ROTARY TABLET PRESS WITH TABLET OUTLET, TABLET OUTLET FOR SAID ROTARY TABLET PRESS AND METHOD FOR PRODUCING TABLETS ON A TABLET PRESS

Abstract

A rotary tablet press, having a rotor, which is driveable about a vertical axis of rotation and has a die plate with die bores for producing tablets inside the die bores by means of punch pairs, having at least one filling station, having at least one pressing station, and having at least one tablet outlet for removing the produced tablets out of the rotary tablet press, with which is associated a discharging device, by way of which tablets, in dependence on a control signal, can be supplied as single tablets to a first channel or as a tablet stream to a second channel in the tablet outlet. In order to enable increased production output with improved adherence to the demands on the tablets, a weighing device with a weighing cell is incorporated into the tablet outlet, tablets from the first channel being suppliable to the weighing device by means of a supply channel.

Claims

1-22. (canceled)

23. A rotary tablet press, having a rotor, which is driveable about a vertical axis of rotation and has a die plate with die bores for producing associated tablets inside the die bores by way of punch pairs, having at least one filling station for supplying pressing material for the associated tablets, having at least one pressing station for applying a pressing force onto the punches of the punch pairs, and having at least one tablet outlet for removing associated produced tablets out of the rotary tablet press, with which tablet outlet is associated a discharging device, by way of which, in dependence on a control signal, associated tablets being suppliable as single tablets to a first channel or as a tablet stream to a second channel in the tablet outlet, a weighing device with a weighing cell is incorporated into the tablet outlet, associated tablets from the first channel being suppliable to the weighing device by way of a supply channel.

24. The tablet press according to claim 23, further including a pressing force measuring apparatus in the pressing station and an evaluating and control device, by way of which a control signal for the discharging device is generatable in dependence on the measuring signal of the pressing force measuring apparatus, wherein the discharging device is controllable via the evaluating and control device for singling-out associated test tablets to be supplied to the weighing device and the punch pairs used to press the associated tablets discharged into the supply channel to the weighing device is storable in the memory of the evaluating and control device.

25. The tablet press according to claim 23, wherein an adjustable separator is assigned to the first channel, wherein associated tablets in the first channel are only supplied to the supply channel in one position of the separator.

26. The tablet press according to claim 23, wherein the tablet outlet has a first outlet channel for associated good tablets and a second outlet channel for associated bad tablets, wherein a third outlet channel is preferably provided for associated sample tablets.

27. The tablet press according to claim 23, wherein the tablet outlet has a first plane and at least one second, upper plane, wherein the supply channel to the weighing device is situated in the upper plane.

28. The tablet press according to claim 25, wherein the separator is formed by a height-adjustable flap.

29. The tablet press according to claim 23, wherein the weighing device has a good outlet for associated good tablets and a separate bad outlet for associated bad tablets.

30. The tablet press according to claim 29, wherein the good outlet of the weighing device opens out into an outlet channel for the associated good tablets.

31. The tablet press according to claim 23, wherein several weighing devices are incorporated into the tablet outlet, separators or a sorting device are provided for each of the several weighing device.

32. The tablet press according to claim 23, wherein the weighing device, inside a framework fastened to the tablet outlet, has a weighing chamber with a chamber bottom coupled to the weighing cell, with a first side wall which is closable by way of a movable wall flap, the wall opening of which opens into the good channel, and with a second side wall which is closed by way of a movable wall flap, the wall opening of which opens into the bad channel.

33. A tablet outlet for a rotary tablet press having a rotor, which is driveable about a vertical axis of rotation and has a die plate with die bores for producing associated tablets inside the die bores by way of punch pairs, having at least one filling station for supplying pressing material for the associated tablets, having at least one pressing station for applying a pressing force onto the punches of the punch pairs, and having at least one tablet outlet for removing associated produced tablets out of the rotary tablet press, with which tablet outlet is associated a discharging device, by way of which, in dependence on a control signal, associated tablets being suppliable as single tablets to a first channel or as a tablet stream to a second channel in the tablet outlet, a weighing device with a weighing cell is incorporated into the tablet outlet, associated tablets from the first channel being suppliable to the weighing device by way of a supply channel, the tablet outlet having at least one first channel and one second channel which, in dependence on a control signal to a discharging device of the rotary tablet press, is actable upon with tablets individually or as a tablet stream, that the tablet outlet further including a weighing device with a weighing cell, to which associated tablets from the first channel are suppliable via a supply channel, is incorporated into the tablet outlet.

