US3212218A - Levelling system for bowling lane sanding machine - Google Patents

Description

Oct. 19, 1965 D. c. sAMs ETAL LEVELLING SYSTEM FOR BOWLING LANE SANDING MACHINE Filed July 5, 1962 5 Sheets-Sheet 1 INVENTOR DAVID C. SAMS RICHARD D. WALSH 5 Sheets-Sheet 2 INVENTOR DAVID C. SAMS BY RICHARD D. WALSH Oct. 19, 1965 D. c. SAMS ETAL LEVELLING SYSTEM FOR BOWLING LANE SANDING MACHINE Filed July 5, 1962 Flegz Oct. 19, 1965 c. s s ETAL 3,212,218

LEVELLING SYSTEM FOR BOWLING LANE SANDING MACHINE Filed July 5, 1962 5 Sheets-Sheet 3 INVENTOR DAVID C. SAMS BY RICHARD D. WALSH Oct. 19, 1965 D. c. sAMs ETAL LEVELLING SYSTEM FOR BOWLING LANE SANDING MACHINE Filed July 5, 1962 5 Sheets-Sheet 4 INVENTOR DAVID C. SAMS RICHARD D. WALSH Q. 21%

Oct. 19, 1965 D. c. SAMS ETAL 3,212,218

LEVELLING SYSTEM FOR BOWLING LANE SANDING MACHINE Filed July 5, 1962 FIG. 6

5 Sheets-Sheet 5 FIG. 7

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CR2b TO LEFT TO RIGHT MOTION MOTlON INVENTOR DAVID C. SAMS B RICHARD D. WALSH United States Patent O LEVELLHNG SYSTEM FOR BOWLING LANE SANDING MACHINE David C. Sams, Plymouth, and Richard D. Walsh, Shelby,

Ohio, assignors to American Machine & Foundry Company, a corporation of New Jersey Filed July 5, 1962, Ser. No. 207,501 6 Claims. (Cl. 51--174) This invention relates to sanding machines, and more particularly to the automatic levelling of machines of the type used where perfectly horizontal sanding is a critical requirement.

The invention will be described in its application to a machine for sanding bowling lanes, because it is in such sanding that uniformity in a horizontal plane perhaps reaches its greatest imporatnce. However, the invention is also applicable to other surface finishing operations of a similar nature. In the sport of bowling, the surface condition of a lane is a highly significant factor entering into movement of a ball toward the target area. In order to be approved for official play by the various bowling associations, one requirement that is imposed is that each lane must be level from side to side within close tolerances. Bowling lanes periodically must be given a complete refinishing and in the sanding operation it obviously is desirable to maintain a levelling control over the machine in order that trueness of the lanes will be maintained. Otherwise, the errors produced by uneven sanding can become cumulative until finally a lane deviates considerably from a horizontal plane.

One approach to levelling control has been to provide means which sense the degree of trueness of the lane and to regulate the cutting action accordingly. As a sanding machine proceeds along the lane it is necessary to detect even slight deviations from level and responsively to effect the necessary corrective adjustments as quickly as pos sible. Highly satisfactory sanding of a lane can be accomplished only by the early detection of very small deviations and, ideally, by the continuous initiation of correspondingly small corrective adjustments. To this end the level sensing means must, among other requirements, be highly sensitive and accurate.

Accordingly, the main object of the invention is to provide improved sensing means, in the nature of a clinometer, of the type described. In accordance with the invention the improved sensing means as a unit is highly sensitive and accurate and in this and other respects is highly satisfactory for the control of a machine for sanding a bowling lane or other floor surface. Briefly, in accordance with the invention a bubble type liquid level system is employed in conjunction with a novel electronic control circuit. Specially, two levels in the form of vials, each containing an electrically conductive liquid, incorporate electrical contacts or electrodes which produce different effects in response to conditions of levelling. One of the vials reacts upon a very slight deviation away from a horizontal reference in one direction and the other vial reacts upon a slight deviation away from a horizontal reference in the other direction. In the preferred embodiment of the invention, each vial is coupled to its own independently operating circuit, each circuit being operative to initiate a given corrective levelling adjustment. When either of these circuits reacts to its associated levelling vial unit it produces an output of pulses which drive one of two electromagnetic devices. Each of these devices is operable to effect a levelling adjustment in a given direction. Certain advantages inhere in this pulse type of operation. Further details of the invention, however, will be more readily understood from the detailed description provided hereafter.

