FIELD

This disclosure relates generally to methods of controlling presses, particularly presses capable of pressuring capsules to ultra-high pressures, and to press systems configured to be capable of such control.

BACKGROUND

United States patent number 6,336,802 discloses a unitary frame and unitary cartridge with internal intensification.

There is a need for an ultra-high pressure press apparatus having well controlled pressure generation. SUMMARY

Viewed from a first aspect there is provided a method of controlling a press apparatus suitable for pressurising a capsule to at least one gigapascal (GPa), the press apparatus comprising a frame suitable for accommodating the capsule and at least four load devices, each securable in relation to the frame and capable of applying variable load onto the capsule in response to control of a first and / or a second variable operating parameter; measurement mechanisms for measuring the values of first and second operating parameters in respect of each of the load devices; and a control mechanism for controlling (the load application operation of) each load device according to a set-point for the first or the second operating parameter; the method including controlling a first of the load devices according to a set-point of the first operating parameter; measuring the second operating parameter in respect of the first load device; and controlling a second of the load devices (or each of all of the other load devices) according to the measured second operating parameter in respect of the first load device.

Various arrangements and combinations are envisaged for example press apparatuses, methods of controlling them and methods of using them.

In some examples, each load device may comprise a ram capable of reciprocating within a chamber of a hydraulic cylinder in response to a hydraulic ram displacement mechanism (in other words, a hydraulic mechanism capable of causing displacement of the ram within the chamber, displacing the ram away from the from the chamber or retracting it into the chamber); and the first and second operating parameters are selected from the relative displacement of the ram or a component that will move in response to displacement of the ram, and the pressure of hydraulic fluid contained within the hydraulic cylinder. In some examples, the first and second operating parameters may be selected additionally from operating parameters for a mechanism of changing the pressure of the hydraulic fluid contained within the cylinder; and in some examples, the first and second operating parameters may be selected additionally from a rate of change of mass of hydraulic fluid contained within the hydraulic cylinder, a rate of pumping hydraulic fluid into or from the cylinder, a displacement of an intensifier member capable of reciprocating within the chamber operative to urge the ram to move and / or to apply load to the capsule. In some examples, each load device may comprise a displacement transducer arranged for measuring the displacement of a ram or other component that will be urged to move in response to displacement of a ram, such as an anvil that may be coupled to the ram. In some examples, each load device may comprise a pressure transducer arranged for measuring the pressure of hydraulic fluid contained within the hydraulic cylinder.

In some examples, the method may include crystallising or sintering grains of diamond of cubic boron nitride (cBN). In some examples, the capsule may contains hBN and may be configured for the synthesis of cBN, or sintering polycrystalline cubic boron nitride (PCBN) material; or the capsule may contain a source of carbon and may be configured for the synthesis of synthetic diamond or sintering of polycrystalline diamond (PCD) material.

In general, it may not be possible to calculate or derive the first and second operating parameters form each other, since the relationship between their values will generally depend on the response of the capsule to the applied load and the temperature, the effects of which will generally be inter-related and may be non-linear. For example, material comprised in a capsule may undergo a phase change or chemical reaction at particular combinations of pressure and temperature, neither of which may be sufficiently accurately measurable when the pressure exceeds about 1 GPa (ultra-high pressure). Therefore, displacement of a ram comprised in a hydraulic cartridge may not correspond to proportional changes in pressure of the capsule or the hydraulic fluid. In general, displacement of the ram, for example, will be influenced by the pressure of the hydraulic fluid as well as the pressure within the capsule and the potentially changing configuration of the capsule at ultra-high pressure and high temperature. Therefore, it will likely be necessary to measure the values of both the first and second operating parameters, such as the displacement of a moveable member such as a ram or the pressure of the hydraulic fluid, or other parameters from each of these can be derived.