34. The tablet outlet according to claim 33, wherein an adjustable separator is assigned to the first channel, wherein associated tablets in the first channel are only supplied to the supply channel in one position of the separator.

35. The tablet outlet according to claim 33, having a first outlet channel for associated good tablets and a second outlet channel for associated bad tablets, wherein a third outlet channel is preferably provided for associated sample tablets.

36. The tablet outlet according to claim 33, wherein the tablet outlet has a first plane and at least one second, upper plane, wherein the supply channel to the weighing device is situated in the upper plane.

37. The tablet outlet according to claim 34, wherein the separator is formed by a height-adjustable flap.

38. The tablet outlet according to claim 33, wherein the weighing device has a good outlet for associated good tablets and a separate bad outlet for associated bad tablets.

39. The tablet outlet according to claim 38, wherein the good outlet of the weighing device opens out into an outlet channel for the associated good tablets.

40. The tablet outlet according to claim 33, wherein several weighing devices are incorporated into the tablet outlet, separators or a sorting device are provided for each of the several weighing device.

41. The tablet outlet according to claim 33, wherein the weighing device, inside a framework fastened to the tablet outlet, has a weighing chamber with a chamber bottom coupled to the weighing cell, with a first side wall which is closable by way of a movable wall flap, the wall opening of which opens into the good channel, and with a second side wall which is closed by way of a movable wall flap, the wall opening of which opens into the bad channel.

42. A weighing device for a rotary tablet press having a rotor, which is driveable about a vertical axis of rotation and has a die plate with die bores for producing associated tablets inside the die bores by way of punch pairs, having at least one filling station for supplying pressing material for the associated tablets, having at least one pressing station for applying a pressing force onto the punches of the punch pairs, and having at least one tablet outlet for removing associated produced tablets out of the rotary tablet press, with which tablet outlet is associated a discharging device, by way of which, in dependence on a control signal, associated tablets being suppliable as single tablets to a first channel or as a tablet stream to a second channel in the tablet outlet, a weighing device with a weighing cell is incorporated into the tablet outlet, associated tablets from the first channel being suppliable to the weighing device by way of a supply channel, the weighing device having a framework, having a weighing chamber arranged inside the framework with a chamber bottom coupled to a weighing cell, with a first side wall and with a second side wall, the framework is fastenable to the tablet outlet of an associated rotary tablet press, wherein a wall opening which is closable by way of a movable wall flap is provided in the first side wall and a wall opening which is closable by way of a movable wall flap is provided in the second side wall in order to supply associated tablets after weighing to a bad channel for associated bad tablets or to a good channel for associated good tablets.

43. The weighing device according to claim 42, wherein the wall flaps are rotatably mounted close to their top flap end and are loaded in the closed position by way of the force of gravity.

44. The weighing device according to claim 42, wherein air conduction channels are realized in at least one of the framework and the side walls for pneumatic movement of an associated tablet and/pneumatic actuation of the wall flaps by way of a compressed air system.

45. The weighing device according to claim 43, wherein the wall flaps have an actuating projection above the pivot bearing, it being possible for the actuating projections to be acted upon with compressed air in opposition to their closing direction via outlet nozzles of the compressed air system.

46. The weighing device according to claim 45, wherein in the framework a first locking device is provided for the first wall flap and a second locking device is provided for the second wall flap, wherein the outlet nozzle is coupled to the locking device for the second wall flap for opening the first wall flap and the outlet nozzle is coupled to the locking device for the first wall flap for opening the second wall flap.

47. The weighing device according to claim 42, wherein the measuring chamber has a third side wall opposite the first side wall and a fourth side wall opposite the second side wall, wherein ejection nozzles are arranged in the third and fourth side walls, by way of the ejection nozzles associated tablets being suppliable in a selectable manner from the chamber bottom to the good channel or to the bad channel, wherein preferably in each case one ejection nozzle is coupled to the associated outlet nozzle in the opposite side wall.