Other objects and advantages also will appear from the following description, read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevation of an entire bowling lane sanding machine in which the present invention is embodied;

FIGURE 2 is a partial plan view of the sanding roller assembly;

FIGURE 3 is a side elevation of the structure taken as indicated by lines 3-3 in FIGURE 2;

FIGURE 4 is a sectional side elevation taken as indicated by lines 4-4 in FIGURE 2;

FIGURE 5 is a sectional end elevation taken as indicated by lines 55 in FIGURE 4;

FIGURE 6 is a schematic illustration of the bubble type liquid levels and their associated electrodes; and

FIGURE 7 is a wiring diagram of the electrical control circuit in accordance with the invention.

FIGURES 1 and 2 present top and side views of an entire sanding machine, although as previously indicated this invention concerns principally the automatic levelling of certain machine partsthe sanding pressure drum in the instant caseto maintain trueness of a bowling lane or other floor surface. in the particular machine illustrated three drums are involved, namely, a driving drum 2, a cutting or pressure drum 4 and an idler drum 6. A suitable endless abrasive belt 8 of a width sufficient to cover the full width of a bowling lane (typically 4' to 42 inches) is trained about these drums and is rotated in a clockwise direction (in FIGURE 1) by means referred to hereafter. It is to be noted that this sanding machine is of the type wherein the sanding belt travels in align ment with the length of the bowling lane as distinguished from travel at a right angle to the lane.

The machine frame consists essentially of two parts. Forwardly, the machine frame is a weldment comprising spaced side members it] and 12 spanned by cross members 14 and 16. At the left-hand side of the machine the member 12 is detachably connected to the front cross member 18 by a pivotally connected plate 20 which is secured to the member 12 by special intermeshing elements (not shown) and a thumb screw 22. The rearward machine frame is a weldment comprising spaced side members 24 spanned by cross members 34, 36 and 38. The left-hand side frame members 12 and 28 are detachably connected by a plate 36 and thumb screws 32 The purpose of these detachable connections is, that by removing rearward plate 30 and swinging away forward plate 2%) the side frame is broken at these locations to permit sanding belts to he slipped on and off the drums 2, 4 and 6. In the course of this operation the forward portion of the sanding machine is raised above the lane or other floor surface (by means described hereafter) and to prevent the dropping of the then broken left-hand side there is incorporated a feature which is described in the copending application of John Zuercher, Serial No. 207,503 filed July 5, 1962, now Patent No. 3,123,944 and entitled Frame Structure for Sanding Machine. Briefly, this feature involves a torque bar principle whereby the right-hand side of the frame acts to maintain suspension of the broken away left-hand side of the frame. As disclosed in said copending application, to which reference may be made, in practice this is effected by coaction between an arm 26 and the forward cross member 36 of the rearward machine frame.

The forward machine frame is cantilevered outwardly from the rearward machine frame, the raising and lowering of the forward machine frame relative to the bowling lane or other floor surface being effective to vary the cutting pressure. The rearward machine frame is supported partly by heavy wheels 40 which are keyed to a transverse axle 42 driven by an electric motor 44 through a gear reduction unit 46, and which also serve to drive the sanding machine along the bowling lane or other floor surface. The remaining support for the sanding machine is provided by caster wheels 48 pivotally carried by a lead screw 50 which is axially adjustable by its rotation within a stationary nut assembly 52. A frame 56 extending upwardly provides handle bars and a support for the machine operators controls. The lead screw 50 is rotated to raise and lower the rear of the machine relative to the caster wheels 48, thereby to raise and lower the cantilevered forward pressure drum 4 by rotation about the axis of axle 42. Lead screw 50 is rotated by means of a universal drive shaft 54 which is manually operated by a handwheel 58. It will be understood that by the operation of handwheel 58 the pressure drum 4 may be raised completely above the floor surface (e.g. for the purpose of changing sanding belt 3) or on the other hand may be lowered to apply light or heavy pressure to the floor surface being sanded.

