Web tensioning device with improved excursion control

Abstract

A web tensioning device utilizes a dancer device, either angular or linear, which can be positioned by a controlled servo motor. In a preferred embodiment, the controller for the servo motor receives an input signal based on the acceleration (positive or negative) of the dancer device caused by a web excursion and implements a compensation necessary to oppose the web excursion. The controller may also receive additional input signals indicative of the acceleration of the web itself, resulting from the web excursion.

1 . A web tensioning device for overcoming an excursion of a traveling web, comprising:
 a base;   a dancer device for engaging the web, mounted to the base for movement in response to a web excursion;   a sensor for detecting a position displacement of the dancer device arising from the web excursion and providing a sensor output signal in response to detected position displacement;   a controller coupled to the sensor to receive the sensor output signal and for generating in response thereto, a control signal indicative of a force accelerating the dancer device due to a change in web tension associated with the detected position displacement; and   a servo motor coupled to the controller and operably associated with the dancer device to apply, in response to the control output signal, an opposing compensating force to the dancer device that opposes said position displacement of said dancer device,   the magnitude of the opposing compensating force being substantially the same as that of the force accelerating.   
     
     
         2 . The web tensioning device according to  claim 1  wherein the dancer device comprises a pivotably mounted dancer arm and a dancer roller mounted to the dancer arm. 
     
     
         3 . The web tensioning device according to  claim 1  wherein the sensor comprises an angular position sensor. 
     
     
         4 . The web tensioning device according to  claim 3  wherein the dancer device comprises a pivotably mounted dancer arm and said servo motor applies to torque to the dancer arm. 
     
     
         5 . The web tensioning device according to  claim 1  wherein the sensor comprises a linear position sensor. 
     
     
         6 . The web tensioning device according to  claim 3  wherein the dancer device comprises a dancer roller mounted for linear travel and said servo motor applies a linear force to the dancer roller. 
     
     
         7 . A web tensioning device for overcoming an excursion of a traveling web, comprising:
 a base;   a dancer device comprising a dancer roller mounted for linear travel for engaging the web, mounted to the base for movement in response to a web excursion;   a linear position sensor for detecting a position displacement of the dancer device arising from the web excursion and providing a sensor output signal in response to the detected position displacement,   a controller coupled to receive the sensor output signal and for generating in response thereto, a control output signal indicative of an acceleration of the dancer device due to a change in web tension; and   a servo motor coupled to the controller and operably associated with the dancer device to apply, in response to receiving the control output signal, a linear opposing compensating force to the dancer device that opposes said position displacement of said dancer device;   the magnitude of the opposing compensating force being substantially the same as that of the force associated with the acceleration of the dancer device, so that the excursion of the web is overcome.   
     
     
         8 . The web tensioning device in accordance with  claim 7  wherein the servo motor comprises a linear motor. 
     
     
         9 . The web tensioning device in accordance with  claim 7  wherein the linear position sensor includes a laser. 
     
     
         10 . The web tensioning device in accordance with  claim 7  wherein the linear position sensor includes a doppler laser. 
     
     
         11 . The web tensioning device in accordance with  claim 7  wherein the linear position sensor includes a linear encoder. 
     
     
         12 . The web tensioning device in accordance with  claim 7  wherein the linear position sensor includes a linear transducer. 
     
     
         13 . The web tensioning device in accordance with  claim 7  wherein the linear position sensor includes an analog proximity sensor. 
     
     
         14 . The web tensioning device in accordance with  claim 7  wherein the linear position sensor includes an accelerometer. 
     
     
         15 . A web tensioning device for overcoming an excursion of the traveling web, comprising:
 a base;   a dancer arm pivotably mounted to the base for movement in response to a web excursion;   an angular position sensor for detecting an angular position displacement of the dancer arm arising from the web excursion and to provide an output signal in response to the detected position displacement;   a controller coupled to receive the sensor output signal and for generating in response thereto, a control output signal indicative of an acceleration of the dancer arm due to a change in web tension arising from the detected position displacement; and   a servo motor coupled to the controller and operably associated with the dancer arm to apply, in response to receiving the control output signal, an opposing compensating torque to the dancer device that opposes said position displacement of said dancer device,   the magnitude of the opposing compensating torque being substantially the same as that of the force associated with the acceleration of the dancer arm, so that the excursion of the web is overcome.   
     
     
         16 . The web tensioning device according to  claim 15  wherein the dancer arm has a free end portion with a dancer rotatably mounted thereon and a fixed end portion pivotably mounted to the base so as to coact with the angular position sensor and indicate relative angular displacement of the dancer arm as a web in contact with the dancer is maintained in tension. 
     
     
         17 . The web tensioning device according to  claim 15  wherein the servo motor is operably associated with the dancer arm for pivotally positioning the dancer arm by application of a compensating torque component in response to a control output signal. 
     
     
         18 . The web tensioning device in accordance with  claim 15  wherein the angular position sensor is an encoder operably associated with the fixed end portion of the dancer device and senses relative angular displacement of the dancer device. 
     
     
         19 . The web tensioning device in accordance with  claim 18  wherein the encoder is an incremental rotary optical encoder. 
     
     
         20 . The web tensioning device in accordance with  claim 15  wherein the servo motor is an electric motor. 
     
     
         21 . The web tensioning device in accordance with  claim 15  wherein the servo motor is a limited angle electric motor operably associated with the dancer device for pivoting the dancer device by application of torque in response to the control output signal. 
     
     
         22 . The web tensioning device in accordance with  claim 15  wherein the angular position sensor is a torque sensor including a tunnel-diode oscillator for detecting torque. 
     
     
         23 . A web tensioning device for overcoming an excursion of a traveling web, comprising:
 a base;   a dancer device for engaging the web, mounted to the base for movement in response to a web excursion;   a sensor for detecting a change in the movement of a portion of the web adjacent the dancer device, arising from the web excursion and to provide an output signal in response to the detected movement,   a controller coupled to receive the sensor output signal and for generating in response thereto, a control output signal indicative of an acceleration of the dancer device due to a change in web tension arising from the detected movement; and   a servo motor coupled to the controller and operably associated with the dancer device to apply, in response to receiving the control output signal, an opposing compensating force to the dancer device that opposes said detected movement of said dancer device,   the magnitude of the opposing compensating force being substantially the same as that of the force associated with the acceleration of the dancer device, so that the excursion of the web is overcome.   
     
     
         24 . The web tensioning device in accordance with  claim 23  wherein the sensor includes a laser monitoring a portion of the web adjacent the dancer device.