Details for Patent: 7,819,075

Title:	Inhaler device counter
Abstract:	Inhaler counter (20) comprising a counter housing (390), a rocker arm (200) with a pawl (210), the rocker arm being pivotally supported by the housing and arranged to perform a rocker movement in response to a linear actuation motion, a return spring (220) for resetting the rocker arm, a ratchet wheel (230) engagable with the pawl to convert the movement of the rocker arm into an incremental rotational motion of an axle arrangement (240) advancing a display means (60), the axle arrangement further comprising a back rotation prevention means (280) in the form of a spring loaded friction brake and a worm gear, the display means comprising rotatable indicator means (120) with teeth that engage the worm-gear and a stationary scale.
Inventor(s):	Bowman; Nic (Cambridge, GB), Bradshaw; Douglas (Royston Herts, GB), Sorby; Lennart (Uppsala, SE)
Assignee:	AstraZeneca AB (Sodertalje, SE)
Filing Date:	Sep 08, 2009
Application Number:	12/555,559
Claims:	1. An inhaler counter comprising a ratchet wheel, a pawl and a display, the ratchet wheel and the pawl being arranged to transform a linear actuation motion into a rotational motion that advances the display by the pawl engaging a tooth of the ratchet wheel, the pawl and ratchet wheel arranged to effect disengagement of the pawl from the engaged tooth of the ratchet wheel by establishing abutment of the pawl and ratchet wheel at a lever point following the engaged tooth with respect to a direction of rotational motion of the ratchet wheel; wherein the lever point on the ratchet wheel is located on a tooth subsequent to the engaged tooth; and, wherein the subsequent tooth includes a straight back surface and the pawl includes a protrusion on a pawl counter surface that abuts the straight back surface to form the lever point. 2. An inhaler comprising: an inhaler canister; an actuator body receiving the inhaler canister, the inhaler being actuated by linear motion of the canister relative to the actuator body; and an inhaler counter according to claim 1 coupled to the inhaler canister. 3. An inhaler counter comprising: a ratchet wheel and a pawl, the ratchet wheel and the pawl being arranged to transform a linear actuation motion into a rotational motion advancing a display by the pawl engaging a tooth of the ratchet wheel, wherein the ratchet wheel has teeth with a convex back surface, the ratchet wheel and the pawl having a maximum reset torque dependent on a curvature of the convex back surface, a diameter of the ratchet wheel, a friction coefficient between the ratchet wheel material and the pawl material, and a spring constant of the pawl, wherein the curvature of the convex back surface is selected to minimize the maximum reset torque. 4. An inhaler comprising: an inhaler canister; an actuator body receiving the inhaler canister, the inhaler being actuated by linear motion of the canister relative to the actuator body; and an inhaler counter according to claim 3 coupled to the inhaler canister. 5. A method of providing a ratchet wheel and a pawl arranged to transform a linear actuation motion into a rotational motion advancing a display by the pawl engaging a tooth of the ratchet wheel, the method comprising: selecting diameter, number of teeth, and material for the ratchet wheel, the teeth having a convex back surface; selecting shape and material for the pawl; determining a maximum reset torque for the ratchet wheel and pawl arrangement as a function of ratchet wheel diameter, friction coefficient between the ratchet wheel material and the pawl material, pawl spring constant, and curvature of the convex back surface; and selecting the curvature of the convex back surface so as to minimize the maximum reset torque.