In the course of movement of the sanding machine along a bowling lane the machine is maintained in paral lel, centered relation to the lane by rollers 59 which ride along the division boards or other structure separating adjacent bowling lanes.

The finish which is removed from the floor surface in the form of dust is delivered to a closed dust container 60 by centrifugal blowers 62 which are connected to a collector duct 66 by ducts 68. A fire extinguishing system is provided which is the subject matter of the copending application of Arthur B. Viescas, Serial No. 207,504, filed July 5, 1962, now Patent No. 3,146,558 and entitled Fire Extinguishing System for Sanding Machine. Briefly, this system comprises a tank 72 containing an approved fire extinguishing agent (such as carbon dioxide) which is connected by a line 74 to the intake duct 76 of the dust container 60. A valve 75 is operated to admit the fire extinguishing agent to the dust container 60 in response to a signal emitted by means (not shown) responsive to the temperature condition within the dust container.

The driving drum 2 is rotatably supported in bearings 78 and 8d at the side frame members and 12, respectively. An electric motor 82 is mounted on a subframe assembly comprising cross members 83 and side members 24. Motor 82 drives a disk type clutch 86 through a belt drive 84, the clutch 86 being engageable to drive an output shaft 88 which in turn is connected to the drum 2 by a belt drive 90. The engagement and disengagement of clutch 86 is effected through operation of a lever 92 by a control lever 94 at the machine operators position. Motor 82 also drives the previously mentioned centrifugal blowers through a belt drive 96.

Idler drum 6 is rotatably mounted at its left end by a bearing 102, and at its right end by an assembly generally designated 104. Assembly 104 is a pneumatically operating unit, the details of which need not be described for purposes of the present invention. Briefly, however, the assembly 164 provides a bearing 105 which is cyclically shifted back and forth on a vertical line by the very gradual reciprocable operation of a pneumatic motor 107. The resultant continuous shifting of the axis of drum 6 causes a slight lateral movement of the belt 8 back and forth on the drums 2, 4 and 6. The purpose of such belt shifting is to produce a more uniform sanding of the bowling lane or other floor surface. The pneumatic motor 107 is responsive, in its reversals of movement, to a pneumatically operating nozzle and baffle unit 109 which senses the lateral shifting of the sanding belt 8 between predetermined limits.

At each side of the sanding machine a toggle structure 106 is provided to be used in moving the idler drum 6 backwardly, thereby to release the tension on the sanding belt 8 and aid in its removal from the drums.

At the front of the sanding machine a vertically adjustable roller 108 is provided. This roller is so adjusted as to engage the floor surface and thereby limit the bite of the cut only under unusual conditions.

The pressure drum 4 is rotatably supported by bearings 110 mounted in a rectangular levelling frame comprising side plates 112 and 114 and cross plates 116 and 118. The levelling frame is mounted in the nature of a trunnion having the mutual axis of its pivots extending lengthwise through the machine and intermediate the left and righthand sides thereof. These pivots are indicated at 120 and 122, the fixed portions of the bearings being mounted on the frame cross members 16 and 14, respectively. It will be evident from the description that by virtue of this mounting of the levelling frame the pressure drum 4 supported therein can be maintained in exactly horizontal disposition despite deviations of the main machine frame from the horizontal because of unevenness of the bowling lane or other fioor surface being sanded. This basic mechanical arrangement for the mounting of the pressure drum 4, including the hereafter described cam assembly for effecting the indicated necessary angular adjustments of the levelling frame relative to the main machine frame, is the subject matter of the copending application of Harold W. Martin, Serial No. 207,502, filed July 15, 1962 and entitled Sanding Machine.

