Dispenser with low-material sensing system

1. Apparatus for dispensing sheet material from a roll including a low-material sensing system, the apparatus comprising:

a sensor which generates a sensor signal indicative of sheet material roll rotation;

a direct current motor having an armature, the motor producing movement of the sheet material when current is supplied to the motor;

a low-material indicator; and

a controller coupled to the motor, sensor and indicator and having an analog-to-digital converter, the controller being operable to:

digitize a motor signal indicative of at least one of motor current and motor voltage;

digitize the sensor signal;

detect pulses in the digitized motor signal during motor armature rotation;

measure a time between motor signal pulses which occur after the motor is de-powered and is coasting, the time being indicative of motor rotational speed;

detect the digitized sensor signal during sheet material roll rotation and determine sheet material roll rotational speed therefrom;

compute a ratio of the rotational speeds; and

activate the indicator when the ratio reaches a threshold representative of a low-material state.

2. The dispenser of claim 1 wherein the indicator is selected from the group consisting of visual indicators and audible indicators.

3. The dispenser of claim 2 wherein the visual indicator is a lamp.

4. The dispenser of claim 1 wherein the controller is further operable to:

detect contiguous motor signal pulses after the motor is de-powered and is coasting; and

measure the time between the first and last of the contiguous pulses.

5. The dispenser of claim 4 wherein the contiguous pulses comprise three contiguous pulses.

6. The dispenser of claim 1 wherein the controller is further operable to ignore the first motor signal pulse after the motor is de-powered.

7. The dispenser of claim 6 wherein the controller is further operable to measure the time between the first and third pulses after the ignored pulse.

8. The dispenser of claim 1 wherein the sensor is an optical sensor responsive to reflectivity of a variable reflectivity pattern on the sheet material roll.

9. The dispenser of claim 8 wherein the optical sensor is a bar code sensor which senses a bar code on the sheet material roll.

10. The dispenser of claim 9 wherein the sheet material is wound on a core and the bar code is located on a core inner surface.

11. The dispenser of claim 10 further including:

a sheet material roll support; and

the bar code sensor is on the roll support.

12. The dispenser of claim 11 wherein the bar code sensor comprises:

an optical source operable to direct optical energy toward the bar code; and

an optical detector operable to receive optical energy from the bar code to generate the sensor signal.

13. The dispenser of claim 10 wherein the core inner surface includes a plurality of bar codes.

14. The dispenser of claim 13 wherein each of the plurality of bar codes is identical to the other.

15. The dispenser of claim 14 further comprising a quiet zone between each of the bar codes.

16. The dispenser of claim 15 wherein the bar code sensor generates the sensor signal during sheet material roll rotation, the sensor signal includes pulses associated with the bar codes and quiet zones and the controller is further operable to measure the time between a first pulse edge after the quiet zone and a second pulse edge thereafter, such time being indicative of sheet material roll rotational speed.

17. A method for controlling a motor-driven sheet material dispenser to provide an indication that the supply of sheet material on a roll is low, the method comprising:

powering a DC motor having an armature to produce movement of the sheet material roll;

digitizing a motor signal indicative of at least one of motor current and motor voltage;

digitizing a sensor signal indicative of sheet material roll rotation;

detecting pulses in the digitized motor signal during motor armature rotation;

measuring a time between motor signal pulses which occur after the motor is de-powered and is coasting, the time being indicative of motor rotational speed;

detecting the digitized sensor signal during sheet material roll rotation and determining sheet material roll rotational speed therefrom;

computing a ratio of the rotational speeds; and

providing an indication when the ratio reaches a threshold representative of the supply of sheet material being low.

18. The method of claim 17 wherein the sheet material roll includes a bar code and the method further comprises sensing the bar code with a sensor and outputting the sensor signal corresponding to the bar code.

19. The method of claim 17 wherein providing the indication further comprises activating an indicator selected from the group consisting of visual indicators and audible indicators.

20. The method of claim 17 wherein:

detecting pulses in the digitized motor signal includes detecting contiguous motor signal pulses after the motor is de-powered and is coasting; and

measuring the time between motor signal pulses includes measuring the time between the first and last of the contiguous pulses.

21. The method of claim 20 wherein detecting pulses in the digitized motor signal further includes detecting three contiguous motor signal pulses.

22. The method of claim 17 further including ignoring the first motor signal pulse after the motor is de-powered.

23. The method of claim 22 wherein measuring the time between motor signal pulses further includes measuring the time between the first and third motor signal pulses after the ignored motor signal pulse.

24. The method of claim 23 wherein the bar code is preceded by a quiet zone and the method further includes measuring the time between a first pulse edge after the quiet zone and a second pulse edge thereafter, the time being indicative of sheet material roll rotational speed.

25. The method of claim 24 wherein the sheet material roll is on a core and the bar code is on an inner surface of the core.

26. The method of claim 25 wherein the core inner surface includes a plurality of bar codes.

27. The method of claim 26 wherein each of the plurality of bar codes is identical to the other.

28. The method of claim 26 wherein the core inner surface further includes a quiet zone between each of the bar codes.

29. The method of claim 17 wherein the sheet material roll includes a bar code having elements of known width and the sensor signal includes pulses corresponding to the known widths.

30. Apparatus for dispensing sheet material from a roll including a low-material sensing system, the apparatus comprising:

a sensor which generates a sensor signal indicative of sheet material roll rotation;

a DC motor having an armature, the motor producing movement of the sheet material roll when power is supplied to the motor and having a motor signal indicative of at least one of motor current and motor voltage, the motor signal including pulses when the motor is powered and when the motor is coasting after de-powering;

a low-material indicator; and

a circuit coupled to the sensor, motor and indicator which supplies to a processing device a digitized motor signal and a digitized sensor signal;

the processing device being operable to:

detect pulses in the digitized motor signal during motor armature rotation;

measure a time between motor signal pulses which occur after the motor is de-powered and is coasting, the time being indicative of motor speed;

detect pulses in the digitized sensor signal during sheet material roll rotation and determine sheet material roll rotational speed therefrom;

compute a ratio of the rotational speeds; and

activate the indicator when the ratio reaches a threshold representative of a low-material state.