For example, in a process of synthesising diamond or cubic boron nitride (cBN) crystals or sintering aggregation of diamond or cBN grains, a suitable capsule may be subject to pressurisation according to a desired capsule loading and heating profile. A loading profile may comprise a sequence of changes over time of the load applied to the capsule, or to the pressure of hydraulic fluid driving a ram, for example. A heating profile may comprise a sequence of electrical power values applied over time to the capsule to generate heat within it. The loading and heating profile may be plotted as graphs versus time and may be configured to achieve a desired pressurisation and heating profile for the capsule in order to crystallise or sinter cBN or diamond grains. Since it may be very impractical to measure the actual temperature and pressure within the capsule during an ultra-high pressure, high temperature manufacturing process, these may be controlled indirectly, by measuring and controlling certain operating parameters of the load devices, such as the hydraulic cartridges. Some example methods may include switching control of the load devices during a pressurisation process, such that the first load device becomes controlled according to a series of set points for the second operating parameter, and the second load device becomes controlled according to the measured values of the first operating parameter of the first load device. In some examples, a crystallisation or sintering process may be controlled differently at different stages of the process; for example, in one stage of the process, the first operating parameter may be the pressure of the hydraulic fluid driving a ram, and then in a subsequent stage, the first operating parameter may be the displacement of the ram. In another example, the displacement of the ram may initially be used as the first operating parameter and subsequently the pressure of the hydraulic fluid may be used as the first operating parameter. A change in the first and second operating parameters during a process may be triggered by the lapse of a particular time period, by some measured response of the capsule or by a particular change in one of the first or second operating parameters, such as the rate of change (velocity) of the displacement of the ram exceeding a certain value, or a sudden change in the pressure of hydraulic fluid.

Some example methods may include measuring the difference between the respective values of the first or second operating parameters measured in respect of two or more of the load devices, and reducing the load applied onto the capsule, or aborting the pressurisation process if the difference is at least a critical value. The critical value will likely depend on the configuration of the press apparatus and the nature of the pressurisation process, and may correspond to a state in which the process will likely fail or the press apparatus become damaged. In some examples, the frame may comprise a plurality of segments, each configured for accommodating a respective load device and such that the segments can be coupled to each other (the frame may be referred to as a 'linked frame') with sufficient strength to withstand the reaction forces associated with pressurisation of the capsule. For example, the segments may be configured such that they can be coupled to each other by pins or rods. In other examples, the frame may comprise or consist of a unitary, single body, which may comprise or consist of forged steel. Unitary frames may have the aspect of retaining their configuration more reliably in use, deforming to a lesser extent and / or in a more repeatable way than segmented frames may likely behave in use.

In some examples, the set-point of the first and / or second operating parameter may vary with time.

In some examples, the capsule may be pressurised at a pressure of at least about 5 GPa, at least about 6 GPa, or at least about 7 GPa.

In some examples, the press apparatus may comprise six load devices (and no more or fewer) attached or attachable in relation to six respective sides or segments of the frame, in which the frame and load devices are configured to be capable of applying load from six directions onto the capsule located at the centre of the frame (such press apparatuses may be described as 'cubic' presses, having generally cubic symmetry).

In some examples, the press apparatus may comprise four load devices (and no more or fewer) attached or attachable to (or attached or attachable to) four respective sides of the frame (such press apparatuses may be described as 'tetrahedral' presses, having generally tetrahedral symmetry).

In some examples, each load device can urge a respective anvil to move in response to a first and a second displacement mechanism; and the method may include locating the capsule against a respective bearing end surface of each of a first set of at most three anvils (for example, one, two or three anvils, arranged adjacently) arranged to be capable of supporting the capsule against gravity (at least one of these anvils will be located underneath the capsule in relation to the gravitational force), the anvils of the first set thus being in their respective initial positions in contact with the capsule; using the first displacement mechanism to move each of a second set of at least one anvil into an intermediate position, in which respective bearing end surfaces of the or each anvil of the second set is spaced apart from the capsule; using the second displacement mechanism to move the or each anvil of the second set into a respective initial position in contact with the capsule; measuring initial values of the first or second operating parameter in respect of each of each anvils in its respective initial position; and controlling the first or second operating parameter in respect of each of the anvils, treating the set-point in each case as being relative to the respective initial value (in other words, thus calibrating the operating parameters corresponding to the effective 'zero' value in relation to which the operating parameters will be controlled according to the set points).

