Method Of Dressing The Grinding Wheel In A Grinding Machine

Abstract

During the dressing of a rotatable grinding disc or wheel, a feeler, which is connected to the dressing tool holder, senses the vibrations of the holder, and transforms them into electrical signals, the potential of which is proportional to the depth to which the tool penetrates the surface of the disc. These signals are used to control the cutting depth of the dressing tool, when necessary; and they may be used to effect repetition of the dressing until a signal of predetermined potential is attained.

Parent Case Text

This application is a continuation-in-part of my copending U.S. application Ser. No. 463,939, filed June 14, 1965, now U.S. Pat. No. 3,404,670, granted Oct. 8, 1968.

Description

The invention relates to a method of sharpening (dressing) the grinding wheel in a grinding machine.

More particularly this invention relates to a method of dressing a rotatable grinding disc or wheel in a grinding machine by means of a dressing tool supported by a holder and usually containing a diamond tip. This dressing has for its object to restore at even intervals the form of the grinding surface of the grinding wheel by removing dull abrasive grains from its surface, and also to restore the generatrix of the grinding wheel, which is in contact with the rotatable workpiece, to a predetermined position in the machine. After the dressing operation the grinding wheel is fed towards the workpiece until the desired final dimension is obtained on the worked surface thereof.

Either the grinding disc or the workpiece is mounted on a sliding carriage which is actuated by a feeding device to move transverse to the axis of rotation of said wheel or said workpiece. After the grinding of a workpiece has been finished the transverse sliding carriage returns to a starting position. Before the grinding wheel is subjected to a dressing treatment it is reset relative to the diamond in the transverse direction in such a manner that the diamond will cut off a predetermined layer of the grinding wheel. This complement, in the resetting of the grinding wheel, which is also denominated compensation, adjusts the grinding wheel toward the diamond, as viewed radially, to an extent which is slightly greater than the wear or abrasion which normally takes place between each dressing operation. The diamond in turn can be actuated so as to be caused to occupy an exact position within the machine as shown, for example, in the U.S. Pat. No. 3,003,293.

The wear on the grinding wheel is mainly dependent on the quantity of material ground off from each workpiece. It is difficult to maintain sufficiently narrow tolerances during the manufacture of the workpieces; and for this reason the amount of material, which must be ground off each workpiece, will vary from piece to piece. The smaller the grinding wheel, the greater will be its wear in radial dimension. The cutting depth or complement, as indicated above, normally is adjusted to a value which is slightly greater than the greatest anticipated wear, in order to avoid the risk of obtaining defective products because of a failure to dress the grinding wheel to the necessary depth. The practice has been, therefore, to adjust the wheel for a complement which normally is much too great for the majority of workpieces to be ground, with the result that there is an unnecessarily great consumption of the grinding wheel.

One main object of the invention is to provide a grinding machine having an automatic grinding cycle, wherein the dressing depth is adjusted automatically, when the wear is greater than the complement to which the machine has been adjusted.

A further object of the invention is to provide a feeling or scanning member responsive to an adjustment of the diamond holder, created by the dressing operation proper, and adapted to produce a voltage which is dependent on the magnitude of the dressing depth, and which is utilized for reading the dressing depth and/or adjustment thereof to a desired value.

A still further object of the invention is to provide a reader device which on actuation by the produced voltage shows how much the disc has been dressed off each time, i.e. to what depth material has been removed from the wheel.

According to one main object of the invention the dressing tool and grinding wheel are adjusted in relation to one another to a complement depth corresponding to an anticipated average wear between dressing intervals, and when a workpiece demanding a greater grinding allowance than normal, causes excessive wear of the disc, the dressing depth is automatically adjusted by effecting one or several repeated dressing cycles.

The invention is particularly advantageous for workpieces having small diameter holes to be ground, and which thus call for grinding wheels having small diameter. The gain achieved by the invention is not only considerable in respect to the costs for the grinding wheels, but in addition the intervals between required replacements of worn-out grinding discs are substantially increased.

In fully automatic machines the invention is of particular advantage, because it is therefore possible automatically to control the dressing operation, whereas in conventional machines the dressing operation must be controlled by expert workmen.

In the drawings:

FIG. 1 illustrates schematically one way in which the dressing of a grinding wheel may be sensed and controlled according to one embodiment of this invention; and

FIG. 2 illustrates schematically the sensing and controlling of the dressing operation in accordance with a second embodiment of this invention.

