Injection unit with a piston position measurement system

1. An injection unit comprising:

(a) a cylinder casing comprising an inner cylindrical surface extending along an axis;

(b) a piston housed in the casing and translatable along the axis between an advanced and a retracted position, the piston comprising a piston radial surface in facing relation to the inner cylindrical surface, the piston radial surface comprising a measurement detection feature;

c) a probe fixed relative to the cylinder casing, the probe communicating with the measurement detection feature when the piston is in and moving between the advanced and retracted positions to measure the translation of the piston,

wherein the cylinder casing comprises an outer surface spaced radially outward from the inner cylindrical surface and a cavity extending therebetween, the cavity having opposed open ends at the inner cylindrical surface and the outer surface, and wherein at least a portion of the probe is received within the cavity.

2. The injection unit of claim 1 , further comprising a pressure chamber extending radially between the inner cylindrical surface and the piston radial surface.

3. The injection unit of claim 2 , wherein the pressure chamber contains a fluid to move the piston towards one of the advanced position and the retracted position when pressurized.

4. The injection unit of claim 1 , wherein the probe extends through the cylinder casing.

5. An injection unit comprising:

a) a cylinder casing comprising an inner cylindrical surface extending along an axis;

b) a piston housed in the casing and translatable along the axis between an advanced and a retracted position, the piston comprising a piston radial surface in facing relation to the inner cylindrical surface, the piston radial surface comprising a measurement detection feature;

c) a probe fixed relative to the cylinder casing, the probe communicating with the measurement detection feature when the piston is in and moving between the advanced and retracted positions to measure the translation of the piston,

wherein the measurement detection feature comprises a plurality of annular piston teeth concentric with the axis and spaced axially apart along the piston radial surface, and

wherein the probe comprises a gear having gear teeth extending radially inwardly of the inner surface, the gear teeth engaged with the annular piston teeth, wherein translation of the piston induces rotation of the gear.

6. The injection unit of claim 5 , wherein the probe further comprises a shaft rotationally driven by the gear, the shaft coupled to a sensor for sensing rotation of the shaft.

7. The injection unit of claim 5 , further comprising rotary drive means coupled to the piston for selectively rotating the piston about the axis while the piston translates within the cylinder casing.

8. The injection unit of claim 7 , wherein the piston is rotated relative to the cylinder casing by the rotary drive means.

9. An injection unit comprising:

a) a cylinder casing comprising an inner cylindrical surface extending along an axis;

b) a piston housed in the casing and translatable along the axis between an advanced and a retracted position, the piston comprising a piston radial surface in facing relation to the inner cylindrical surface; the piston radial surface comprising a measurement detection feature;

c) a pressure chamber extending radially between the inner cylindrical surface and the piston radial surface, the pressure chamber communicating with a source of pressurized fluid for urging the piston towards one of the advanced and retracted positions; and

d) a probe extending through the cylinder casing and in communication with the measurement detection feature to measure translation of the piston when in and moving between the advanced and retracted positions,

wherein the measurement detection feature comprises a plurality of annular piston teeth concentric with the axis and spaced axially apart along the piston radial surface, and

wherein the probe comprises a gear comprising gear teeth extending into the pressure chamber, the gear teeth engaged with the annular piston teeth, wherein translation of the piston induces rotation of the gear.

10. The injection unit of claim 9 further comprising a shot cavity for holding an injection compound, wherein translation of the piston towards the retracted position is associated with filling the shot cavity with the injection compound, and translation towards the advanced position is associated with injecting the injection compound from the shot cavity into the mold, and wherein the pressure chamber urges the piston towards the retracted position when pressurized.

11. The injection unit of claim 9 , wherein the cylinder casing comprises an outer surface spaced radially outward from the inner cylindrical surface and a cavity extending therebetween, the cavity having opposed open ends at the inner cylindrical surface and the outer surface, and wherein at least a portion of the probe is received within the cavity.

12. The injection unit of claim 9 , wherein the probe further comprises a shaft rotationally driven by the gear, the shaft coupled to a sensor for sensing rotation of the shaft.

13. An injection unit comprising:

a) a cylinder casing comprising an inner cylindrical surface extending along an axis;

b) a piston housed in the casing and translatable along the axis between an advanced and a retracted position, the piston comprising a piston radial surface in facing relation to the inner cylindrical surface; the piston radial surface comprising a measurement detection feature;

c) a pressure chamber extending radially between the inner cylindrical surface and the piston radial surface, the pressure chamber communicating with a source of pressurized fluid for urging the piston towards one of the advanced and retracted positions; and

d) a probe extending through the cylinder casing and in communication with the measurement detection feature to measure translation of the piston when in and moving between the advanced and retracted positions,

wherein the measurement detection feature comprises an axially tapering portion of the piston radial surface, and wherein the probe comprises a distance sensor sensing the distance of the piston radial surface from the distance sensor.

14. An injection unit comprising:

a) a cylinder casing comprising an inner cylindrical surface extending along an axis;

b) a piston housed in the casing and translatable along the axis between an advanced and a retracted position, the piston comprising a piston radial surface in facing relation to the inner cylindrical surface, the piston radial surface comprising a measurement detection feature;

c) a pressure chamber extending radially between the inner cylindrical surface and the piston radial surface, the pressure chamber containing a fluid for translating the piston when pressurized; and

d) a probe fixed relative to the cylinder casing and extending through the fluid in the pressure chamber, the probe communicating with the measurement detection feature to continuously measure the axial position of the piston relative to the casing when the piston moves to and between the advanced and retracted positions.

15. The injection unit of claim 14 , wherein the pressure chamber is disposed axially between first and second seal journals, the first and second seal journals providing sealed sliding engagement between the inner cylindrical surface and the piston radial surface.

16. The injection unit of claim 15 , wherein the axial spacing between the first and second seal journals remains constant when the piston is in and moving between the advanced and retracted positions.

17. The injection unit of claim 14 further comprising a shot cavity for holding an injection compound, wherein translation of the piston towards the retracted position is associated with filling the shot cavity with the injection compound, and translation towards the advanced position is associated with injecting the injection compound from the shot cavity into the mold, and wherein the pressure chamber urges the piston towards the retracted position when pressurized.

18. The injection unit of claim 14 , wherein the cylinder casing comprises an outer surface spaced radially outward from the inner cylindrical surface and a cavity extending therebetween, the cavity having opposed open ends at the inner cylindrical surface and the outer surface, the open end at the inner cylindrical surface opening into the pressure chamber, and wherein at least a portion of the probe is received within the cavity.

19. The injection unit of claim 14 , wherein the measurement detection feature comprises a plurality of annular piston teeth concentric with the axis and spaced axially apart along the piston radial surface.

20. The injection unit of claim 19 , wherein the probe comprises a gear comprising gear teeth extending into the pressure chamber, the gear teeth engaged with the annular piston teeth, wherein translation of the piston induces rotation of the gear.

21. The injection unit of claim 20 , wherein the probe further comprises a shaft rotationally driven by the gear, the shaft extending from inside the pressure chamber to outside the cylinder casing and oriented perpendicular to the axis, and the shaft coupled to a sensor for sensing rotation of the shaft.

22. The injection unit of claim 14 , wherein the measurement detection feature comprises an axially tapering portion of the piston radial surface, and wherein the probe comprises a distance sensor sensing the distance of the piston radial surface from the distance sensor.

23. The injection unit of claim 14 , wherein the piston is rotatable about the axis while axially translating within the cylinder casing.