In some examples, the intermediate positions may be such that the spacing between the end surfaces of the anvils and the capsule are about 0.2 to about 2 mm.

In some examples, each load device may comprise a ram capable of reciprocating within a chamber of an hydraulic cylinder in response to hydraulic fluid being pumped into or from the chamber; and each load device may comprises an intensifier member capable of reciprocating within the chamber, configured such that the ram can be urged to reciprocate within the chamber in response to reciprocation of the intensifier member within the chamber when the chamber is filled with hydraulic fluid. The first displacement mechanism may be used to move at least one of the anvils into the intermediate position and the second displacement mechanism may be used to move the anvil to an initial position in contact with the capsule with sufficiently low force to avoid substantial crushing of the capsule. Movement of the intensifier member may be effected by an electrical and / or mechanical mechanism. Some example methods may include disengaging the second displacement mechanism when then pressure in the hydraulic fluid increases as a result of contact between the anvil and the capsule. Each of the anvils may be positioned thus in sequence or simultaneously.

Once all six anvils have been set in their initial positions, the displacement and / or the load transducers may be in effect set at zero in control software. Subsequent net anvil displacement may be calculated by subtracting the initial displacement value from subsequently measured displacement. Similarly, the pressure of the hydraulic fluid in the anvils may be regarded as base pressures, and subsequent effective pressures determined by subtracting the base pressure from pressure measured by the pressure transducers.

Example methods may have the aspect of enabling substantially greater control of the pressurisation of a capsule using a press apparatus comprising a segmented frame, since enhanced control of the loading of the capsule may substantially compensate for the potentially higher degree and repeatability or predictability of the distortion of the frame in use. In some examples, a relatively low cost press may in effect be enhanced by using an example method, since the method may likely enable a process to be better controlled. Good control of the ultra-high pressurisation and heating of a capsule may be particularly useful for the crystallisation or sintering of cBN grains, and examples of the method may have the aspect of enabling segmented frame presses to be used to manufacture cBN grains or sintered bodies more reliably. Examples of the method may enable PCD or cBN or other sintered bodies to be manufactured more reliably at ultra-high pressures, particularly sintered bodies having relatively complex configuration, such as tubular or dome-shaped bodies. Disclosed example methods will also likely have the aspect of enabling greater control of processes in which a unitary press frame is used. Viewed from a second aspect, there is provided a method of controlling a press apparatus suitable for pressurising a capsule to at least one gigapascal (GPa), the press apparatus comprising a frame suitable for accommodating the capsule and at least four load devices (four or six, for example), each load device securable in relation to the frame and capable of applying variable load onto the capsule by urging a respective anvil against the capsule in response to control of an operating parameter; the method including locating the capsule against a respective bearing end surface of each of a first set of at most three anvils arranged to be capable of supporting the capsule against gravity; using a first displacement mechanism to move each of a second set of at least one anvil into an intermediate position, in which respective bearing end surfaces of each anvil of the second set is spaced apart from the capsule; using a second displacement mechanism to move each anvil of the second set into a respective initial position in contact with the capsule; measuring initial values of the operating parameter in respect of each of the anvils in the respective initial positions; and controlling the operating parameter in respect of each of the anvils, treating the set-point as being relative to the respective initial value.

In some examples, each load device may comprise a ram capable of reciprocating within a chamber of a hydraulic cylinder in response to hydraulic fluid being pumped into or from the chamber, and comprising an intensifier member capable of reciprocating within the chamber; configured such that the ram can be urged to reciprocate within the chamber in response to reciprocation of the intensifier member within the chamber when the chamber is filled with hydraulic fluid; the method including positioning each anvil to a respective starting position, such that it engages a respective side of the capsule with sufficiently low force to avoid substantial crushing of the capsule; in which the first displacement mechanism comprises pumping hydraulic fluid into or from the hydraulic cylinder.

In some examples, the second displacement mechanism comprises reciprocation of the intensifier member.

