Milling machine control system and milling force sensor therefor

Claim 2

A force sensor which converts deflection of a milling machine spindle into a proportional milling force signal for use with a feedrate control system responsive thereto, including: a. first and second magnetic transducer means, each transducer means including a winding, b. means supporting said first and second transducer means in proximity to the circumference of the spindle but opposed along a diameter thereof, c. an alternating current source coupled to said windings, d. means connecting said windings in opposition, whereby a common output signal thereof includes a component having a frequency equal to that of said AC source which is amplitude modulated in accordance with the relative deflection of the spindle along said diameter, and e. a demodulating means converting said amplitude modulated component into a DC milling force signal.

Claim 3

A sensor as recited in claim 1 wherein said demodulating means comprises: a. a differential amplifier having said common output signal connected thereto, b. a band-pass filter means removing from the output of said differential amplifier components thereof which have a frequency other than that of said AC source, and c. a demodulator circuit extracting said amplitude-modulated component and producing therefrom said DC milling force signal.

Claim 4

A sensor as recited in claim 2 wherein said demodulator circuit comprises means rectifying a half cycle of said amplitude-modulated component and means filtering said rectified, amplitude-modulated component, and wherein said demodulating means further comprises an amplifier interposed between said band-pass filter and said demodulator circuit.

Claim 5

A force sensor as recited in claim 1 further comprising: a. third and fourth magnetic transducer means, each including a winding, b. means supporting said third and fourth transducer means in proximity to the circumference of the spindle but opposed along a second diameter thereof which is perpendicular to said first diameter, c. said AC source being coupled to said windings of said third and fourth transducers, d. means connecting said windings of said third and fourth transducer means in opposition whereby a common output signal is provided therefrom, e. a second demodulating means having a second common output signal connected thereto and producing therefrom a second DC milling force signal, and f. means summing said first and second DC milling force signals to produce a common DC milling force signal.

Claim 6

A sensor as recited in claim 4 wherein said demodulating means comprises: a. a differential amplifier having said common output signal connected thereto, b. a band-pass filter means removing from the output of said differential amplifier components thereof which have a frequency Other than that of said AC source, and c. a demodulator circuit extracting said amplitude-modulated component and producing therefrom said DC milling force signal.

Claim 7

A sensor as recited in claim 5 wherein the said demodulator circuit comprises means rectifying a half cycle of said amplitude-modulated component and means filtering said rectified, amplitude-modulated component, and wherein said demodulating means further comprises an amplifier interposed between said band-pass filter and said demodulator circuit.

Claim 8

A force sensor as recited in claim 6 wherein said summing means comprises a nonlinear circuit giving increased sensitivity for small amounts of milling force.

Claim 9

A force sensor as recited in claim 4, as modified to additionally monitor deflection of the machine spindle along its axis where the spindle includes a relatively enlarged portion comprising: a. fifth and sixth magnetic transducer means, each including a winding, b. means supporting said fifth and sixth transducer means in proximity to the relatively enlarged spindle portion and disposed along a line parallel to the axis, c. means coupling said windings of said fifth and sixth transducer means to said AC source, and means connecting said windings thereof in opposition to provide a common output signal therefrom which includes a component having a frequency equal to that of said AC source which is amplitude modulated in accordance with the relative deflection of the spindle along said parallel line, d. a third demodulating means converting the amplitude modulated component of said common output signal into a third DC milling force signal, and e. means coupling said third DC milling force signal to said summing means.

Claim 10

In a system for use with a numerically controlled milling machine including a rotatable spindle and a numerical control unit including apparatus for receiving a preprogrammed tape defining the details of a milling process, one of the details being a preset feedrate and a feedrate override means controllable to reduce the feedrate below the preset value which comprises a sensor means measuring spindle deflection and producing therefrom a signal proportional to milling force exerted on the cutting element held by the spindle during the milling process, a means providing a reference force signal, means summing the reference force signal with the milling force signal to provide an error signal equal to the difference therebetween, and a controller means which produces a control signal from the error signal when the milling force signal exceeds the reference force signal, the control signal being coupled to the feedrate override means to reduce the feedrate in proportion thereto, an improvement in the force sensor comprising: a. a plurality of magnetic transducers disposed about the periphery of the machine spindle, b. a source of exciting voltage coupled to said plurality of magnetic transducers, c. means connecting said transducers in an AC bridge which provides a common output signal including an amplitude modulated component proportional to the deflection of the spindle from a normally centered position, and d. means demodulating the common output signal to produce a milling force signal therefrom.

