DESC:FIELD OF THE INVENTION
This invention relates to a rotary tablet making machine.

BACKGROUND OF THE INVENTION
Dosages of pharmaceutical or neutraceutical substances in powder form are pressed into tablets in a tablet making machine or tablet press for ease and convenience of handling the powder and making dosages of the powder and for ease and convenience of patients to take the dosages. Tablets also help to maintain accuracy of dosages.

A typical rotary tablet making machine comprises a turret disposed for cyclic rotation about a vertical axis and about a feeding station, a pre-compression station, a compression station and an ejection station. The turret comprises a plurality of tablet forming transverse die holes formed therethrough circumferentially spaced apart from one another. The die holes are dimensioned to correspond to the size, shape and dosage of the tablets to be made in the machine. A plurality of pairs of lower and upper punches corresponding to the die holes are rotatably held with the turret vertically aligned with the die holes. Each of the punches consists of a punch head and a punch tip at opposite ends thereof. The punch tips are dimensioned to register with the die holes. The lower punches are up and down movably disposed below the turret with the tips thereof engaged in the die holes from the bottom of the turret and the upper punches are up and down movably disposed above the turret with the tips thereof engaged in the die holes from the top of the turret. The lower punches and upper punches are rotatable with the turret in the same direction in a synchronized manner.

The feeding station comprises a feeder unit and each of the pre-compression and compression stations comprises a stationary bottom actuator circular disc disposed below the turret in the radial direction of the bottom actuator disc in the path of the lower punches and mounted on a stationary horizontal shaft. Each of the pre-compression and compression stations also comprises a stationary top actuator circular disc disposed above the turret in the radial direction of the top actuator disc in the path of the upper punches and mounted on another stationary horizontal shaft. The bottom and top actuator discs at each of the precompression and compression stations are vertically aligned. The heads of the lower punches are engageable and slidable against the outer circumference of the bottom actuator disc at each of the precompression and compression stations. The heads of the upper punches are engageable and slidable against the outer circumference of the top actuator disc at each of the precompression and compression stations. The ejection station comprises a cam disposed below the turret in the direction of the outer surface of the cam in the path of the lower punches and mounted to the machine frame.

In a cycle of operation of the machine, the turret rotates about its vertical axis and about the various stations with the punches starting from the feeding station. The feeder unit at the feeding station feeds powder to be pressed into a tablet, into a die hole at the feeding station returning empty from the ejection station with the tip of the corresponding upper punch retracted from the die hole and positioned above the turret and the tip of the corresponding lower punch remaining in the die hole. As the upper punch is positioned above the turret at the feeding station, powder can be fed into the empty die hole at the feeding station. Because of the presence of the tip of the lower punch in the empty die hole, the die hole remains closed from the bottom of the turret with the tip of the lower punch. Therefore, the powder in the die hole does not flow out from the die hole. During the continued rotation of the turret along with the punches, the die hole filled with the powder passes through the pre compression station, compression station and ejection station successively.

While the powder filled die hole passes through the pre-compression station, the respective lower punch engages against and moves up on the outer circumference of the bottom actuator disc at the pre-compression station and the powder in the respective die hole gets precompressed with the tip of the lower punch from the bottom of the turret. Simultaneously, the corresponding upper punch engages against and moves down on the outer circumference of the top actuator disc at the pre-compression station and its tip enters the die hole and precompress the powder in the die hole from the top of the turret to form a tablet. While the die hole with the precompressed tablet passes through the compression station, the lower punch and the upper punch at the compression station engage against and move up and down on the outer circumference of the bottom and top actuator discs, respectively, to compress the pre compressed tablet in the die hole between the lower and upper punch tips.

During further rotation of the turret with the punches and the precompressed tablet in the die hole through the ejection station, the lower punch at the ejection station engages against and slides up on the outer surface of the cam at the ejection station and pushes the tablet out of the die hole. In order to facilitate ejection of the tablet, the corresponding upper punch moves up and out of the die hole at the ejection station. The tablet is taken for further processing such as coating or checking for weight variations. The turret with the empty die hole and the punches returns to the feeding station to start the next cycle of operation of the machine.