Suspended by legs 123 depending from side frame plates 112 and 114 is a platen 125 which has a concave upper configuration conforming to the drum 4 and a flat bottom surface. Between the belt 8 and this bottom surface there is provided a graphiteimpregnated length of canvas 127. Platen 125 is used when making the finer finishing passes across the floor surface, and when the platen is so used the drum 4 does not rotate but merely applies force thereto. When the preliminary rough cutting passes are being made the platen may be removed and the drum 4 will then rotate. When platen 125 is not used the weight transmitted through drum 4 is applied to the floor surface over a much smaller area than when the platen is used, and consequently the cutting pressure will be considerably greater in the former case.

The rearward levelling frame cross plate 118 has at its left a cam track 124 which is inclined downwardly and centrally toward the right (in FIGURE 3) and a cam track 126 which is inclined downwardly and centrally toward the left. A lead screw 123 is freely journalled for rotation in a gear box 1311 mounted on the frame member 12. A traveling nut 134 on lead screw 128 is joined with a carriage 136 having an upper roller 140, which rides flatly against a stationary member 142 forming an extension of the main machine framework, and having a lower roller 138 which straddles the cam track 124. Toward the right-hand side of the machine a second carriage 146 similarly has an upper roller 150 which rides against the member 142 and a lower roller 148 which straddles the cam track 126. Carriage 146 is connected to carriage 136 by a connecting link 144 and thereby a given movement of carriage 136 will result in an identical movement of the carriage 146.

A right angle bevel gearing unit 152 is constantly driven by an extension of the shaft of drum 2 and has a constantly rotating output shaft 154. A pair of normally free-wheeling electromagnetic clutches 156 and 158 are concentric with shaft 154. Within the gear box 130 there is a differential gearing generally indicated 160, through which the lead screw 128 may be rotated in either direction. Upon energization of clutch 158 the shaft 154 will drive the differential through belt drive 162, and upon energization of clutch 156 the shaft 154 will drive differential 160 through belt drive 164. If magnetic clutch 158 is energized the lead screw 128 will rotate in a direction to move carriages 136 and 146 toward the right and if clutch 156 is energized the lead screw 128 will rotate in a direction to move carriages 136 and 146 toward the left in FIG- URE 3. When the carriages 136 and 146 move toward the right, for example, the roller 148 will force the levelling frame plate 118 in a clockwise direction and thereby tend to lower the right-hand side While tending to correspondingly raise the left-hand side of drum 4. If neither of the clutches 156 and 158 is energized, the drum 4 will maintain its position relative to the main machine frame. It will be understood that these angular adjustments of the drum 4 about the axis of pivots 120 and 122 Will be effected as necessary to maintain the axis of the drum in exactly horizontal disposition despite inclination of the main machine frame due to unevenness of the bowling lane or other floor surface. Thereby the floor surface will be sanded evenly, in a truly horizontal plane.