48. A method for producing tablets on a rotary tablet press which has a rotor which is driveable about a vertical axis of rotation and includes a die plate with die bores, in which tablets are produced by way of punch pairs, the at least one filling station in which pressing material for the tablets is supplied to the die bores, the at least one pressing station in which a pressing force is applied to the punches of the punch pairs, the at least one tablet outlet, with which a discharging device is associated, by way of which tablets, in dependence on a control signal, are supplied as single tablets to a first channel or as a tablet stream to a second channel in the tablet outlet, and the one evaluating and control device by way of which a control signal is generated for the discharging device and automatic control of process parameters of the tablet press is effected, incorporating a weighing device into the tablet outlet, supplying weighing device tablets from the first channel via a supply channel, considering the measuring signal of the weighing device as a process parameter in the automatic control.

49. The method according to claim 48, wherein the punch pairs which are used to produce the tablets, the weight of which is measured by way of the weighing device, is recorded in the evaluating and control device together with the force due to weight during the pressing operation in the pressing station.

50. The method according to claim 48, wherein a mean value, which is used for automatic control of the tablet press, is formed from multiple measuring signals of the weighing device.

51. The method according to claim 48, wherein at least 1 tablet is supplied to the weighing device at least as frequently as every two rotations of the rotor.

52. The method according to claim 48, wherein tablets which have been produced with different punch pairs are measured in two consecutive measurements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail and illustrated in the accompanying drawings which form a part hereof and wherein:

[0021] FIG. 1 shows a schematic top view of a rotary tablet press with a tablet outlet according to the invention connected and an evaluating device indicated;

[0022] FIG. 2 shows a top view of a detail of the tablet outlet with the cover removed;

[0023] FIG. 3 shows a perspective view of a tablet outlet according to the invention;

[0024] FIG. 4 shows a perspective view of the tablet outlet from FIG. 3, when looking onto the entry side; and

[0025] FIG. 5 shows a schematic representation of the design of a metering device for the tablet outlet according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] Referring now to the drawings wherein the showings are for the purpose of illustrating preferred and alternative embodiments of the invention only and not for the purpose of limiting the same, FIG. 1 shows a very simplified schematic representation of a rotary tablet press given the overall reference of 1. In a known manner per se, the tablet press 1 has a housing case 2 with fixed, openable access walls and a rotor 3 is rotatably mounted inside the housing 2, of which only the die plate 4 with a plurality of die bores 5 arranged offset around the circumference on a pitch circle is shown in the drawing. Individual tablets, here round tablets, can be produced in large quantities inside the die bores 5, by means of a punch pair (not shown), one of which forms an upper punch and the other a lower punch, which rotate together with the rotor 3 and are raised or lowered by means of guide cams, as is known per se to the expert for rotary tablet presses. The material is supplied into the individual die bores 5 inside a filling station 6, shown in a schematic manner by means of a filling shoe 7, and once the die bores 5 have been filled and, where applicable, metering has taken place inside a metering device (not shown), the material is compressed by means of a first pressing station 8, in which a preliminary pressure is applied, and in a second pressing station 9, in which the main pressure is applied. In the exemplary embodiment shown, only the pressing station 9 has associated therewith a schematically indicated pressing force measuring apparatus 11, by way of which the pressing pressure of the associated punch pair is measured in the pressing station 9 and can be supplied to a control and evaluating device 50 as a measuring signal via a suitable signal line 12.

[0027] The rotary tablet press 1, in addition, is provided in a manner known per se with a discharging device 13, which, on the one hand, has a removal rail 14 in order to be able to supply the tablets 10 produced inside the die bores 5 as a tablet stream, as shown, to a multiplechannel tablet outlet 20, and which, on the other hand, has a preferably pneumatically operated singling-out apparatus 15 as a component of the discharging device 13, by means of which individual tablets, like the sample or test tablets 10 shown schematically in FIG. 1, can be supplied as single tablets to another channel of the tablet outlet 20. The control of the discharging device 13 or of the singling-out device 15 inside the discharging device 13 is effected by means of a control signal from the evaluating and control device 50 and an associated control module 16 for the compressed air supply to the singling-out device 15. A rotary tablet press 1 with the aforementioned design is sufficiently known to the relevant expert, which is why no detailed description is effected here.