Referring now to FIG. 1, the feeler or scanning member 10 may be a vibration- or wire-elongation pickup or the like, which is engaged with a dressing tool such as a conventional diamond holder 12, so that it develops an electronic potential as the result of the vibrations of the diamond holder. The magnitude of the vibrations, and that of the potential, is proportional to the depth to which the tool 12 penetrates the surface of the grinding disc or wheel 14 during a dressing operation, and follows a curve which normally is not linear. During the dressing operation the diamond holder 12, which may have the form of an arm, is subjected to oscillations having a frequency which is characteristic of the dressing moment, and does not appear anywhere else. The oscillations correspond to the resonant frequency or the frequency of impacts of the kernels of the grinding disc against the diamond tip of the dresser. Simultaneously, disturbing frequencies, which have nothing to do with the sharpening operation proper and thus appear also when the diamond is out of operation, are filtered off. The impulses from the feeler or scanning device 10 pass through an adjustable band-pass filter 16 which may be adjusted to that frequency which produces the greatest voltage, and which is then coupled to an amplifier 18 which in turn drives a pointer-type indicating instrument 20, for example. By means of a potentiometer 22 the sensitivity can then be adjusted in every case in such a manner that full deflection is indicated on the scale 20, when dressing is unnecessarily great. The output potential from the amplifier may in addition be coupled to two current relays 24 and 25, one of them being adapted to deliver a signal when the deflections are too small and the other to deliver a signal when the deflections are too great. These impulses may in turn actuate setting members 26 and 27 of the machine for control and adjustment of the magnitude of the complement or compensation.

It is thus possible to observe during the grinding operation proper the deflections from the pointer-indicating instrument and to adjust the complement or compensation to an optimum value with reference to the degree of utilization of the grinding disc or wheel. Further it is possible to switch impulses from the maximum and minimum indicating relays to setting members which automatically reset the complement or compensation to the most favorable value thereby affording the grinding disc or wheel the longest possible life.

In the embodiment illustrated in FIG. 2, wherein like numerals are used to designate elements like those employed in the first-described embodiment, the output signal from the feeler or scanning member 10 is applied through potentiometer 31, the band-pass filter 16, and the amplifier 18 to an indicating instrument 28, which is generally similar to the instrument 20 in the first embodiment. Instrument 28 has or operates a contact 30. In this embodiment the potentiometer 31 is used to adjust the potential to be amplified by amplifier 18 in such manner that the pointer of instrument 28 is fully or almost fully deflected at all dressing depths. Undesirable frequencies are filtered out in the same manner as in the preceding embodiment by filter 16 inserted between the potentiometer 31 and the amplifier 18.

The contact 30 forms part of a circuit 32 which also includes, in series, a relay 34 and a power supply, such as for example, a battery 35. A movable contact 36, which is controlled by relay 34, energizes one or the other of two control circuits 38 and 40, depending upon the position of contact 36. These circuits contain relay contacts 38' and 40', respectively. The circuit 38, when energized, imparts to the machine controls a signal that causes the dressing operation to be repeated. When the circuit 40 is energized, dressing is terminated, and the grinding operation on the work is resumed.

The magnitude of the depth of dressing is adjustable, and according to the invention is kept small, for example, not more than a few thousandths of a millimeter, but that value normally, but not always, very narrowly exceeds the depth to which the grinding wheel has been worn over part or all of its breadth. If the signal emitted from the feeler 10 is too little, as a consequence of the dressing not having been sufficient over the entire working surface of the grinding disc, the signal to the instrument 28 is too feeble to cause the switch contact 30 to be closed. Therefore the relay coil 34 remains deenergized, and continues to hold the movable contact 36 in engagement with fixed contact 38'. This maintains the circuit 38, thus commanding the machine to perform a dressing operation, so that dressing is repeated at the same dressing depth as before. When the dressing of the grinding disc is satisfactory, the signal sent from the feeler 10 to the instrument 28 is large enough to cause contact 30 to close, so that the circuit 32 is closed. The now-energized relay 34 then moves the contact 36 away from contact 38' and into engagement with contact 40' to break circuit 38, and close circuit 40. The machine will then resume grinding.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.

Claims

Having thus described my invention, what I claim is:

1. A method of sharpening the grinding disc in a grinding machine by means of a dressing tool supported by a holder and preferably containing a diamond tip, said tool and said grinding disc prior to each grinding operation being reset in relationship to one another to a position in which a removal of disc material will take place, comprising

sensing the amplitude of the vibration of the holder created by the dressing operation,

causing the amplitude of the vibrations to produce a potential, which is dependent on the magnitude of the dressing depth, and

applying the potential to a meter for reading the dressing depth.

2. A method of dressing the grinding disc in a grinding machine by means of a dressing tool supported by a holder and preferably containing a diamond tip, said tool and said grinding disc prior to each grinding operation being reset in relationship to one another to a position in which a removal of disc material will take place, comprising

detecting, by means of a feeling member, the amplitude of the vibration of the holder created by the dressing operation,

producing a potential which is dependent on the magnitude of the dressing depth, and

adjusting the dressing depth to a desired value.

3. A method as defined in claim 2, including repeating the dressing operation until the magnitude of said potential reaches a predetermined value.

4. A method as claimed in claim 2, including repeating the dressing operation when the potential developed during a given dressing operation falls below a predetermined minimum value.

5. A method of dressing the grinding disc in a grinding machine by means of a dressing tool supported by a holder in which said tool and said grinding disc prior to each grinding operation are reset in relation to one another to a position in which removal of disc material will take place through a dressing operation, comprising

adjusting the dressing depth to a relatively small value, which is normally sufficient to restore the grinding ability of the disc,

detecting, by means of a feeling member, the amplitude of the vibration of the holder created in the dressing operation by the mechanical resistance of the grinding disc to movement of the tool across the disc,

producing a potential, which is dependent on the vibration of the holder, and, if necessary,

repeating the dressing operation until the potential reaches a predetermined value.