Mounted on the levelling frame side members 112 and 114, and subject to deviations thereof from horizontal position, is a beam 166. Beam 166 has depending legs 168 which are detachably connected to levelling frame extensions 170 by means of latches 172. It should be understood, therefore, that with respect to the horizontal the beam 166 will assume the same angular relation as the axis of pressure drum 4. Afiixed to the beam 166 is a pair of bubble type liquid levels or vials, indicated 174 and 176. These vials are identical, and each comprises a glass container having a slight upward curvature as in the case of any bubble type level. The vials 174 and 176 contain an electrically conductive liquid, preferably methyl alcohol, and electrodes leading from within the vials to an electrical control circuit control the operation of this circuit in response to level or non-level conditions of beam 166. The vial 176 will be referred to herein as the cut right vial because it operates to effect a corrective levelling adjustment when the right side of the bowling lane or other floor surface is sensed as being higher than the left side. The vial 174 will be referred to herein as the cut left vial because it operates in the opposite manner. As illustrated schematically, the vial 176 has embedded therein a tap or electrode 178 which is always immersed in the conductive liquid L and therefore is unaffected by movements of the bubble B. Protruding through the top of the vial 176, however, is a tap or electrode 180 which is insulated from the liquid L by the air gap in bubble B when the vial 176 is in perfectly level position, but which will be immersed in the liquid L if tilting causes the bubble B to move toward the right. In other words, if a voltage is applied across the electrodes 178 and 180 a signal current will not be conducted through the conductive liquid L and the electrodes when the vial 176 is level, but will be conducted when the bubble B shifts to the right by deviation of the vial 176 from the horizontal in a counterclockwise direction. Similarly, the vial 174 has a protruding tap or electrode 172 which is constantly immersed, and an upper tap or electrode 184 which is insulated from the conductive liquid L when the bubble B occupies the central, or level position. In this case, however, if the bubble B moves to the left due to a deviation of the vial 174 from the horizontal in a clockwise direction, a signal current can then be conducted through the electrodes 182 and 184 via the conductive liquid L.

Summarizing what has just been stated, with applied voltages across the respective pairs of electrodes 178, 180 and 182, 184, both pairs of electrodes will be nonconducting when the vials 174 and 176 are held in a level position by their supporting beam 166. If the lefthand side of the beam 166 drop the electrodes 178 and 180 will be conducting and the electrodes 182 and 184 are non-conducting. If the right-hand side of the beam 166 drops the pair of electrodes 182 and 184 will be conducting and the electrodes 178 and 180 will be nonconducting. Upon restoration of the beam 166 to a level position the illustrated condition will be re-established, in which neither pair of electrodes will be conducting.

An electronic control circuit responsive to conditions of the vials 174 and 176 serves to operate the clutches 156 and 158 as is necessary to maintain the beam 166, and consequently the axis of pressure drum 4, exactly horizontal. Each of the vials 174 and 176 has its own,

6 independently operating control circuit. These circuits are identical and, therefore, for brevity of description only the circuit associated with the vial 176 will be described in detail.

Three transformer secondaries, T1, T2 and T3, are supplied from a single primary which is connected to an A.C. supply. T1 supplies 24 volts A.C. across both the vial 176 and a high resistance R1 (680,000 ohm). T2 supplies a lower A.C. voltage (6.3 volts) which is rectified by a rectifier RTl. The voltage from T1 is rectified by a rectifier RTZ but charges a capacitor C2, with the voltage across C2 also appearing across a resistor R3 (1,000 ohm). Transformer secondary T1 is connected in phase with its primary as indicated, and supplies the triggering voltage for a thyratron T in phase with the plate voltage thereof. The control grid circuit for thyratron T comprises the resistor R1, resistor R2, a potentiometer P, and normally closed relay contacts CRlc, and any voltage across these elements appears as a biasing voltage for thyratron T.

When vial 176 is level, thyratron T will be non-conducting due to a negative bias across the resistor R2, which has its negative side connected to the control grid through resistor R1 and its positive side connected to the cathode through potentiometer P, relay contacts CRlc and a cathode resistor R4. This negative bias is sufficient to keep the thyratron from conducting. The bubble B in vial 176 will then be under the electrode 180, and offectively all of the 24 volts A.C. from transformer secondary T1 will be dropped across the vial. If the sanding machine then approaches an area causing the lefthand side to drop relative to the right-hand side, the bubble B will shift (uphill) toward the right and beyond the electrode 180, thereby removing the insulating air gap from below this electrode. The resistance of the vial, i.e. across liquid L and electrodes 178 and 180, will then drop to the point where approximately 12 volts A.C. will override the negative bias at resistor R1. (On the other hand, if the left-hand side rises in relation to the right, the bubble B will remain below electrode and there will be no change of negative bias.) Inasmuch as the overriding A.C. voltage is in phase with the thyratron plate voltage, this tube will conduct on every positive half cycle.