[0028] In the case of the rotary tablet press 1 according to the invention, a weighing device 40 with a suitable measuring cell for direct weighing a tablet is incorporated into the tablet outlet 20, and the measuring signal of the weighing cell of the weighing device 40 can be supplied via a further signal line 17 to the evaluating and control device 50. Separators, sorting devices and/or ejection nozzles can be actuated via the signal line 18 inside the tablet outlet 20 and/or the weighing device 40 by means of the evaluating and control device 50, as will be explained below with reference to FIGS. 2 to 5.

[0029] FIG. 2 shows the tablet outlet 20 with the cover removed. A cover is necessary in particular when a tablet press is used to produce pharmaceutical tablets where there are relatively strict requirements and contaminants produced by the ambient air and other influences have to be avoided. On its entry side, which in the mounted state of the tablet outlet 20 faces the discharging device 13, the tablet outlet 20 has a first channel 21 for those tablets 10 which have been sorted out from the produced tablets 10 as single tablets by means of the singling-out device 15, and it has a second channel 22, by means of which tablets 10 can be guided out of the tablet press as a tablet stream. In normal operation, the individual tablets 10 would normally lie edge to edge in the product stream.

[0030] On the exit side, the tablet outlet 20 in the exemplary embodiment shown has a first outlet channel 23 for good tablets, a second outlet channel 24 arranged here in the center for bad tablets and a third outlet channel 25, by means of which tablets singled-out in the first channel 21 can be selectively supplied to an external sample test. A sorting flap 26, which in the representation according to FIG. 2, would still supply the tablet stream of tablets 10 to the bad channel 24 is associated with the tablet outlet 20 inside the second channel 22; during production, in particular when the tablet press has completely started-up, the sorting flap 26 is pivoted in such a manner that its exit end opens out into the good channel 23. To this end, the sorting flap 26 can be activated, for example, in a mechanical, electro-mechanical or pneumatic manner. In the state attached to a tablet press 1, the bottom 27 of the tablet outlet 20 normally lies in an inclined manner and forms a chute, so that the individual tablets slide into the outlet channels 23, 24 or 25 through the force of gravity.

[0031] The first channel 21, into which the tablets 10 are fed by means of the singling-out device 15, has associated therewith a supply channel 28, by means of which the singled-out tablets are supplied to the weighing machine 40. It can be seen relatively well from FIGS. 2 to 4 that the supply channel 28 is located at a higher level than the bottom plate 27 of the tablet outlet 20 and, in particular, is located at a higher level than the associated line channels 23A, 24A, 25A for the individual tablet outlets 23, 24, 25 inside the tablet outlet 20, which are defined below by the bottom plate 27. The supply channel 28 and the weighing device 40, therefore, form inside the tablet outlet 20 a second upper plane, which is located at a higher level than the bottom plane with the channels 21, 22 or the line channels 23A, 24A and 25A, which is defined by the bottom plate 27. Whether or not a tablet 10, which is discharged into the first channel 21 in a singled-out manner by means of the singling-out device 15, is supplied to the supply channel 28 or the sample channel 25, is preset by means of the evaluating and control device (50, FIG. 1), which, for this purpose, can control adjustable separator 29, which are associated with the first channel 21 on the entry side. In the exemplary embodiment shown, the separator 29 essentially consist of a height-adjustable pivot flap 30, which is rotatably mounted on one side and which can be seen in a particularly clear manner in FIG. 4 in its upper pivot position in which nothing is supplied to the supply channel 28. The actuation of the flap 30 can be effected, in particular, in a pneumatic manner by means of a pneumatic drive 31, which is attached to the tablet outlet 20. The suspension of the pivot flap 30, which is pivotable about a horizontal pivot axis, is effected by means of two bearing blocks 32, which are fastened on both sides of the pivot flap 30 approximately at the level of the bottom of the upper second plane on the tablet outlet 20 or on a tablet outlet housing. If the flap 30 is in the bottom position (not shown), the tablet 10 is moved by means of the ejection pulse of the discharging device 15 along the ramp formed by way of the pivot flap 30 upwards into the higher plane and then passes by means of the tubular supply channel 28 into a weighing chamber 41 of the weighing device 40. The weighing chamber 41, in this case, has a rectangular design with four side walls and it is open upwards such that the tablets can be poured from above into the weighing chamber 41. If a tablet to be weighed is located inside the weighing chamber 41, a measurement is effected and the measuring signal of the weight measurement is sent back to the evaluation and control device and is logged there. At the same time, the punch pair, by way of which the tablets, singled-out by means of the discharging device 15 and measured in the weighing chamber 41 of the weighing device 40, have been produced, is logged in the evaluating and control device 50. Precise association is only possible when a tablet, singled-out into the first channel 21 of the tablet outlet 20, is supplied to the weighing device 40, wherein, in addition, in dependence on the rotational speed of the rotor, it can also be necessary for a certain number of tablets to have to be supplied to the second channel 22 before and after the singled-out tablets, as otherwise the time available would not be enough to move the separator 29 into the position in which the tablet is supplied as a single tablet to the supply channel 28.

