Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Program-control systems
  • G05B19/02—Program-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of program data in numerical form
  • G05B19/406—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of program data in numerical form characterised by monitoring or safety
  • G05B19/4065—Monitoring tool breakage, life or condition

Definitions

• the present invention relates generally to adaptive control systems for a machine tool and more particularly to a method and apparatus for monitoring the condition of a
• cutting tool is measured.
• indirect methods the effects of tool wear, such as variation in temperature, cutting forces, power, torque, etc. are measured.
• the indirect methods are better suited for in-process tool condition monitoring.
• Cutting force variation as a measure of tool wear, is ideally suited for automated and numerical control machining, since cutting forces change with tool wear and force measuring devices can be easily incorporated into production machines.
• Prior art force measuring systems measure the cutting force loads between two machine components.
• Prior art arrangements typically consist of one or more load cells or transducers placed between two machine components for detecting or measuring the forces acting at the interface between the two components.
• the corresponding output signal from the transducer is representative of the cutting forces generated between the tool and workpiece during the machining process.
• the transducer output signal is inputed to appropriate signal conditioning equipment, an assessment of tool condition can be obtained.
• the present invention provides a method and apparatus for monitoring cutting forces in a machine tool which requires no modification to the machine tool.
• the invention comprises a bolt transducer which can be mounted at any machine component interface which experiences cutting force loads from the machining process.
• the transducer assembly is mounted between the head of a bolt and one of the machine components secured by the bolt.
• the transducer assembly includes a force transducer, an upper shim, and a lower shim.
• the bolt preferably extends through the transducer assembly though such is not necessary. When preloaded during normal assembly of the machine components, the transducer will be able to measure increases or decreases in tensile load on the bolt caused by the machining process. The variation in bolt tensile load will be opposite in magnitude to the interface load between the two
• the transducer is able to accurately measure these variations in bolt tensile load which are representative of the cutting forces generated between the tool and workpiece.
• the very high sensitivity of piezoelectronic load cells make this transducer assembly an accurate, reliable, and effective means for measuring cutting forces.
• a primary object of the present invention is to provide a method and apparatus for monitoring tool condition which can be incorporated into existing machine tools without any modification to the machine tools.
• Another object of the present invention is to provide a method and apparatus for monitoring tool condition which can be mounted on any bolt securing any two components together which experience cutting force loads.
• a further object of the present invention is to provide a sensor assembly for monitoring tool condition that is capable of accurately measuring cutting forces
• Another object of the present invention is to provide a load sensing arrangement which will be sensitive to small changes in tensile load of a bolt.
• Still a further object of the present invention is to provide a transducer mounting
• Figure 1 is a schematic illustration of a machine tool having the transducer assembly of the present invention mounted thereon.
• Figure 2 is a schematic illustration of the transducer assembly enclosed with a protective housing.
• Figure 3 is a schematic illustration of a second arrangement for the force transducer assembly.
• Figure 4 is a schematic illustration of a third arrangement for the force transducer assembly. DETAILED DESCRIPTION OF THE INVENTION
• a machine tool is schematically shown in Fig. 1 and indicated generally by the numeral 10.
• the machine tool comprises a turret housing 12 mounted to a support member 24 by bolts 26.
• a turret disc 14 is rotatively
• Toolholder 16 is adapted to receive and hold a cutting tool 18.
• a workpiece holder 22 is disposed
• the cutting tool 18 is brought into engagement with the
• a force transducer assembly 30 is mounted on a bolt 26 securing the turret housing 12 to the support member 24.
• the force transducer assembly 30 measures the change in tensile load of the bolt 26 securing these two members together. The tensile load on the bolt 26 will vary in magnitude during the
• the variation in the tensile load on the bolt 26 will be opposite in magnitude to the cutting force load between the two machine components 12 and 24. For example, an increase in the interface load between the machine components 12 and 24 will cause a decrease in bolt tensile load, and vice versa.
• the transducer assembly monitors the variation in bolt tensile load to provide an indication of the cutting forces.
• FIG. 2 there is shown a schematic illustration of the force
• the force transducer assembly 30 includes a piezoelectric load
• the load cell 32 which is mounted in force transmitting relationship between the head of the bolt 26 and the turret housing 12. Load cell could also be placed between a nut or stop and one of the machine components.
• the load cell 32 is sandwiched between two force distributing elements.
• the force distributing elements consist of an upper shim 34 and lower shim 36.
• the load cell 32 and force-distributing elements 34 and 36 are ring-shaped and the bolt 26
• the load cell 32 will be mounted in a hostile environment on the machine. Sealing and protecting the load cell can be accomplished by enclosing the transducer assembly 30 in a water-tight housing 50 as shown in Fig. 2. Two screws 58 secure the water-tight housing 50 to the turret housing 12 in the figure. An adhesive sealant 56 can be used with the screws 58 or independently to secure the components together.
• the load cell's signal cable 48 can pass through a reinforced
• the load cell 32 can be assembled into a self-contained and sealed shim. Load cell 32 is preloaded during assembly of the machine components by tightening bolt 26 a predetermined amount. During a machining operation, variations in the cutting force will cause a corresponding increase or decrease in the cutting force loads at the interface between the two machine components. A resulting increase/decrease in the bolt's tensile load also occurs which is opposite in magnitude from that of the interface load between the two machine components. For example, an
• the highly sensitive load cell 32 is able to accurately measure the variations
• the signals produced by the load cell 32 are passed through a signal cable
• FIG. 3 a second embodiment of the present invention is shown.
• the force transducer assembly 30 includes a load cell 32 which is
• the load cell 32 is disposed closely adjacent to one side of the bolt 26, rather than surrounding the bolt 26.
• the transducer assembly 30 includes two force distributing elements. In this
• one of the force distributing elements comprises a shim 36.
• the force distributing element comprises a force transmitting lever 38.
• the force transmitting lever 38 includes a semi-circular fulcrum 40, a lever portion 44, and a through hole 42 disposed between the fulcrum 40 and the lever portion 44.
• the bolt 26 extends through the throughhole 42 and is tightened against the lever 38 so that the lever portion 44
• the force transducer assembly 30 of the second embodiment works in the same manner as in the previous embodiment.
• the load cell 32 monitors the variations in the tensile load on the bolt.
• output signal from the load cell 32 is transmitted to signal processing equipment to provide an indication of the cutting forces.
• a third embodiment of the invention is shown.
• the force transducer assembly 30 of this embodiment is designed for use with two or more
• This embodiment uses a force distributing plate 46 as a force distributing member. Bolts 26 are extended through bolt holes in the plate 46 and secure the two machine components together. A load cell 32 is disposed in force-transmitting relation between the force distributing plate 46 and one of the machine components. The bolts 26 are then tightened to preload the cell 32.
• the force transducer assembly 30 of this embodiment operates in the same manner as previously described.
• transducer assembly of the present invention can be used in virtually any machine tool without modification to the tool.
• the transducer assembly 30 simply mounts onto or in close proximity to an

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• Engineering & Computer Science (AREA)
• Human Computer Interaction (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
• Machine Tool Sensing Apparatuses (AREA)
• Force Measurement Appropriate To Specific Purposes (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=21733569

Family Applications (1)

Country Status (2)

Citations (3)

Family Cites Families (6)

• 1993
  • 1993-04-28 EP EP93910866A patent/EP0708915A4/de not_active Withdrawn
  • 1993-04-28 WO PCT/US1993/003983 patent/WO1994016302A1/en not_active Ceased

Patent Citations (3)

Non-Patent Citations (1)

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