On each pulsation of thyratron T, a relay coil CR1 will be energized and a capacitor C3 in parallel will be charged. This relay has normally open contacts CRla and CRld and normally closed contacts CR1!) and CRlc. As evident from the wiring diagram, energizaton of coil CR1 due to pulsing of thyratron tube T will effect closing of the contacts CRla which are in series with the electromagnetic clutch 158. As previously described, upon energization of this clutch it will be engaged to drive the lead screw 128 in a direction to raise the left-hand end and lower the right-hand end of drum 4.

When relay contacts CRlc open the bypass in the grid circuit for the 24 Volt DC. power supply is removed, and as relay contacts CRld close this power supply is applied across capacitor C4 through a portion of potentiometer P. This voltage is applied in the thyratron grid circuit comprising resistors R1 and R2, and capacitor C4, and accumulates until the grid is sufficiently negative that the A.C. signal from resistor R1 cannot cause the tube T to conduct. This state will effect de-energization of relay coil CR1. The contacts CRla will then open and clutch 158 will disengage. Also, capacitor C4 will now discharge through a portion of potentiometer P and through relay contacts CRld, resulting thereafter in restoration of the DC. negative signal at resistor R1. Assuming that the short duration of operation of clutch 158, in response to the one pulse of thyratron tube T, was not sufficient to bring the cut right vial 176 back to level condition, the bubble B will not have retreated suificiently to insulate electrode 180 from liquid L. Ac-

cordingly, the AC. voltage supplied by transformer secondary T1 will be applied across vial 176 to override the negative bias at resistor R1, and another pulse of thyratron T will again result to re-energize relay coil CR1. This pulsing of the thyratron tube T will continue until successive engagements of the clutch 158 have caused driving movements of lead screw 128 sufficient to return the pressure drum 4 (and also the beam 166 on which the vials 174 and 176 are mounted) back to an exactly horizontal position.

As evident from the foregoing description, according to the invention there is involved a pulse type of operation as distinguished from continuous operation of a mechanism throughout a duration sufiicient to effect proper levelling. Certain advantages of this feature will be treated hereafter. In practice, the pulsations occur in discrete on-off cycles of operation of approximately one second each during operation to effect a levelling correction, although it will be understood that the invention is not limited in scope to this specific timing.

The circuit (as shown at the lower right-hand corner of the wiring diagram) associated with the cut-left vial 174 is identical with that just described in connection with the cut-right vial 176. In the circuit for the cutright vial 176 the counterpart of relay coil CR1 is relay coil CR2, which is energized by the pulsating conduction of a thyratron tube when the vial 174 is caused to conduct an overriding AC. voltage due to dropping of the right-hand side of beam 166 relative to the left-hand side. When this occurs the contacts CR2a are closed by the energization of relay coil CR2 and, the contacts CRlb then being closed as normal, the electromagnetic clutch 156 is engaged. Again, as in the case of energization of electromagnetic clutch 158, the clutch 156 will undergo intermittent engagements in response to the repettive on-or'f pulsations of the thyratron tube which controls relay coil CR2. It is significant to note, for reasons discussed hereafter, that each such pulse results in a very minute levelling adjustment of the pressure drum 4.