In the above machine, the compression ratio of the tablets at the compression station depends on the dwell time of the lower and upper punches at the compression station. Dwell time for the lower punches and upper punches at the compression station is the duration for which the lower punches will be at the top most circumferential position of the bottom actuator disc and the upper punches will be at the bottom most circumferential position of the top actuator disc. Because of the circularity of the outer circumferences of the bottom and top actuator discs, the top most circumferential area of contact between lower punch heads and bottom actuator disc and the bottom most circumferential area of contact between the upper punch heads and top actuator disc are very narrow to the extent of being line contacts.

Therefore, while the lower punches and upper punches are performing the compression of the tablets, they are at the top most circumferential position of the bottom actuator disc and bottom most circumferential position of the top actuator disc only for a very short dwell time respectively. As a result, the duration of compression is very short and the compression ratio of the tablets is very limited. This may give rise to weight and thickness variations of the tablets and dosage inaccuracies, which is not desirable and acceptable, especially in the case of pharmaceuticals and neutraceuticals.

Because of the limited top most circumferential area of contact between the lower punch heads and bottom actuator disc and limited bottom most circumferential area of contact between the upper punch heads and top actuator disc and resultant short dwell time, it is also not possible to increase the rpm of the machine to increase productivity. Increase in rpm of the machine will further reduce the dwell time and compression ratio of the tablets. Increase in rpm of the machine will also increase vibrations leading to noise generation and wear and tear to the punches and the actuator discs at the compression station. Because of the limited surface area of contact available between the lower punches and bottom actuator disc at the top most circumferential position of the lower punches and between the upper punches and the top actuator disc at the bottom most circumferential position of the upper punches, it is also not possible to compress the tablets at different or variable compression ratios.

There is thus need for rotary tablet making machines having increased dwell time at the compression station to obviate problems described above.

DESCRIPTION OF THE INVENTION
According to the invention there is provided a rotary tablet making machine, comprising a turret disposed for cyclic rotation about a vertical axis and about a feeding station, a pre-compression station, a compression station and an ejection station, the turret comprising a plurality of tablet forming transverse die holes formed therethrough circumferentially spaced apart from one another and dimensioned to correspond to the size, shape and dosage of the tablets to be made and a plurality of pairs of lower and upper punches corresponding to the die holes vertically aligned with the die holes and rotatably held with the turret for synchronised rotation with the turret in the same direction, each of the punches having a punch head and a punch tip at opposite ends thereof, the punch tips being dimensioned to register with the die holes, the lower punches being up and down movably disposed below the turret with the punch tips thereof engaged in the die holes from the bottom of the turret and the upper punches being up and down movably disposed above the turret with the punch tips thereof engaged in the die holes from the top of the turret, wherein the compression station comprises stationary bottom actuator circular disc disposed in the path of the lower punches in the radial direction of the bottom actuator disc and having a first flat surface at the top most circumference thereof and a stationary top actuator circular disc disposed vertically aligned with the bottom actuator disc in the path of the upper punches in the radial direction of the top actuator disc and having a second flat surface at the bottom most circumference thereof matching with and aligned with the first flat surface at the top most circumference of the bottom actuator disc, and wherein each of the bottom and top actuator discs comprises an endless roller chain rotatably mounted over the respective actuator disc, each of the roller chains consisting of a plurality of compression segments, each compression segment having a flat outer face corresponding to and matching with the first and second flat surfaces at the outer circumference of the respective actuator disc and a roller rotatably held at the inner face of the compression segment making a line contact with the outer circumference of the respective actuator disc and wherein the flat outer faces of the compression segments together describing the outer circumference of the respective roller chain for the punch heads of the lower and upper punches to engage against the flat outer faces of the respective roller chain.