Some example methods may include disengaging the second displacement mechanism when then pressure in the hydraulic fluid increases as a result of contact between the anvil and the capsule. Viewed from a third aspect, there is provided a press apparatus suitable for pressurising a capsule to at least one gigapascal (GPa), comprising a frame suitable for accommodating the capsule and at least four load devices, each securable in relation to the frame and capable of applying variable load onto the capsule by urging a respective anvil against the capsule in response to control of a first or a second variable operating parameter; measurement mechanisms for measuring the values of first and second operating parameters in respect of each of the load devices; and a control mechanism for controlling each load device according to a set-point for the first or the second operating parameter.

In some examples, a press apparatus may comprise a ram capable of reciprocating within a chamber of an hydraulic cylinder in response to hydraulic fluid being pumped into or from the chamber, and comprising an intensifier member capable of reciprocating within the chamber; configured such that the ram can be urged to reciprocate within the chamber in response to reciprocation of the intensifier member within the chamber when the chamber is filled with hydraulic fluid; and configured such that the ram can be urged to reciprocate within the chamber in response to pumping of hydraulic fluid into or from the chamber. BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting example arrangements will be described with reference to the accompanying drawings, of which

Fig. 1A shows a schematic drawing of an example cubic press apparatus for generating ultra-high pressures, assembled as in use;

Fig. 1 B shows a schematically partly cut-away side view of the example press apparatus shown in Fig. 1A, including two example hydraulic load generation cartridges;

Fig. 1 C shows a schematic cross-section view of an example hydraulic load generation cartridge shown in Fig. 1A and Fig. 1 B;

Fig. 2 shows a schematic cross section view of part of an example hydraulic load generation cartridge;

Fig. 3 shows a schematic example control diagram for a load generation device on the basis of pressure set-point; Fig. 4 shows a schematic example control diagram for a load generation device on the basis of ram displacement set-point;

Fig. 5 shows an example schematic control diagram for four load generation devices of a tetrahedral press system;

Fig. 6 shows an example schematic hybrid control diagram for six load generation devices of a cubic press system; and

Fig. 7 shows an example schematic hybrid control diagram for six load generation devices of a cubic press system. DETAILED DESCRIPTION

With reference to Fig. 1A, Fig 1 B and Fig. 1 C, an example cubic press apparatus 200 comprises a unitary steel frame 300 having six sides, each side provided with a bore hole 310 for accommodating a respective load device comprising a hydraulic cartridge 100 (which may be referred to simply as a 'cartridge'). The frame 300 has a central chamber for housing a capsule 400 to be pressurised. In Fig. 1A, each of six cartridges 100 is mechanically fastened to the frame 300 by axial 142 and radial fastening mechanisms, so that the cartridge 100 is prevented from substantial axial movement within the respective bore hole 310 and from substantial polar or azimuthal movement relative to the centre of the capsule 400. In the example illustrated in Fig. 1 C, each cartridge 100 comprises a hydraulic cylinder 140 (which may be referred to simply as a 'cylinder') configured to be attachable to the frame 300, a ram 120 that can reciprocate within a chamber 150 filled with hydraulic fluid, and an intensifier rod 190 that can also reciprocate within the chamber 150. An anvil 124 may be mounted onto an anvil holder 122 coupled to the ram 120, configured such that the anvil 124 will be urged outward (away from the hydraulic chamber 150) in response to hydraulic fluid being pumped into the chamber 150 or the intensifier rod 190 being driven into the chamber 150. The anvil 124 may comprise cemented tungsten carbide and be suitable for engaging and pressurising a capsule 400 for the synthesis or sintering of synthetic diamond or cubic boron nitride (cBN) crystals.