[0032] As can be seen particularly clearly in FIGS. 2 and 3, tablets can be supplied from the weighing chamber 41 in a selective manner by means of a good outlet 43, which is formed, for example, by a curved chute, to the tablet outlet 23 for good tablets or by means of a bad outlet 44, which is once again formed by a curved chute, to the tablet outlet 24 for bad tablets without leaving the tablet outlet 20, that is to say still inside the tablet outlet 20. As a rule, the tablets supplied to the weighing device 40 are those where the pressing force measuring apparatus has, in any case, determined a value that lies within the tolerance limits for the pressing force, and in such a case the measurement inside the weighing device 40 forms a control measurement for the precise weight determination and optimization of the process parameters for the tablet press, which is why, when the overall weight is maintained, the tablet can be supplied without any problem to the good stream inside the tablet outlet 23 for good tablets. The tablet supplied by means of the supply 28 to the weighing device 40 for weighing, however, can also be such a tablet 10 which has been ejected by means of the discharging device 15 because the pressing force was outside the tolerance range. The weight of the tablet can be checked via the weighing device 40, and if, in spite of the error message on account of the pressing force measuring sensor, the weight lies within a predetermined tolerance range, the decision can be made with regard to discharging out of the weighing device 40 to supply the tablet, nonetheless, by means of the good channel 43 to the tablet outlet 23 for good tablets. If the weight is confirmed to be too low, the discharging out of the weighing device 40 is effected into the bad channel 44 and subsequently into the outlet 24 for bad tablets. The check is still effected inside the tablet outlet 20 as close as possible to the tablet press, and as for the tablet outlet 20 clean room conditions, as in the press room, also have to be maintained for pharmaceutical products, a tablet measured with regard to its weight can still be supplied to the product stream for the production output.

[0033] FIG. 5 now shows a particularly advantageous design of a weighing device 40. The weighing device 40 has a framework 45, by way of which it is fastened, for example, to the bottom 27 of the tablet outlet 20 between the line channels 23A, 24A in such a manner that the actual weighing chamber 41 is located higher than the bottom plate 27 at the necessary spacing. The bottom of the weighing chamber 41 consists of, in this case, a plate-shaped tablet tray 66, which is coupled in a suitable manner via a plunger or directly to a weighing cell (not shown) which determines the weight of a tablet placed on the tablet tray 46 and forwards it to the evaluating and control device (50, FIG. 1). In the case of a rectangular or, in this case, quadratic design of the weighing chamber 41, said chamber has a first side wall 46, a second wall 47, a third side wall 48 which is opposite the first side wall 46 and a fourth side wall 48 which is opposite the second side wall 47. A first wall opening 46A is provided in the first side wall 46 and a second wall opening 47A is provided in the second side wall 47, by means of which measured tablets can be supplied either to the good outlet or the bad outlet. Both wall openings 46A, 47A are in each case closed by way of a separate wall flap 51, said wall flaps essentially being designed in an identical manner, FIG. 5 showing the wall flap 51 for the wall opening 46A in the closed position and that for the wall opening 47A being shown in the open position. Both wall flaps 51 are in each case mounted close to their upper end so as to be rotatable about an axis of rotation 52, a projection 53 being realized as an actuating projection on the wall flap 51 above the axis of rotation 52. The wall flaps 51 open outwards and the framework 45 is arranged together with the bearing axes 52 for the wall flaps 51 in such a manner that the wall flaps 51 remain in their closed position by means of the force of gravity.

