US3250043A - Fail-safe speed control system for abrasive wheels - Google Patents

Description

May 10, 1966 A, W, FINKL 3,250,043

FAILVSAFE SPEED CONTROL SYSTEM FOR ABRASIVE WHEELS May 10, 1966 A. W. FINKL.

Filed Aug. 27, 1963 FAIL SAFE SPEED CONTROL SYSTEM FOR ABRASIVE WHEELS 2 Sheets-Sheet 2 daf INVENTOR.

United States Patent O 3,250,043 FAIL-SAFE SPEED CONTROL SYSTEM FOR ABRASIVE WHEELS Anthony W. Finkl, Chicago, Ill., assignor to A. Fink] & Sons Co., Chicago, Ill., a corporation of Illinois Filed Aug. 27, 1963, Ser. No. 304,810 5 Claims. (Cl. 51-134.5)

' This application is a continuation-in-part of my copending application Serial No. 282,640, filed-'May 23, 1963.

This invention relates generally to the control of the peripheral speed of a rapidly rotating member. Specifically, it-relates to a system for controlling the peripheral speed of a large abrasive cut-off wheel or disc whereby maximum cutting efficiency is substantially tmaintained over the entire wheel speed range. In other words, the peripheral speed of the abrasive wheel is maintained close to the maximum safe peripheral Wheel speed as the wheel diameter decreases from wear, and the wheel r.p.m. correspondingly increases. t

Accordingly, a primary object of my invention is to provide a control system for large abrasive cut-off wheels or discs.

Another object is to provide such ya control Asystem which maintains the peripheral speed of the wheel close to, or within, a predetermined maximum safe peripheral speed range as the wheel r.p.m. is increased due to wheel wear.

A further object is to provide a control system for an abrasive cut-off wheel or disc in which the r.p.m. of the wheel is automatically increased upon Wear of the wheel to a predetermined point, the increased r.p.m. resulting in a peripheral speed close to or within the maximum Vsafe peripheral speed.

4for maintaining the peripheral speed of an abrasive wheel at or below a predetermined speed limit or range which does not require physical contact with the wheel or any related parts of the entire assembly to sense, and control, the wheel speed.

Yet a further object is to provide `a control system for an abrasive wheel or disc which uses a beam of energy, either visible or invisible, to regulate the wheel speed, the beam signal being controlled by the physical sizeof the wheel itself.

Yet another object is to provide a control system in which the speed of the Wheel is automatically controlled without the exercise of any discretion by the operator or the necessity of making physical adjustments by the operator during the useful life of the wheel.

Other objects and advantages of the invention will become apparent from a reading of the following detailed description of a preferred embodiment of the invention.

My invention in the broadest form comprises a system for controlling the peripheral speed of a rotating wheel without physically contacting the wheel or any related parts of the entire assembly. I am aware of prior art attempts to control, and maintain, within predetermined limits, the peripheral speed of an `abrasive wheel, but to my knowledge they all involve some form of physical contact with the wheel or parts of the structure, either direct or indirect.

In my co-pending application Serial No. 282,640, filed May 23, 1963, of which this application is a continua- ICC tion-in-part, I disclose a system for controlling the peripheral speed of an abrasive wheel by changing the Wheel housing which involves, in effect, indirect physical contact with the wheel.

My present system controls the speed of rotation by sensing the physical size of the wheel from a point remote therefrom and thereafter suitably controlling the peripheral speed of the wheel in response to the sensed size of the wheel. In my preferred embodiment, which is disclosed in the accompanying drawing and explained in detail in the following description, a source of visible or invisible light or other forms of directable energy is so positioned that its path will be interrupted by the physical presence of the wheel, and, so long as its path is interrupted, suitable energy activated controls are not able to operate to increase the Wheel r.p.m. In addition to visible and invisible light, such as 'infra-red and ultraviolet, beta and gamma rays may be employed in conjunction with suitable means for responding to the signals generated by the absence or presence of these latter signal generating sources.

Common to all of the above described systems is the fact that there is no physical Contact, either direct or indirect, between the Wheel size and speed measuring and activating mechanism and the wheel itself.