DESCRIPTION OF DRAWINGS
Schematic Figs 1, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b, 5, 6, 7, 8, 9 and 10 of the drawings accompanying this specification correspond to Figs 1, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b, 5, 6, 7, 8, 9 and 10 of the provisional specification drawings with the inclusion of certain additional reference numerals and elimination of certain reference numerals to better describe and explain the invention. Figs 11 and 12 of the drawings accompanying this specification are schematic views of a lower punch and an upper punch, respectively.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION
As illustrated in Figs 1 to 12 of the drawings accompanying this specification, the rotary tablet making machine 1 comprises a turret 2 disposed for cyclic rotation about a vertical axis 3 and about a feeding station 4, pre-compression station 5, compression station 6 and an ejection station 7 (Fig 1). The turret comprises a plurality of tablet forming transverse die holes 8 formed therethrough circumferentially spaced apart from one another. The die holes are dimensioned to correspond to the size, shape and dosage of the tablets to be made in the machine. A plurality of pairs of lower punches 9 and upper punches 10 are vertically aligned with a die hole and are rotatably held with the turret for synchronised rotation with the turret in the same direction. Each of the lower punches has a punch head 9a at the lower end thereof and a punch tip 9b at the upper end thereof (Fig 11). Each of the upper punches has a punch head 10a at the lower end thereof and a punch tip 10b at the upper end thereof (Fig 12). The punch tips are dimensioned to register with the die holes. The lower punches are up and down movably disposed below the turret with the tips thereof engaged in the die holes from the bottom of the turret and the upper punches are up and down movably disposed above the turret with the tips thereof engaged in the die holes from the top of the turret.

The compression station 6 comprises a stationary bottom actuator circular disc 13 disposed in the path of the lower punches in the radial direction of the bottom actuator disc and mounted on a stationary horizontal shaft 14. The bottom actuator disc consists of a first flat surface15 at the top most outer circumference thereof. The compression station also comprises a stationary top actuator circular disc 16 disposed vertically aligned with the bottom actuator disc in the path of the upper punches in the radial direction of the top actuator disc and mounted on a stationary horizontal shaft 17. The top actuator disc consists of a second flat surface 18 at the bottom most outer circumference thereof matching with and aligned with the first flat surface on the bottom actuator disc.

Each of the bottom actuator and top actuator discs comprises an endless roller chain 19 roatably mounted over the respective actuator disc. The roller chain consists of a plurality of compression segments 20 arranged in a circular configuration around the respective actuator disc. Each of the compression segments consists a compression block 21 having a flat outer surface 22, a transverse hole 23 therethrough and a slit 24 at the inner surface thereof. A roller 25 is rotatably located in the transverse hole in each of the compression blocks exposed through the slit in the compression block. The exposed surface of the roller makes a line contact with the outer circumference of the respective actuator disc and the roller is slidable and rotatable on the outer circumference of the respective actuator disc. The compression segments consisting of compression blocks with the rollers engaged in the transverse holes of the compression blocks are mounted on the respective actuator disc and held between a pair of end covers 26, 26 fitted together with screws 27. The flat outer faces 22 of the compression blocks 21 together form the outer circumference of the roller chain.

During operation of the machine 1, while a pair of lower and upper punches performs the compression of a tablet in a die hole 8 in the turret at the compression station 6, the head of the lower punch performing the compression engages against the flat outer face 22 of a compression block 21 of the roller chain of the bottom actuator disc, which compression block is on the first flat surface 15 at the top most outer circumference of the bottom actuator disc 13. The corresponding roller 25 of the compression block of the roller chain of the bottom actuator disc rotates and slides along the first flat surface 15 at the top most outer circumference of the bottom actuator disc from one end to the other end of the first flat surface making a line contact with the first flat surface and the roller chain describes a rotary motion on the bottom actuator disc in the direction of rotation of the turret and the punches. As a result, the compression block moves with the roller in the direction of rotation of the roller chain and the lower punch also moves with the compression block in the same direction without describing practically any relative motion between the lower punch and compression block and without describing any vertical displacement of the lower punch (Figs 2a, 2b and 2c).

Simultaneously the head of the corresponding upper punch performing the compression engages against the flat outer face 22 of a compression block 21 of the roller chain of the top actuator disc, which compression block is on the second flat surface 18 at the bottom most outer circumference of the top actuator disc 16. The corresponding roller 25 of the compression block of the roller chain of the top actuator disc 16 rotates and slides along the second flat surface 18 at the bottom most outer circumference of the top actuator disc 16 from one end to the other end of the second flat surface making a line contact with the second flat surface and the roller chain describes a rotary motion on the top actuator disc in the direction of rotation of the turret and the punches. As a result, the compression block moves with the roller in the direction of rotation of the roller chain and the upper punch also moves with the compression block in the same direction without describing practically any relative motion between the upper punch and compression block and without describing any vertical displacement of the upper punch (Figs 3a, 3b and 3c).

