Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B21/00—Machines or devices using grinding or polishing belts; Accessories therefor
  • B24B21/04—Machines or devices using grinding or polishing belts; Accessories therefor for grinding plane surfaces
  • B24B21/06—Machines or devices using grinding or polishing belts; Accessories therefor for grinding plane surfaces involving members with limited contact area pressing the belt against the work, e.g. shoes sweeping across the whole area to be ground
  • B24B21/08—Pressure shoes; Pressure members, e.g. backing belts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
  • B24B49/16—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation taking regard of the load

Definitions

• the present invention relates to sanding devices and refers to a pressing device for sanding machines fit for pressing an abrasive mean against a surface, also a complex three-dimensional surface, allowing to obtain homogeneous finishes.
• the pressing devices, or buffers used in the known sanding machines have mobile sectors, which press the abrasive belt on the surface to be smoothed.
• the sectors are subjected to the same force and have a position determined by the portion profile to be sanded.
• the main object of the present invention is to propose a device fit to independently operate each sector to make possible a perfect smoothing also of complex three-dimensional surfaces.
• Another object is to propose a very simple and economic device fit to operate each sector in a predictive way and thus without needing feedback sensor elements.
• Further object is to propose a device feedback controlled for an accurate and continuous adjustment of the force transmitted by each sector.
• the pressing device object of the present invention has independent mobile sectors each one fit to exert, on the surface to be sanded, a continuously adjustable force.
• each pressing sector is operated by means of a respective pneumatic actuator, in a chamber of which, or in both chambers, compressed air is introduced at periodical impulses whose unitary period and whose number are opportunely dosed (Pulse Wide Modulation or "PWM”) through solenoid valves operated by a digital control programmable mean with traditional logic, or with Fuzzy logic and in which the number and the period of the impulses, required to obtain the pressure variations, are stored.
• PWM Pulse Wide Modulation
• the expected pressure, and thus the optimal force transmitted to the mobile sector, is therefore reached in a predictive way.
• the device operates a constant and accurate feedback control of the pressing force, independently of external interferences such as, for instance, environmental variations and irregularity of the supply pressure of the sector actuators, by means of optional sensors suitable to close the feedback loop by communicating to the control means the real value of the reached pressure and/or force allowing a program, which is contained in said control means and which includes a feedback control algorithm, to correct possible errors in the desired values.
• figure 1 shows a schematic front view of the device having a plurality of mobile sectors and in an operating condition.
• figure 2 shows a schematic view of an actuator of a mobile sector of figure 1 and operation and control means.
• figures from 3 to 5 show variants of the operation and control means of figure 2.
• numeral 100 indicates the pressing device for sanding machines object of the present invention.
• the sanding machine includes sanding mean 30, having an abrasive belt 29, rotating with closed loop around at least three rolls, whose at least one is a motor roll and at least one is a tensioning roll.
• the sanding mean 30 may include translation means 31 of the panel 3 to progressively sand this latter by means of the abrasive belt 29.
• the device 100 is provided with a plurality of mobile sectors 1 fit to transmit pressing forces to the sanding mean 30 to bring this latter against the surface, flat or shaped in two or three dimensions, of a panel 3 to be finished.
• a slipping mean 4 is interposed, fit to share the pressing forces exerted by said sectors 1 and to reduce the frictions.
• the slipping mean 4 includes at least a distribution layer of the pressing forces consisting of a thin continuous belt made of steel or carried out by links or articulated plaques or a linenized rubber plate, and at least an anti-friction layer made of felt or material with graphite or Teflon.
• the slipping mean 4 may include also further layers, for instance made of foam-rubber or elastic foam.
• the slipping mean 4 may be fixed or in motion, for instance, perpendicular to the panel 3 motion.
• the slipping mean 4 may further include a set of fixed layers and a set closed loop layers, moved with rotary motion.
• Each mobile sector 1 is independently moved between an operating condition L and a rest condition from the sanding mean 30, by means of a respective actuator 5 consisting of a double effect pneumatic cylinder.
• each sector 1 is positioned by the actuator 5 in correspondence of the sanding mean 30 and transfers on this latter a pressing force generated by the actuator 5 and fit to cause the contact, and therefore the smoothing, of the corresponding portion of the panel 3 by the sanding mean 30.
• each sector 1 is positioned by the actuator 5 at the maximum distance from the panel 5 to allow the insertion or the exit of said panel 5 from the sanding machine.
• the actuator 5 is fed by a first source of pressured fluid 11, for instance consisting in the exit of a first pressure switch of a compressed air tank.
• Each mobile sector 1 is connected to the free end of a rod 7 of a piston 6 of the relative actuator 5.
• the piston 6 separates a first chamber 9 from a second chamber 8 crossed by the rod 7.
• the first chamber 9 is connected 11 to the first source of gaseous fluid through respective valve means 42 operated by control means 14.
• the second chamber 8 is connected to a duct directly coupled to a second source of pressured fluid 10, for instance, consisting in an exit of a second pressure switch of the compressed air tank, regulated at a pressure value lower than the first pressure switch value.