The preferred embodiment of the invention is illustrated more or less diagrammatically in the accompanying figures wherein:

FIGURE 1 is a schematic view of my control system;

FIGURE 2 is a detailed view of a portion of my control system; and

FIGURE 3 is a wiring diagram of a preferred embodiment of my invention.

Like reference numerals will be used to refer-to like or similar parts in the following description of the drawmgs.

A wheel or other rotating memberl whose peripheral speed is to be controlled is indicated at 10 in FIGURE 1. My control system is applicable to a Wide variety of rotat-ing members but for convenience of description and illustration I will describe my invention in connection with a large abrasive cut-off wheel or disc. The origin-al size of tthe wheel is indicated at 11. The decrease 4in diameter of the wheel is due to wear, and the solid line outline of the wheel represents the condition of the wheel at that point in its life span at which my control system functions to increase the r.p.m.

The wheel is mounted on a shaft 12 by any suitable means 13. The shaft carries a pulley 14 which is connected by a belt or other power transmission'member 15 to a drive pulley 16 mounted on the power shaft 17 of an electric motor 18. .The electric motor is amultiple speed motor. For convenience of description a two-speed motor is illustrated and described.

The cut-olf wheel rotates in a Wheel guard or housing indicated generally at 20 which may be bolted or otherwise permanently secured to the machine frame 21. A pair of apertures 22 and 23 are formed in the opposite side walls of the housing. Means for generating a beam of energy is indicated at 24. The means may be a source of visible light or alternatively, and preferably, a source of invisible light lsuch as -a source of infra-red light.

Means for generating an electric current in 4response to reception of a beam of energy from source 24 is indicated at 25. The generating -means is preferably a photoelectric cell which functions in a well-known manner to generate a signal current vupon reception of `a `beam of visible or invisible light.

The signal current generated by the photo-electric cell 25 is transmitted to power amplifier 26 which is connected to any suitable power source, preferably a source of l10- volt alternating current. The power ampliiier in turn is 11G-volt alternating current power source.

connected to a fail-safe control circuit for varying the motor speed, the circuit being indicated generally at 27. Three lines, 28, 29 and 30 extend from the control circuit to the two-speed motor 18. One of the lines is a common and the other two lines are associated with -a set of windings in the motor field, one of the windings being associated with a low-speed circuit and the other winding with a high-speed circuit in a manner well known in the art.

The abrasive wheel and its associated housing is shown in detail in FIGURE 2. Each of apertures 22 and 23 is a hole, slot or other aperture whose sides diverge upwardly and outwardly from the center of the housing. The taper of the light aperture aids in preventing entrapment of dirt and particles worn away from `the wheel and workpiece. A deector which may, for example, be'a shallow cone or dome-s-haped piece of sheet metal which has an 'aperture 35 at its apex aligned w-ith the light path extends between the housing apertures 22 and 23. Bolts 36 or other suitable securing means connect each deiiector by its peripheral lange 37 to the housing wall. The lower portion of the `deflector is spaced outwardly from the housing wall by `a spacer 38. The spacer permits the abrasive dust to fall through, thereby preventing the accumulation of dust build-up.

A pair of transparent safety covers for the source and pick up of energy are indicated at 40 and `41. Preferably a shatterproof glass or cle-ar plastic is employed. Each glass is removably mounted on the outside of the wall housing by `a pair of-mounting flanges 42. Each plate or safety cover prevents the escape of grinding dust without interfering with the transmission of alight beam from one side of the housing to the other. Cover 40 further prevents the photo-electric cell or eye from becoming pitted and eroded from the high speed particles that iiy off the abrasive wheel during engagement with a workpiece. Pitting and erosion of the wheel would ultimately cause loss of light transmission to the photo-electric cell, thereby preventing eiiicient functioning of the system. Should this ever happen, the system will run at low speed as will later be explained in detail.

The speed control circuit for the motor 18 is shown in detail in FIGURE 3. Lines L1 and L2 terminate at a A safety fuse 44 and olf-on switch 45 are located in L1. The motor 18 is connected across main power lines L1 -and L2 by a pair of lines 30 and 46. Line 46 terminates at a speed switch 47 which is normally biased into contact with contact 48 in line 28. Line 29 terminates in a contact 49. The unotor will operate at high or low speed depending upon which contact speed switch 47 is in operation.