In use, the intensifier rod 190 may be driven into the chamber 150 and withdrawn from the chamber 150 by an electro-mechanical drive mechanism 130, 132. The drive mechanism comprises a servo-motor 130 and threaded rods 132 coupled to the servomotor 130 such that they can be synchronously driven by the servo-motor 130 to rotate about their respective axes. The intensifier rod 190 is coupled to the threaded rods 132 such that the rotation of the threaded rods will result in movement of the intensifier rod 190 along the longitudinal axis L. When the intensifier rod 190 is driven a distance into the chamber 150, it will tend to compress hydraulic fluid in the chamber 150 with a force applied by the drive mechanism 130, 132, which will cause the pressure in the hydraulic fluid to increase if the ram 120 is not free to move unconstrained, such as when a capsule 400 is being pressurised. The ram 120 will thus be urged forward, towards the capsule 400 when the press apparatus 200 is in the assembled condition in use, according to the principles of hydraulic mechanics. Each of the six cartridges 100 may be energised to drive the respective anvils 124 onto the capsule 400 from each of six respective directions. Load will thus be applied onto the capsule 400 and onto the frame 300 (reaction force in the opposite direction) via the fastening mechanisms 142 between the frame 300 and the cartridges 100. The press apparatus 200 may be configured such that pressures of at least about 5 GPa, or at least 7 GPa can be generated within a capsule 400 as all six of the anvils 124 are driven against the capsule 400 by the respective hydraulic cartridges 100.

With reference to Fig. 2, an example cartridge 100 comprises a pressure transducer 160 arranged for measuring the pressure of hydraulic fluid contained within the chamber 150, and a displacement transducer 180 arranged for measuring displacement of the ram 120, connected to the ram 120 by a connecting rod 170.

Some press apparatuses 200 comprise a unitary frame 300 cast as a single component, in which each of the six cartridges 100 is rigidly secured to one of six sides of the unitary frame 300. However, other cubic systems comprise six separate segments coupled to each other by means of pins, allowing the segments to move somewhat relative to each other as the respective load generation devices attached to each segment are activated and the capsule is thus pressurised. The risk of nonuniform deformation of a capsule in such press systems will be greater than in unitary systems, since the frame itself will likely be a source of non-uniformity.

Examples of cubic press assemblies are disclosed in European patent application publication number 2 830 869 and examples of hydraulic load devices are disclosed in European patent application publication number 2 830 867. In an example ultra-high pressurisation cycle applied to a cubic capsule 400 in a cubic press apparatus 200. Each of the cartridges 100 may comprise a ram 120 and configured such that the ram 120 can be driven towards the capsule 400 during the cycle when the cartridge 100 is secured to the frame 300. An anvil 124 may be coupled to the ram 120 such that the anvil 124 can be driven to engage the capsule 400 in response to movement of the ram 120, thus applying load onto the capsule 400.

Moving the six anvils 124 of a cubic press apparatus 200 into initial positions in which they just contact the respective six sides of the capsule 400 may be carried out in two stages. In order to load the capsule 400 into position in a cubic press apparatus 200, a first set of three adjacent anvils coupled to orthogonally oriented cartridges may initially be positioned into respective initial positions such they can support the capsule 400. Three capsule sides forming a corner of a cube may be thus supported by the anvils (the anvils will likely include at least one lower-most anvil so that the capsule can rest gravitationally on the lower-most anvil). The required initial positions of the first set of anvils may be established in a previous process, which may include loading a calibration block into the press apparatus 200. For example, the calibration block may consist of aluminium and have outer dimensions and configuration substantially the same as the capsule 400 to be loaded.

Once the anvils of the first set have been set in their initial position and the capsule 400 placed against them, the other three anvils (forming a diametrically opposite corner of a cube) may be moved into their initial positions. In some examples, this may be achieved by retracting the respective rams 120 of the respective cartridges 100 and using respective adjustable mechanical limit mechanisms, such as nuts, for limiting the movement of each anvil 124 so that it can be set into the desired position against the limit mechanism.