• the valve means 42 include a solenoid valve 12 of PWM type operated by the control means 14 by a program that regulates in a predictive way the pressing force exerted onto the relative mobile sector 1 causing at least a number and an unitary duration of periodic opening impulses of said at least solenoid valve 12 for producing a difference of pressure between the rooms 8, 9 applying to the piston 6 a differential pressure corresponding to said pressing force.
• the valve means 42 have a three-ways body and are operated by the control means 14, to set the first chamber 9 of the related actuator 5 alternatively in a closing condition, flow communication condition with the first source 11 by means of said opening impulses or connection condition with the atmospheric environment to maintain unchanged the pressure of the first chamber 9, to increase the pressure by moving the sector 1 in the operating condition and/or to increase the pressing force, to reduce the pressure.
• the control means 14 consist of a programmable microprocessor controller or an industrial computer or a PLC or, preferably, a personal computer PC and they are provided with interfaces 15 for the independent operation of each valve mean 42.
• the device operation provide that, starting from the rest condition in which the pressure of the second chamber 8 maintains elastically close the related sector 1 to the respective actuator 5, the control means 14 calculate the number and the unitary duration of periodical opening impulses of the PWM-type solenoid valve 12 corresponding to the pressure value requested in the first chamber 9. Consequently the solenoid valve 12 connects in flow communication intermittently the first chamber 9 with the first source 11 and the piston 6 goes down and transmits by means of the rod 7 the pressing force to the sector 1 which therefore presses the sanding mean 30 against the related portion of panel 3 exerting a pressing force with a predetermined value that can be different for each mobile sector 1.
• the control means 14 operate the closing of the solenoid valve 12 to maintain constant the position and the pressing force of the sector 1 up to a variation of these latter. A predetermined reduction or increase of said force is obtained by the control means 14 operating respective opening impulse sequences of the first chamber respectively toward the atmospheric environment and toward the first source 11.
• the control means operate the return of the sector 1 in rest condition connecting the second chamber 9 in flow communication with the atmospheric environment through the valve means 42 for a predetermined total time sufficient to exhaust the pressure of this last chamber.
• the second chamber 8 behaves like an elastic mean that exerts on the piston 6 a force in the direction of the first chamber 9.
• a spring or an other equivalent mean is provided for operating as the second chamber 8.
• valve means 42 are of the type with two separated valve bodies each one having two ways, and for the presence of transducer mean 16 associated to each actuator for transmitting to the control means 14 data regarding the position of each sector 1.
• Each transducer mean 16 consists of a potentiometer or a rotary or linear encoder, connected to the rod 7.
• control means 14 operate opening impulses of the valve means 42 of each actuator 5 for introducing compressed fluid into the related first chamber 9 till said impulses cause corresponding movements of the respective sector 1.
• the contact of this latter with the panel 3 surface causes a reduction or interruption of said movements.
• control means 14 determine the number and the duration of the opening impulses of the PWM solenoid valve 12 in order to transmit the predefined pressing force to the sector 1.
• each mobile sector 1 is associated to respective sensor means 44 connected to the control means 14 in order to provide these latter with data regarding the pressing force of the sector 1.
• Each sensor mean 44 includes a pressure sensor 46 of the first chamber 9 and a pressure sensor Furthermore, in the variant of figure 4 the second chamber 9 is fed by respective valve means 42 controlled by control means 14 and connected to the first source of pressured fluid 11.
• valve means 42 are common solenoid valves or solenoid valves for PWM opening impulse operations.
• the control means 14 include a feedback control program, for instance of proportional type, for operating the valve means 42 of the first 9 and second 8 chambers.
• first chamber 9 of the preferred embodiment may have a related pressure sensor 46 for a feedback correction of the pressure values of said chamber.
• the variant of figure 5 differs from the variant of figure 4 in that the valve means 42 are of the type with two separated valve bodies, each having two-way, and in that each sensor mean 44 includes a load cell 45 fixed to a related actuator mean 5, for instance between the rod 7 and the sector 1.
• the main advantage of the present invention is to provide a device fit to operate each sector independently to make possible a perfect smoothing also of complex three-dimensional surfaces controlling said operation in predictive way or in negative feedback.
• Further advantage of the present invention is to provide a device having a simple manufacturing, low cost and high reliability.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Confectionery (AREA)
• Reduction Or Emphasis Of Bandwidth Of Signals (AREA)
• Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)
• Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)

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Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (3)

Citations (5)

• 2000
  • 2000-10-16 IT IT2000PS000037U patent/IT251598Y1/it active
• 2001
  • 2001-10-15 WO PCT/IB2001/001928 patent/WO2002032623A1/en active Application Filing
  • 2001-10-16 SM SM200100021A patent/SM200100021A/it unknown

Patent Citations (5)

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