Dispenser with low-material sensing system

摘要

Apparatus, systems and methods for dispensing sheet material from a roll which include a low-material sensing system. The low-material sensing system provides an indication when the sheet material approaches depletion or is depleted so that the depleted sheet material roll can be replaced with a full roll. The low-material sensing system determines that the sheet material is depleted or near depletion by comparing the rotational speed of a sheet material roll from which the sheet material is unwound with the speed of the motor which produces movement of the sheet material roll when power is supplied to the motor. The sheet material roll speed increases as material is unwound while the motor speed remains relatively constant. A low-material indication is provided when the comparison reaches a threshold representative of the low-material state.

主权项

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