In some examples, each of the second set of anvils 124 may be put into its initial position in two steps, in which the anvils 124 are moved close to the capsule 400 relatively quickly, followed by more careful positioning against the capsule 400. In the first step, the anvil 124 may be moved into an intermediate position in response to hydraulic fluid being pumped relatively quickly into the cartridge 100 by a pump, the intermediate position being such that the end surface of the anvil 124 (which may be referred to as the 'face' of the anvil 124) is spaced apart from the respective side of the capsule 400 by about 0.2 to about 2 mm, depending on factors such as whether poor location of the capsule 400 is suspected and the dimensional and position tolerances of components of the press assembly. The pump used in this step may be relatively small and may be referred to as a 'fast-approach' pump, since the hydraulic fluid will not be substantially pressurised. In some examples, the gap may be about 0.5 mm, and in some examples each anvil 124 may be displaced in the first step at a rate of about 5 to about 10 mm per second. The end of the first step may be signalled by means of a limit switch or by measurement of the displacement of the anvil 124 (or ram 120) from a starting position. In the second step, each of the anvils 124 may be moved substantially more slowly to contact the respective side of the capsule 400, with sufficiently low force that the capsule 400 is not substantially crushed or damaged in some other way. In some examples, the fast-approach pump may be disengaged and movement of the anvil 124 achieved by means of an intensifier piston 190. Each anvil 124 may be advanced towards the capsule 400 until it contacts the capsule 400, which may be indicated by an increase in the pressure of the hydraulic fluid. This increase should be relatively small, for example about 5 bar. When the pressure of the hydraulic fluid is observed to increase owing to the contact, the anvil 124 is regarded as being in its initial position and further displacement avoided. Each of the anvils 124 may be positioned thus in sequence or simultaneously.

Once all six anvils 124 have been set in their initial positions for the pressurisation cycle, the displacement 180 and pressure 160 transducers may be in effect set at zero in control software, in that the anvils 124 are considered to be in the starting configuration from which subsequent loading and displacement are referenced. In other words, subsequent net anvil 124 displacement may be calculated by subtracting the initial displacement value from subsequently measured displacement. Similarly, the pressure of the hydraulic fluid in the cartridges 100 when the anvils 124 are in their initial positions may be regarded as base pressures, and subsequent effective pressures determined by subtracting the base pressure from pressure measured by the pressure transducers 160.

With reference to Fig. 3, a pressure control flow diagram for controlling a single load generation cartridge 100 based on a set-point hydraulic pressure XLP includes receiving the set-point pressure XLP as input to a controller unit C, which converts the input to electrical output to drive a motor M of an intensifier piston 190 of a load generation cartridge 1 00, in response to which the output pressure XOP of the hydraulic fluid in the chamber 150 changes (if movement of the ram 120 is constrained). The actual pressure XOP of the hydraulic fluid will be measured by a pressure transducer 1 60, PT and compared to the set-point pressure XLP, this comparison being the basis for controlling the drive motor M of the intensifier piston 190. The controller unit C will tend to minimise this difference according to a control algorithm so that the pressure XOP of the hydraulic fluid will be as close as possible to the set-point pressure XLP. For example, if the pressure XOP as measured by the pressure transducer 160, PT is less than the set-point pressure XLP, then the controller unit C will drive the motor M of the intensifier rod 1 90 to increase the pressure XOP of the fluid. Similarly, if the pressure XOP as measured by the pressure transducer 160, PT is greater than the set-point pressure XLP, then the controller unit C will drive the motor M of the intensifier rod 1 90 to decrease the pressure XOP of the fluid. The set-point pressure XLP will likely vary with time, for example increasing from ambient pressure to a target value at one or more rates, remaining constant for a period and then decreasing at one or more rates back to ambient pressure.

With reference to Fig. 4, a displacement control flow diagram for controlling a single load generation cartridge 100 based on a set-point displacement XLD of the ram 120 includes receiving the set-point displacement XLD as input to a controller unit C, which converts the input to electrical output to drive a motor M of an intensifier rod 190 of a load generation cartridge 1 00, in response to which the pressure of the hydraulic fluid in the chamber 150 will change such that the ram 120 will move to achieve the targeted displacement. The actual displacement XOD of the ram 120 will be measured by a displacement transducer 1 80, DT and compared to the set-point displacement XLD, this comparison being the basis for controlling the drive motor M of the intensifier rod 1 90. The controller unit C will tend to minimise this difference so that the displacement XOD of the ram 120 will be as close as possible to the set-point displacement XLD. For example, if the displacement XOD as measured by the displacement transducer 1 80, DT is less than the set-point displacement XLD, then the controller unit C will drive the motor M of the intensifier rod 190 to increase the pressure of the fluid and consequently to drive the ram 120 outwards. Similarly, if the displacement XOD as measured by the displacement transducer 180, DT is greater than the set-point displacement XLD, then the controller unit C will drive the motor M of the intensifier rod 1 90 to decrease the pressure of the fluid and retract the ram 120. The set-point displacement XLD will likely vary with time, for example increasing to a target value at one or more rates, and then potentially increasing with time to take into account endo- volumetric phase changes in the material of which a pressurised capsule 400 is comprised, or the conversion of graphite to diamond at an ultra-high pressure, and then decreasing at one or more rates back to a value at which the ram 120 will be fully retracted so that the capsule 400 can be recovered.

