoustic transducer of the array of acoustic transducers; and compare the signals to determine the homogeneity of the material mixture within the volume.

13. A system in accordance with any of claims 10 to 12, wherein the processor is further configured to cause the first and second acoustic transducers to emit acoustic waves into the volume.

14. A system in accordance with any of claims 10 to 13, wherein the volume comprises one or more of: a mixing chamber; a conduit; and a mould.

15. A system in accordance with claim 14, wherein the volume comprises the conduit, the conduit being disposed between a mixing chamber and a mould.

16. A system in accordance with claim 14 or claim 15, wherein the volume comprises the conduit, and wherein the first and second acoustic transducers are located at different points along a length of the conduit.

17. A system in accordance with claim 14 or claim 15, wherein the volume comprises the conduit, wherein the first and second acoustic transducers are located at substantially the same point along a length of the conduit, and wherein the first acoustic transducer has a different orientation with respect to the second acoustic transducer.

18. A system in accordance with any of claims 11 to 17, wherein the processor is located remotely from the first and second acoustic transducers and the volume.

19. A kit of parts for determining the homogeneity of a material mixture in a volume, the kit of parts comprising: a first acoustic transducer configured to emit a first signal indicative of an acoustic wave transmitted through the material mixture at a first spatial position of the volume;a second acoustic transducer configured to emit a second signal indicative of an acoustic wave transmitted through the material mixture at a second spatial position of the volume; and a processor connectable to the first and second acoustic transducers, the processor being configured to: receive the first and second signals; and compare the first and second signals to determine the homogeneity of the material mixture within the volume.

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