Certain interrelated aspects of operation of the relay contacts CRla, CRlb, CRZa and CR2!) may be noted. In series with contacts CR1b and CRZb is a lamp 186, the function of which is to signal that the machine is sanding on the level and that neither of the vials 174 and 176 is sensing a deviation of drum 4 from the horizontal. Accordingly, because of this series connection, when neither of the circuits associated with the respective vials 174 and 176 is operating, both sets of contacts CRlb and CR2b will be in their normally closed positions to cause illumination of lamp 186. This illumination will be interrupted upon operation of either of these circuits to eifect opening of one of the sets of contacts CR1b and CR2b. A lamp 188 is provided to indicate that the left-hand side of the pressure drum 4 has fallen relative to the right-hand side and that in response to the sensing of this condition by the vial 176 the levelling system is in operation to correct the condition. This illumina tion (a flickering in time with the clutch engagements) occurs, of course, because the lamp 188 is connected in parallel with the cut-right clutch 158. A lamp 190 is provided to indicate that the right-hand side of the pressure drum 4 has fallen relative to the left-hand side and that in response to the sensing of this condition by the vial 174 the levelling system is in operation to correct the condition. Lamp 190, being connected in parallel with electromagnetic clutch 156, will flicker in time with its repetitive engagements.

Concluding the above description, the electronic levelling system has proved itself to be highly sensitive and accurate. In addition, the pulse type of operation is highly advantageous in connection with other aspects. It has been found that in a sanding machine wherein accuracy in levelling is very important, as certain devices are brought into play to effect levelling adjustments of a pressure drum or the like relative to a main framework,

variable stresses set up in the machine can raise problems. For example, as the means for effecting a levelling correction begin to operate in response to the level sensing means, the reaction to the involved relative movements produces perhaps infinitesimal but neverthless significant variable stresses. The sensing means sense the absolute position of the cutting parts when in the stressed rather than the normal or unstressed, condition. Therefore, when the sensing means signal that the cutting parts have been restored to an exactly horizontal position, the means for effecting this levelling correction will cease to operate. When this occurs a relaxation of the additional stresses takes place which can produce an overshoot beyond the intended resting place at the exactly horizontal position. However, by virtue of the present pulse system this does not occur because there is no opportunity for any sizeable accumulation of distortion in the frame. Such accumulations tending to produce overshoot do not occur with the use of discrete pulses which operate either of the electromagnetic clutches intermittently.

The levelling system in accordance with the invention has been described in its application to a sanding machine of the type used in the finishing of bowling lanes, where the problem of automatic and accurate levelling is of particular concern. However, within the scope of the invention this system is applicable to other arts in which means responsive to inclination are desired for the production of indicating signals or the operation of external components.

Various other departures from the specifically disclosed embodiment of the invention can be effected without departing from the scope thereof as defined by the following claims.

What is claimed is:

1. In a sanding machine, a travelling main machine frame, an assembly including a travelling abrasive member carried by said frame, means for sensing the position of said assembly in relation to the horizontal, means for shifting the angular relation of said assembly relative to said main frame and the horizontal, and means responsive to said sensing means upon a deviation of said assembly in either direction from the horizontal for operating the last-mentioned means, in the direction to correct said deviation, in discrete, closely spaced and gradual steps continuing until said horizontal position is restored.

2. In a sanding machine, a travelling abrasive member, means operable for corrective adjustments of the cutting angle of said member relative to a horizontal reference, control means for the last-mentioned means including first electrically driven means for effecting corrective adjustments in one direction and second electrically driven means for effecting corrective adjustments in an opposite direction, bubble-type level sensing means containing elecrically conductive liquid and electrodes each being positioned in the path of shifting of a bubble in one of two opposite directions whereby titling produces changes in conductivity of the electrical circuit including conductive liquid and an electrode, independent electrical control circuits, each of said control circuits being coupled between and associated with one of said electrically driven means and one of said electrodes, and being responsive to an aforesaid change in conductivity thereof to supply power to its associated electrically driven means until said reference position is restored, each of said circuits comprising a thyratron, means normally applying to the thyratron a bias voltage to prevent firing of the tube and means responsive to firing of the thyratron tube to transmit driving current to said associated electrical means, the said level coupled to the control circuit being adapted to remove said bias voltage upon a change in conductivity due to deviation of the level from the horizontal reference.