Claim 11

In a system for use with a numerically controlled milling machine including a rotatable spindle and a numerical control unit including apparatus for receiving a preprogrammed tape defining the details of a milling process, one of the details being a preset feedrate and a feedrate override means controllable to reduce the feedrate below the preset value which comprises a sensor means measuring spindle deflection and producing therefrom a signal proportional to milling force exerted on the cutting element held by the spindle during the milling process, a means providing a reference force signal, means summing the reference force signal with the milling force signal to provide an error signal equal to the difference therebetween, and a controller means which produces a control signal from the error signal when the milling force signal exceeds the reference force signal, the control signal being coupled to the feedrate override means to reduce the feedrate in proportion thereto, an improvement in the force sensor comprising: a. a plurality of magnetic transducers disposed about the periphery of the machine spindle, b. a source of exciting voltage coupled to said plurality of magnetic transducers, c. means connecting said transducers in an AC bridge which provides a common output signal including an amplitude modulated component proportional to the deflection of the spindle from a normally centered position, and d. means demodulating the common output signal to produce a milling force signal therefrom.

Claim 12

In a system for use with a numerically controlled milling machine including a rotatable spindle and a numerical control unit including apparatus for receiving a preprogrammed tape defining the details of a milling process, one of the details being a preset feedrate and a feedrate override means controllable to reduce the feedrate below the preset value which comprises a sensor means measuring spindle deflection and producing therefrom a signal proportional to milling force exerted on the cutting element held by the spindle during the milling process, a means providing a reference force signal, means summing the reference force signal with the milling force signal to provide an error signal equal to the difference therebetwEen, and a controller means which produces a control signal from the error signal when the milling force signal exceeds the reference force signal, the control signal being coupled to the feedrate override means to reduce the feedrate in proportion thereto, an improved controller comprising: a. a control unit operating on the error signal with a predetermined control function to produce a DC control signal therefrom, b. a comparator means having said milling force signal connected thereto and providing an output signal when said signal exceeds a predetermined threshold value, c. means rectifying said DC control signal, d. a differential amplifier having said rectified DC control signal and said output signal from said comparator means connected thereto, the output of said differential amplifier being coupled to the feedrate override circuit as a feedrate control signal, and the magnitude of said output signal being chosen to reduce feedrate to a predetermined value less than the preset value.

Claim 13

In a system for use with a numerically controlled milling machine including a rotatable spindle and a numerical control unit including apparatus for receiving a preprogrammed tape defining the details of a milling process, one of the details being a preset feedrate and a feedrate override means controllable to reduce the feedrate below the preset value which comprises a sensor means measuring spindle deflection and producing therefrom a signal proportional to milling force exerted on the cutting element held by the spindle during the milling process, a means providing a reference force signal, means summing the reference force signal with the milling force signal to provide an error signal equal to the difference therebetwEen, and a controller means which produces a control signal from the error signal when the milling force signal exceeds the reference force signal, the control signal being coupled to the feedrate override means to reduce the feedrate in proportion thereto, an improved controller comprising: a. a control unit operating on the error signal with a predetermined control function to produce a DC control signal therefrom, b. a comparator means having said milling force signal connected thereto and providing an output signal when said signal exceeds a predetermined threshold value, c. means rectifying said DC control signal, d. a differential amplifier having said rectified DC control signal and said output signal from said comparator means connected thereto, the output of said differential amplifier being coupled to the feedrate override circuit as a feedrate control signal, and the magnitude of said output signal being chosen to reduce feedrate to a predetermined value less than the preset value.