[0034] In the case of the weighing device 40 shown, the opening of the wall flaps 51, and also the ejection of a tablet measured beforehand with regard to its weight, is effected by means of compressed air, which is distributed by means of a schematically indicated ventilation system in the framework 45, in particular in the side walls 46 to 49. The compressed air system with the ventilation channels in the framework 45 is constructed in such a manner that there are two separately controllable line branches, the one line branch including an outlet nozzle 54 which is associated with the actuating projection 53 on the ventilation flap 51 for the wall opening 46A, whilst the other line branch has an outlet nozzle 54 for the other wall flap 51 on the wall opening 47A. The control of the nozzle 54 is effected, for example, by means of the hose 57 and the control of the nozzle 55 is effected by means of the hose 58. In FIG. 5, the hose 58 is acted upon momentarily with compressed air, which is why the wall flap 51 in the side wall 47 is open. At the same time as the air exits at the nozzle 55, an ejection nozzle 59A is actuated, said ejection nozzle being realized in the second side wall 49 and being located opposite the wall opening 47A in such a manner that a tablet positioned on the tablet tray 66 is expelled through the wall opening 47A and, for example, is ejected into the good channel. At the same time, in order to make sure in a reliable manner that the wall flap 51 for the wall opening 46A does not open as a result of the compressed air differentials, the ventilation system is connected by means of a further channel inside the fourth side wall 49 to an outlet nozzle 60A which is situated on the outer surface or rear surface of the flap 51 for the wall opening 46A and prevents it being possible for the wall flap 51 of the wall opening 46A to be opened unintentionally through overpressure in the weighing chamber 41. A corresponding ventilation system is also connected in a mirror-symmetrical manner to the hose 57 such that whenever a tablet is to be transferred, for example, into the bad channel, the wall flap 51 for the wall opening 47A remains in its closed position and the wall flap 51 for the wall opening 46A, at the same time as the ejection nozzle 59 is actuated, is opened by means of the nozzle 54, whilst the nozzle 60 serves as a locking device for the other wall flap 51.

[0035] Tablets can be supplied to the weighing device 40 at certain time intervals, the minimum interval depending on the actuating times for the separator and the rotational speed of the rotor. A considerable improvement in the production process for tablets in particular produced from high-value initial materials can be achieved when at least one tablet is supplied to the weighing device per revolution or per two revolutions and, where applicable, a control parameter for the automatic control of the tablet press is derived from the measured weight. Through additional discharging devices, additional tablet outlets or additional weighing devices with associated separators, the number of tablets tested in normal operation, therefore continuously, can be increased and after successful measurement adhering to all the tolerance limits, can be once again supplied to the production output of good tablets. In place of the afore-described pneumatic actuation of the separators and flaps, it could also be possible for it to be effected in a mechanical or electro-mechanical manner; it could also be possible to combine pneumatic and mechanical actuation, particular advantages being provided, however, through entirely pneumatic control of the locking device, of the opening devices and of the ejection device out of the weighing device. As it is possible to store the weight actually present at the tablet together with the punch numbers of the punch pair and the measured pressing force, it is also possible to ascertain errors made here at individual punch pairs. It is true that a control parameter could be derived from each individual value, greater precision can be achieved, however, by mean values being formed from a certain number of individual measurements, for example from ten individual measurements, as required in the pharmaceutical industry, before a control parameter for the tablet press is derived. Automatically taring the weighing device at certain intervals in time can prevent the weighing device itself forming a source of error.

[0036] To the expert, numerous modifications which are to fall within the range of protection of the attached claims, proceed from the preceding description. In particular, the invention is not restricted to the exemplified embodiment shown. The exemplary embodiment explains the invention by way of a tablet press which creates a tablet when revolving about 360. For shorter production time, two tablet outlets, two or four pressing stations and in a corresponding manner two filling stations could be arranged on the tablet press. A sample sequence can also be omitted.

[0037] Further, while considerable emphasis has been placed on the preferred embodiments of the invention illustrated and described herein, it will be appreciated that other embodiments, and equivalences thereof, can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. Furthermore, the embodiments described above can be combined to form yet other embodiments of the invention of this application. Accordingly, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.