3. The invention according to claim 2, wherein said means operable for corrective adjustments comprise means constantly driven in one direction and reversible means for effecting the actual adjustment in either direction, and wherein said electrically driven means comprise clutches connected between said constantly driven 10 in the path of shifting of the bubble, whereby tilting of each level produces changes in conductivity of the electrical circuit including its electrode and conductive liquid, independent electrical circuits, each of said circuits being means and said reversible means, the engagements of 5 coupled between and associated with one of said elecsaid clutches effecting opposite movements of said reversible means.

4. In a sanding machine, a travelling abrasive member, means operable for corrective adjustments of the cutting angle of said member relative to a horizontal reference, control means for the last-mentioned means including first electrically driven means for effecting corrective adjustments in one direction and second electrically driven means for effecting corrective adjustments in an opposite direction, bubble-type level sensing means containing electrically conductive liquid and electrodes each being positioned in the path of shifting of a bubble in one of two opposite directions, whereby tilting produces changes in conductivity of the electrical circuit including conductive liquid and an electrode, independent electrical control circuits, each of said control circuits being coupled between and associated with one of said electrically driven means and one of said levels, and being responsive to an aforesaid change in conductivity thereof to supply power to its associated electrically driven means until said reference position is restored, each said circuit comprising a power circuit producing closely spaced discrete current pulses to operate its associated electrically driven means in closely spaced gradual steps.

5. In a sanding machine, a travelling abrasive member, means operable for corrective adjustments of the cutting angle of said member relative to a horizontal reference, control means for the last-mentioned means including first electrically driven means for effecting corrective adjustments in one direction and second electrically driven means for effecting corrective adjustments in an opposite direction, a pair of bubble-type levels each containing an electrically conductive liquid and an electrode positioned trically drive means and one of said levels, and being responsive to an aforesaid change in conductivity thereof to supply closely spaced discrete current pulses to its associated electrically driven means to operate the same intermittently in gradual steps until said reference position is restored.

6. The invention according to claim 5, wherein said sanding machine comprises a travelling main frame and a member providing a backing for said abrasive member and determining the angle of cutting thereof relative to said main frame, said member being adjustably mounted in said main frame and subject to the operation of said means for effecting corrective adjustments.

References Cited by the Examiner UNITED STATES PATENTS 977,523 12/10 Gustafson 200152 1,375,278 4/21 Clayton 200-152 X 1,465,500 8/23 Vance 200-152 X 1,676,791 7/28 Mailey 200152 2,338,811 1/44 Hasbrook.

2,446,180 8/48 Haskins 200152.7 X 2,477,927 8/49 Hanson 200-152 2,502,217 3/50 Guibor 200152 X 2,688,217 9/54 Winkler et al. 51-174 3,020,506 2/62 Remington et a1. 200-152 X 3,030,477 4/62 Hensley 200152 LESTER M. SWINGLE, Primary Examiner. FRANK H. BRONAUGH, J. SPENCER OVER- HOLSER, Examiners.

Claims (1)

1. IN A SANDING MACHINE, A TRAVELLING MAIN MACHINE FRAME, AN ASSEMBLY INCLUDING A TRAVELLING ABRASIVE MEMBER CARRIED BY SAID FRAME, MEANS FOR SENSING THE POSITION OF SAID ASSEMBLY IN RELATION TO THE HORIZONTAL, MEANS FOR SHIFTING THE NGULAR RELATION OF SAID ASSEMBLY RELATIVE TO SAID MAIN FRAME AND THE HORIZONTAL, AND MEANS RESPONSIVE TO SAID SENSING MEANS UPON A DEVIATION OF SAID ASSEMBLY IN EITHER DIRECTION FROM THE HORIZONTAL FOR OPERATING THE LAST-MENTIONED MEANS, IN THE DIRECTION TO CORRECT SAID DEVIATION, IN DISCRETE, CLOSELY SPACED AND GRADUAL STEPS CONTINUING UNITL SAID HORIZONTAL POSITION IS RESTORED.

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