With reference to Fig. 5, an example control system comprises four separate pressure control systems, each for four separate hydraulic cartridges 100, driving four separate anvils 124 for impinging on a capsule 400 subject to a single set-point pressure XLP. Each of the four pressure control systems receives the same set-point XLP pressure and each controller unit C1 , C2, C3, C4 drives the respective motor M1 , M2, M3, M4 of the respective intensifier piston 190 to achieve the respective output pressure X1 OP, X2OP, X3OP, X4OP of the hydraulic fluid. The actual pressure of the hydraulic fluid in each of the four cartridges 100 is measured by the respective pressure transducer PT1 , PT2, PT3, PT4 and fed back into the respective control system to be compared to the common set-point pressure XLP, SO that each pressure control system can adjust its output pressure X1OP, X2OP, X3OP, X4OP to minimise the difference between the respective PT1 , PT2, PT3, PT4 value and the set-point pressure XLP. Thus each anvil 124 impinging from a different direction on a capsule 400 will tend to be driven according to the pressuring the hydraulic fluid of its corresponding hydraulic cartridge 100.

A potential difficulty with the approach described above with reference to Fig. 5 is that the capsule 400 may not be deformed in a way that corresponds exactly to the displacement of the anvils 124. For example, if the dimensions of the capsule 400 do not change by the same amounts in all four directions, then different cartridges 100 will exhibit the same hydraulic fluid pressure while the respective displacements of the ram 120 and anvil 124 will be different. If the differences between the displacements are greater than a critical value, there may be a substantial risk of a catastrophic sudden loss of pressure in the capsule (which may be referred to as a 'blow out') as material explosively escapes from the confinement of the capsule 400. In addition, if the frame 300 lacks rigidity then different parts of it may deform differently, potentially resulting in a similar lack of uniformity of pressure generation in the capsule 400 and anvil 124 displacement. With reference to Fig. 6, in an example hybrid control system for a cubic press apparatus 200 comprising six respective hydraulic cartridges 100, one of which will be selected as the master and the others will be slaves, in which six anvils 124 impinge on a capsule 400. In this example, the first (top) cartridge is the master and will be controlled on the basis of a set-point pressure X1 I_P, as described with reference to Fig. 3. However, the five slave cartridges will be controlled on the basis of the sampled displacement DT1 of the ram of the master device, so that DT1 will have the effect of the common set-point displacement XLP for all the slave devices. In this example, each slave device will be controlled as described with reference to Fig. 5, in which each will generate a displacement output X2OD, X3OD, X3OD, X4OD, X5OD according the difference between the actual displacement XOD of the respective ram and the set-point displacement XLD (DT1 ) received from the master device. In this way, the pressurisation of the capsule 400 will be controlled on the overall basis of the set-point pressure X1 I_P, and having regard to the deformation of the capsule 400 in response to this control, to reduce the risk that the differences in the displacements of the anvils 124 will not become too great. If the differences in pressure of the hydraulic fluid in the cartridges 100 exceeds a critical value, the pressurisation process can be aborted. Abort limits can be set in order to avoid unequal closure of the anvils, which can result in instability in use and potentially risk a 'blow out', in which material explosively escapes from the capsule, resulting in sudden loss of pressure and potential damage to the press apparatus. With reference to Fig. 7, in an example hybrid control system for a cubic press apparatus 200, in which one of the cartridges 100 will be selected as the master and the others will be slaves. This control system will operate similarly to that described with reference to Fig. 5, except that the master device will be controlled based on a displacement set-point X1 LD, and the slaves will be controlled based on the sampled value of the pressure PT1 of the hydraulic fluid of the master device (i.e. pressure and displacement are interchanged mutatis mutandis).