The source of energy, in lthis instance a source of visible light 24, is connected directly across lines 46 and 30 and will therefore be on whenever the off-on switch 45 is closed.

Photo-electric cell 25, which is positioned to pick up the beam of energy from source 24, is connected to power arnplitier 26 by a pair of leads 50 yand 51. The power ampliiier in turn is connected across the line voltage by leads 52 and 53. The output leads 54, 55 from the power ampliiier are connected to the ends of a sensitive solenoid coil 56, the coil 56 controlling normally open switch 57. The contact side of switch 57 is connected by a line 58 through the secondary winding 59 of a low voltage circuit control transformer Y60, the primary winding of which is connected across power lines L1 and L2. The other side of the secondary coil 59 is connected by line 61 to one end of another solenoid coil 62. The other end of solenoid coil 62 is connected to switch 57 by line 63. Solenoid 62 controls speed switch 47 which is normally biased into contact with the low lspeed circuit contact 48.

The use and operation of my invention is as follows:

Grinding wheelsv have an optimum peripheral speed, or at least an optimum peripheral speed range, within which the grinding or cutting action of the wheel is most eifective and it is highly desirable that the wheel be operated at or close to that operationg speed at all times. As a practical matter, it is impossible to maintain the peripheral speed of the wheel at the optimum speed or speed range if the wheel r.p.m. ismaintained constant. This is because the diameter of the wheel wears down with use, particularly where the wheel is employed primairily as a cutting tool, such as an abrasive cut-off wheel. As the wheel wears the peripheral speed decreases and optimum cutting efficiency falls off. This problem is especially acute with thin wheels which wear rather quickly, such as those used for cut-olf yof steel or other high strength metals.

The problem of maintenance of an optimum peripheral wheel speed can be cured by increasing the rpm. of the wheel as the diameter decreases from wear. In the prior art this has generally been done by increasing the speed of the wheel motor, although other schemes such as varying the size of drive pulleys between the vmotor and the wheel also have been employed.

Equipping a grinding wheel with a multiple or variable speed motor has serious drawbacks, however. If, for example, a new maxi-mum diameter wheel is placed on a spindle and the wheel rotated at the trate of speed intended to be used with a wheel of smaller diameter, the wheel could physically break up. Centrifugal explosion resulting in injury to the operator and damage to the equipment could easily occur. This is a constant danger because it is entirely possible for an operator to remove a worn, small diameter wheel, which has 'been turned at a maximum r.p.m., and install a new, maximum diameter Wheel, and forget to correct the motor speed to compensate for the diiierence in wheel diameter. If the motor is then started with the new maximum diameter wheel in place, with the motor speed setting intended for a minimum diameter wheel, it is entirely possible for the wheel to explode causing serious danger to the operator and the machine.

My invention provides automatic control of the peripheral speed of the wheel, all the while maintaining the peripheral speed at or near the proper speed for optimum cutting eiiiciency.

Further, it is impossible for the wheel, when equipped with my invention, to be operated at too high a speed because the high speed motor circuit cannot be energized until the wheel has worn away to a point at which an increase in r.p.m. will not increase the peripheral speed of the wheel past a pre-determined safe maximum operating limit. In addition, failure of any component in the control system will result either in shut-down of the system gr cutback of the operating speed to the lowest motor spee Referring now to FIGURE 3, and assuming an abrasive cutting wheel of a size indicated at 11 in FIGURE l is installed on wheel shaft 12, closure of the off-0n switch 45 will result in operation of the two-speed motor 18 at its low speed. The motor is energized through lines 30 and 46, line 46 terminating in speed switch 47 which is in contact with contact 48 in the low speed circuit 28 of the motor. The source of energy 24 is likewise energized as itis connected directly across lines 46 and 30.

The beam of energy, preferably invisible light emanating from source 24, will pass through aperture 23 in the right wall of housing 20. So long as the grinding wheel blocks the path of light between apertures 23 and 22 in the housing walls, no signal will be received by the photo-electric cell 25. As soon as the wheel wears to a diameter indicated in FIGURE 3'however, the photoelectric cell will be energized since the light path between apertures 22 and 23 will be uncovered by the wheel. At this time the peripheral speed of the wheel will be considerably less than it was originally even though the r.p.m. is constant. If the original peripheral speed of the wheel was close to or within the safe operating speed, the peripheral speed of the wheel in its FIGURE 3 condition will be somewhat below the safe, optimum operating speed.

