Method of controlling a screw in a two-stage injection unit and a system for implementing the method

1. A method of controlling a screw in a two-stage injection unit, the method executable at a computing apparatus associated with the two-stage injection unit, the method comprising:

receiving an indication of an operational parameter associated with the screw of the two-stage injection unit;

based on the indication of the operational parameter, determining a target speed (S TARGET ) for the screw, said target speed (S TARGET ) being sufficient to enable the screw to produce a required amount of material in a molten state;

causing the screw to rotate at the target speed (S TARGET ), thereby causing the screw to operate in a substantially continuous manner,

said operational parameter comprising at least: (i) an indication of recovery time (T RECOVERY ); (ii) an indication of idling time (T IDLE ); (iii) an indication of current rotational speed of the screw (S REFERENCE ); and wherein said determining comprises calculating said target speed (S TARGET ) based on a formulae expressed as:

S

TARGET

=

T

RECOVERY

T

RECOVERY

+

T

IDLE

×

S

REFERENCE

.

2. The method of claim 1 , wherein said determining a target speed (S TARGET ) for the screw comprises determining speed (S TARGET ) for the screw such that when the screw rotates at the target speed (S TARGET ), it reaches a back position at an instance in time that substantially coincides with an instant in time when the transfer stage commences.

3. The method of claim 1 , wherein said causing comprises generating a control signal representative of the target speed (S TARGET ).

4. The method of claim 3 , further comprising releasing the control signal towards a screw actuator of the screw.

5. The method of claim 1 , wherein said receiving an indication of an operational parameter comprises:

retrieving a stored operational parameter from an internal memory.

6. The method of claim 5 , wherein said stored operational parameter comprises at least one of:

an indication of linear position of the screw (P SCREW );

an indication of recovery time (T RECOVERY );

an indication of idling time (T IDLE );

an indication of current rotational speed of the screw (S REFERENCE );

an indication of a constant value (V CONSTANT ).

7. The method of claim 5 , further comprising obtaining an indication of stored operational parameter and storing the indication of the stored operational parameter in the internal memory.

8. The method of claim 7 , wherein said obtaining an indication of stored operational parameter comprises receiving the indication of stored operational parameter from at least a first sensor.

9. The method of claim 7 , wherein said obtaining an indication of stored operational parameter comprises appreciating the indication of stored operational parameter by virtue of controlling one or more functions of a molding system incorporating the two-stage injection unit.

10. The method of claim 1 , further comprising executing a verification routine configured to determine if the target speed (S TARGET ) is sufficient to obtain the required amount of material in a molten state.

11. The method of claim 10 , using an operating parameter comprising at least (i) an indication of the target speed (S TARGET ); (ii) an indication of a distance between a current linear position and a back position (D BACK POSITION ); (iii) an indication of a remaining time in a current recovery cycle (T REMAINING ); and (iv) an indication of a constant parameter (V CONSTANT ); wherein said executing a verification routine comprises calculating a current target speed (S TARGET NEW ) based on a formulae expressed as:

S

TARGET

⁢

⁢

NEW

=

D

BACK

⁢

⁢

POSITION

×

1

T

REMAINING

×

V

CONSTANT

.

12. The method of claim 11 , further comprising:

if said current target speed (S TARGET NEW ) does not equal to said target speed (S TARGET ) within a variance window, causing the screw to rotate at the current target speed (S TARGET NEW ).

13. The method of claim 12 , wherein said causing the screw to rotate at the current target speed (S TARGET NEW ) comprises generating a control signal representative of the target speed (S TARGET NEW ).

14. The method of claim 13 , further comprising releasing the control signal representative of the target speed (S TARGET NEW ) towards a screw actuator of the screw.

15. The method of claim 10 , wherein said executing a verification routine comprises executing the verification routine at a midpoint of a recovery stage.

16. The method of claim 10 , wherein said executing a verification routine comprises executing the verification routine at a one-third-point of a recovery stage.

17. The method of claim 10 , wherein said executing a verification routine comprises executing the verification routine substantially continuously throughout a recovery stage.

18. The method of claim 1 , wherein said required amount of material comprises an amount equivalent to a desired shot size.

19. A two-stage injection unit comprising:

a barrel with a screw operatively mounted therewithin;

a shooting pot in fluid communication with said barrel;

a computing apparatus operatively coupled to said screw for controlling operation thereof; the computing apparatus being configured:

receive an indication of an operational parameter associated with the screw of the two-stage injection unit;

based on the indication of the operational parameter, determining a target speed (S TARGET ) for the screw;

transmit a control signal representative of the target speed (S TARGET ) towards the screw;

whereby said control signal causes the screw to rotate at the target speed (S TARGET ) in a substantially continuous manner while producing a required amount material in a molten state,

said operational parameter comprising at least: (i) an indication of recovery time (T RECOVERY ); (ii) an indication of idling time (T IDLE ); (iii) an indication of current rotational speed of the screw (S REFERENCE ); and wherein said computing apparatus is configured to calculate said target speed (S TARGET ) based on a formulae expressed as:

S

TARGET

=

T

RECOVERY

T

RECOVERY

+

T

IDLE

×

S

REFERENCE

.

20. The two-stage injection unit of claim 19 , wherein said target speed (S TARGET ) for the screw is determined such that when the screw rotates at the target speed (S TARGET ), it reaches a back position at an instance in time that substantially coincides with an instant in time when the transfer stage commences.

21. The two-stage injection unit of claim 19 , wherein said required amount of material comprises an amount equivalent to a desired shot size.

22. A computer readable storage medium containing a program element for execution by a computing apparatus, the program element for rendering the computing apparatus to:

receive an indication of an operational parameter associated with a screw of a two-stage injection unit;

based on the indication of the operational parameter, determine a target speed (S TARGET ) for the screw, said target speed (S TARGET ) being sufficient to enable the screw to produce a required amount of material in a molten state;

cause the screw to rotate at the target speed (S TARGET ), thereby causing the screw to operate in a substantially continuous manner,

said operational parameter comprising at least: (i) an

indication of recovery time (T RECOVERY ); (ii) an

indication of idling time (T IDLE ); (iii) an indication of current rotational speed of the screw (S REFERENCE );

and wherein said computing apparatus is configured by the program element to calculate said target speed (S TARGET ) based on a formulae expressed as:

S

TARGET

=

T

RECOVERY

T

RECOVERY

+

T

IDLE

×

S

REFERENCE

.

23. The computer readable storage medium of claim 22 , wherein said target speed (S TARGET ) for the screw is determined such that when the screw rotates at the target speed (S TARGET ), it reaches a back position at an instance in time that substantially coincides with an instant in time when the transfer stage commences.