Although the examples described with reference to Fig. 6 and Fig. 7 involve six cartridges as in a cubic press system, they would apply mutatis mutandis to a system comprising four cartridges, as in a tetrahedral press system. An aspect of disclosed example methods of locating the anvils in their initial positions may be that different initial readings among transducers owing to differences in tolerance of mechanical components of the capsule or the cartridges, for example, can be negated. Thus, the performance of press assemblies and capsules having relatively poor dimensional and configuration precision (tolerance) may be enhanced by using an example displacement mechanism. The positions of the anvils and the transducer readings may be said to be calibrated according to the specific dimensions and arrangement of the capsule, cartridge and other components. This may be particularly important for using the pressurisation assembly and method for ultra-high pressure crystallisation processes, such as for synthetic diamond and cBN crystals, as well as sintering processes, such as the sintering of cBN grains and binder material to produce polycrystalline cBN (PCBN) material. A pressurisation cycle selected according to the desired process, such as diamond or cBN crystallisation or sintering, can then be applied on the basis of the anvils being at a 'zero' starting position, in which the anvils will be driven by the respective hydraulic cartridges towards the capsule to apply load onto the capsule, this displacement being measured as positive displacement of the anvils in relation to the respective cartridge cylinder as attached to the frame, each anvil being thus extended further in relation to the cylinder. If all anvils move by exactly the same distance from the zeroed starting position, then the transducers would indicate the same displacement for all anvils. Any of various control methods may be used to control the pressurisation cycle, including control on the basis of an anvil displacement set-point curve, an anvil loading or hydraulic fluid pressure set-point curve or a combination of anvil displacement and loading set-points, as disclosed herein.

Certain terms and concepts as used herein will be briefly explained. Unless otherwise stated, measurement and / or control of an operating parameter shall herein refer specifically to that parameter or to any other parameter from which the operating parameter referred to can be derived or calculated in principle. So, for example, displacement of a ram of a hydraulic cartridge may be equivalent for this purpose to the displacement of an anvil directly or indirectly coupled to the ram such that the displacement of the one can be derived in principle from knowledge of the displacement of the other. As another example, the pressure of hydraulic fluid comprised in a cartridge and capable of driving the movement of a ram may be equivalent for this purpose to a parameter directly associated with pressurising the hydraulic fluid, provided that the pressure of the hydraulic fluid can be derived in principle from that parameter.

As used herein, hydraulic fluid is a fluid medium by which power can be transferred in hydraulic machinery. Examples of hydraulic fluids include fluids based on mineral oil or water.

As used herein, ultra-high pressure shall mean a pressure of at least 1 GPa.

As used herein, a transducer is a device that converts a signal in one form of energy to another form of energy, in which examples of energy types include electrical, mechanical, electromagnetic, chemical, acoustic and thermal energy. Transducers are widely used in measuring instruments.

As used herein, a control system is a device or assembly of devices capable of controlling or regulating the behaviour of another device or assembly, such as machines, pressurisation apparatus, hydraulic systems, for example. The output of an open loop control system is generated based on inputs. In closed loop control systems (which may be referred to as a feedback control system), the current output is taken into consideration and corrections are made based on feedback. An automatic sequential control system may trigger a series of mechanical actuators in the correct sequence to perform a task. In a linear feedback system, a control loop including sensors, control algorithms and actuators, is arranged such that a variable parameter can be regulated according to a set-point value. A system to be controlled my comprise a sensor for measuring a parameter to be controlled as well as a device for altering that parameter, and a control system may continually or intermittently compare the measured parameter value and compare it to a set-point value, and actuate the device so as to minimise this difference over time, or try to maintain the difference within an acceptable range to the extent possible.