The signal generated by the photo-electric cell 25 is transmitted to power amplifier 26 by the appropriate lead 50 or 51. The power amplifier will immediately amplify the signal which is then transmitted to solenoid coil 56. Normally open contact 57 will immediately close. Closure of contact 57 energizes solenoid coil 62 since coil 62 is connected directly to the output winding of transformer 60 by lines 63, 58 and 61. Energization of solenoid coil 62 moves speed switch 47 from its illustrated position into contact with high speed contact 49. Movement of the switch opens the low speed circuit and energizes the high lspeed circuit. The motor speed is immediately increased which results in an increase in r.p.m. and consequently the peripheral speed of the grin-ding wheel 10. f

Should any failure occur in any ycomponent of the system other than lines 28, 29, 30 and speed switch 47 and its associated contacts 48, 49, the motor speed will immediately drop to low, and the grinding wheel will slow up. Thus, for example, should light 24 burn out, the photo-electric cell 25 will not generate any signal to the power amplifier and coil 56 will be de-energized. The de-energization of coil 56 will open switch 57 and deenergize coil 62 and the speed switch will return to its normal position in contact with low speed contact 48.

Although a preferred embodiment of the invention has been illustrated and several Variations have been specifically described, it will at once be apparent to those skilled in the art that further changes may be made Without departing from the spirit of my invention. Accordingly, it

is my intention that my invention be limited not by the foregoing exemplary description but solely by the s-cope of the hereafter appended claims considered in view of the pertinent prior art.

I claim:

-1. A fail-safe control system for large abrasive cut-olf wheels or discs which are powered by a motor having a high speed contact and a low speed contact, said system including, in combination,

a low speed circuit connecting the low speed contact of the motor to asource of power,

:said low speed circuit having a speed switch therein which is normally biased to complete the circuit,

a high speed circuit connecting the high speed cont-act of the motor to the speed switch when the speed switch is biased to a position in which the high speed circuit is completed, and the low speed circuit is opened, and

means for completing the high speed circuit to thereby increase the r.p.m. of the abrasive wheel upon wear of the wheel to a predetermined diameter smaller than the original diameter,

said means including an energy source which generates an axially directed beam of energy, of substantially constant diameter at any convenient distance from the wheel,

a photo-electric cell energizable upon the reception of the beam of energy,

said energy source and photo-electric cell flanking the abrasive wheel and being so positioned with respect to one another that the wheel will prevent reception of the beam by the photo electric cell until the wheel has worn to a diameter such that the peripheral speed of the wheel when rotated at high speed will be Within a pre-determined maximum safe speed,

a power amplifier connected to a source of power and to the photo-electric cell,

coil means connected to the power amplifier and associated with the speed switch,

, ously decrease in size as it works, said system including,

in combination,

first circuit means effective, when energized, to operate :said multi-speed motor at a low speed,

second circuit means effective, when energized, to op crate said motor at a higher speed,

means for generating and receiving an axially directed beam of energy of substantially constant width,

said means for generating the beam of energy and the means for receiving it, being located outside a wheel guard,

the wheel guard having apertures which enable the beam, in the absence of the wheel or disc to pass therethrough, l

the wheel guard apertures being inclined toward the taxis of rotation of the wheel, and inwardly toward one another, to thereby reduce entrapment of dust,

said wheel or disc being so positioned so as to interrupt the beam until the wheel or disc wears a pre-determined amount, and

means for energizing the second circuit means upon reception of the axially directed beam of energy by a receiver associated with the second circuit means.

3. The system of claim 2 further characterized in that at least one of the apertures has an interiorly positioned dust deilector guard carried by an associated Wall of the wheel guard, at least the lower portion of the defiector guard being spaced away from the wall to thereby enable dust to fall through whereby dust build-up is prevented.