Because of the large surface area of the first and second flat surfaces 15 and 18 at the top most and bottom most outer circumferences of the bottom actuator disc 13 and top actuator disc 16, respectively, and the corresponding flat surface area of the outer faces 22 of the compression blocks 21, the dwell time for the lower and upper punches performing the compression is increased in that the flat surfaces provide increased surface area for the rollers to travel from one end to the other end of flat surfaces making line contact with the flat surfaces while the punches perform compression thereby increasing duration of travel of the respective punches from one end to the other end of the flat surfaces and the compression interval. As a result, the compression ratio of the tablets is increased.

As the compression ratio of the tablets is increased, weight and thickness variations of the tablets is practically eliminated and dosage accuracy is maintained. Because of the increase in dwell time, the rpm of the machine can be increased to increase productivity. It is also possible to get different compression ratios of the tablets by adjusting the rpm of the machine. Since there is practically no relative motion between the punches and the compression blocks at the compression station and since the rollers are rotating and sliding on the outer circumferences of the bottom actuator disc and top actuator disc in line contact, frictional forces between the compression blocks and punches and between the rollers and the outer circumference of the actuator discs, are reduced and noise and heat generation are also reduced. Vibrations of the machine are also reduced because of the flat surfaces at the outer circumferences of the actuator discs. Wear and tear of the actuator discs and punches are also reduced thereby increasing the life thereof.

The above embodiment of the invention is only illustrative of the invention and is not limitative of the scope of the invention. The invention is essentially in increasing the dwell time of the lower and upper punches performing compression of the tablets in the die holes in the turret at the compression station. The bottom and top actuators can be of a different construction and configuration. The roller chain configuration and construction can be different. The machine of the invention also can be used for making tablets of any powder besides pharmaceutical or neutraceutical powder. Variations of the invention as illustrated and described, which are obvious to a person skilled in the art are to be construed and understood to be within the scope of the invention which is defined by and encomposed within the following statement of claims.

,CLAIMS:We Claim:

1. A rotary tablet making machine, comprising a turret disposed for cyclic rotation about a vertical axis and about a feeding station, a pre-compression station, a compression station and an ejection station, the turret comprising a plurality of tablet forming transverse die holes formed therethrough circumferentially spaced apart from one another and dimensioned to correspond to the size, shape and dosage of the tablets to be made and a plurality of pairs of lower and upper punches corresponding to the die holes vertically aligned with the die holes and rotatably held with the turret for synchronised rotation with the turret in the same direction, each of the punches having a punch head and a punch tip at opposite ends thereof, the punch tips being dimensioned to register with the die holes, the lower punches being up and down movably disposed below the turret with the punch tips thereof engaged in the die holes from the bottom of the turret and the upper punches being up and down movably disposed above the turret with the punch tips thereof engaged in the die holes from the top of the turret, wherein the compression station comprises stationary bottom actuator circular disc disposed in the path of the lower punches in the radial direction of the bottom actuator disc and having a first flat surface at the top most circumference thereof and a stationary top actuator circular disc disposed vertically aligned with the bottom actuator disc in the path of the upper punches in the radial direction of the top actuator disc and having a second flat surface at the bottom most circumference thereof matching with and aligned with the first flat surface at the top most circumference of the bottom actuator disc, and wherein each of the bottom and top actuator discs comprises an endless roller chain rotatably mounted over the respective actuator disc, each of the roller chains consisting of a plurality of compression segments, each compression segment having a flat outer face corresponding to and matching with the first and second flat surfaces at the outer circumference of the respective actuator disc and a roller rotatably held at the inner face of the compression segment making a line contact with the outer circumference of the respective actuator disc and wherein the flat outer faces of the compression segments together describing the outer circumference of the respective roller chain for the punch heads of the lower and upper punches to engage against the flat outer faces of the respective roller chain.

2. The tablet making machine as claimed in claim 2, wherein each of the roller chains consists of a plurality of compression blocks, each compression block having a flat outer face corresponding to and matching with the first and second flat surfaces at the outer circumferences of the respective actuator discs, a transverse hole therethrough and a slit at the inner face thereof and a roller rotatably located in the transverse hole in the compression block exposing the roller through the slit in the compression block, the roller making a line contact with the outer circumference of the respective actuator disc and being slidable against the outer circumference of the respective actuator disc, the compression blocks being mounted on the respective actuator disc and held between a pair of end covers, the punch heads of the lower and upper punches being engageable against the flat outer faces of the compression blocks of the respective roller chains.