Tableting machines have been known for many years and one particular type thereof which has received a high level of development and is widely used comprises a rotary table containing die openings therein, together with means for introducing powder for tableting into such die openings, upper and lower punches for compressing such powder into tablets and means for ejecting the tablets from said openings.
There is, however, a continuing problem in the operation of such machines in that different formulations of powder have a wide range of varying physical characteristics which results in varying substantially the capacity of said powder to flow through the feeding mechanism, to be received into the die openings and to be compressed into tablets. Such variations if uncontrolled will lead to wide variations in the density, and consequently weight, of the finished tablets. Since the weights of such tablets to be acceptable must be held within a predetermined range and since any tablets out of this range are essentially a loss to the pharmaceutical company, it is obviously desirable to hold the variations in tablet weight to within such range.
A great amount of effort has gone into controlling the feeding of powders to the dies of a tableting machine and the machines now in commercial use have attained a high degree of sophistication. In some instances, automatic means have been provided for sensing the pressure developed in forming the tablets and adjusting the feed as needed to maintain the pressure within a specified range. For example, strain sensing equipment has been installed into a tableting machine for sensing the tablet pressures generated therein when the tablet forming punches are brought together. The signal produced by the sensing equipment is used for controlling feed to the tablet dies. These, however, are truly effective only for relatively lengthy variations in powder feed and are not particularly effective in handling more rapid pulsations in powder supply which are normally referred to in the industry as the starve/flood cycle. Some control over this is obtained by applying tape to control the size of the openings in the feed frame of the tableting machine, and in making various other adjustments in the powder controlling openings within such feed frame but these require long set-up times, often a matter of several hours, and even at best are not fully successful.
Accordingly, the objects of the invention include:
1. To provide a feed frame applicable to a standard tableting machine as used in the pharmaceutical industry whereby to minimize the fluctuations in density of powder within the tableting dies as a result of the starve/flood cycles normally experienced in conventional tableting machines.
2. To provide a feed frame, as aforesaid, which is in most respects substantially similar to presently known feed frames and which can therefore be utilized in a known manner on presently known equipment.
3. To provide a feed frame, as aforesaid, which can be obtained by relatively simple modification of presently known feed frames whereby to utilize in an improved manner feed frames already in existence.
4. To provide a feed frame, as aforesaid, which can be adjusted as needed in a simple manner to adapt a given feed frame to powders having given flow characteristics.
5. To provide a feed frame, as aforesaid, which will minimize the set-up time required to adjust the feed frame to a given powder.
6. To provide a feed frame, as aforesaid, which, when once properly adjusted, will be self-compensating for variations in the quantities of powder supplied to it and supply substantially uniform quantities of powder to the successively presented tableting dies.
The feed frame of the invention will have other and further advantages as will be apparent to persons acquainted with equipment of this general type upon reading the following specification and inspection of the accompanying drawings.