4. A system for varying, in discontinuous increments, the speed of rotation of a multi-speed motor which drives an abrasive wheel or disc, which wheel or disc continuously decreases in size as it works, said system including, in combination,

first circuit means effective, when energized, to operate said multi-speedmotor at a low speed,

second circuit means effective, when energized, to operate said motor at a higher speed,

means for generating an axially directed beam of energy of substantially constant width,

means for receiving said axially directed 'beam of energy,

-said wheel or disc being so positioned as to interrupt the aforesaid beam until the wheel'or disc wears a predetermined amount,

means for translating the received axially directed beam of energy into a control signal, and

means for energizing the second circuit means and deenergizing the first circuit means upon reception of the control signal derived from the axially directed beam of energy.

5. The system of claim 4 further characterized in that the means for generating the beam is a source of visible light.

References Cited by the Examiner UNITED lSTATES PATENTS 766,229 8/ 1904 Douglas 51--134-.5 2,994,994 8/ 19611 Lonaberger 51-1345 3,113,405 12/196-3 Schneider et al. 51-134.5

LESTER M. SWINGLE, Primary Examiner,

I. SPENCER OVERHOLSER, Examiner.

J. L. TATE, Assistant Examiner.

Claims (1)

1. A FAIL-SAFE CONTROL SYSTEM FOR LARGE ABRASIVE CUT-OFF WHEELS OR DISCS WHICH ARE POWERED BY A MOTOR HAVING A HIGH SPEED CONTACT AND A LOW SPEED CONTACT, SAID SYSTEM INCLUDING, IN COMBINATION, A LOW SPEED CIRCUIT CONNECTING THE LOW SPEED CONTACT OF THE MOTOR TO A SOURCE OF POWER, SAID LOW SPEED CIRCUIT HAVING A SPEED SWITCH THEREIN WHICH IS NORMALLY BIASED TO COMPLEWTE THE CIRCUIT, A HIGH SPEED CIRCUIT CONNECTING THE HIGH SPEED CONTACT OF THE MOTOR TO THE SPEED SWITCH WHEN THE SPEED SWITCH IS BIASED TO A POSITION IN WHICH THE HIGH SPEED CIRCUIT IS COMPLETED, AND THE LOW SPEED CIRCUIT IS OPENED, AND MEANS FOR COMPLETING THE HIGH SPEED CIRCUIT TO THEREBY INCREASE THE R.P.M. OF THE ABRASIVE WHEEL UPON WEAR OF THE WHEEL TO A PREDETERMINED DIAMETER SMALLER THAN THE ORGINAL DIAMETER, SAID MEANS INCLUDING AN ENERGY SOURCE WHICH GENERATES AN AXIALLY DIRECTED BEAM OF ENERGY, OF SUBSTANTIALLY CONSTANT DIAMETER AT ANY CONVENIENT DISTANCE FROM THE WHEEL, A PHOTO-ELECTRIC CELL ENERGIZABLE UPON THE RECEPTION OF THE BEAM OF ENERGY, SAID ENERGY SOURCE AND PHOTO-ELECTRIC CELL FLANKING THE ABRASIVE WHEEL AND BEING SO POSITIONED WITH RESPECT TO ONE ANOTHER THAT THE WHEEL WILL PREVENT RECEPTION OF THE BEAM BY THE PHOTO ELECTRIC CELL UNTIL THE WHEEL HAS WORN TO A DIAMETER SUCH THAT THE PERIPHERY SPEED OF THE WHEEL WHEN ROTATED AT HIGH SPEED WILL BE WITHIN A PRE-DETERMINED MAXIMUM SAFE SPEED, A POWER AMPLIFIER CONNECTED TO A SOURCE OF POWER AND TO THE PHOTO-ELECTRIC CELL, COIL MEANS CONNECTED TO THE POWER AMPLIFIER AND ASSOCIATED WITH THE SPEED SWITCH, SAID COIL MEANS, WHEN ENERGIZED BY A SIGNAL FROM THE POWER AMPLIFIER, BEING OPERABLE TO BIAS THE SPEED SWITCH TO A POSITION IN WHICH IS COMPLETES THE HIGH SPEED CIRCUIT, AND OPENS THE LOW SPEED CIRCUIT.

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