Patent GB-1089609-A (GB)
Title: Honing machine with automatic force control
IPC: B23Q15/12
Filed: 1966-08-16
Abstract: 1,089,609. Control of D.C. motors. BARNES DRILL CO. Aug. 16, 1966 [Sept. 17, 1965], No. 36658/66. Heading H2J. [Also in Division B3] A machine for honing the wall of a bore for removing surface roughness therefrom and for enlarging the bore to a, preselected size comprising:- (1) an expandible honmg tool, (2) mechanism for expanding said tool within said bore, (3) an electric motor having a field and an armature driving said expanding mechanism, (4) means for supplying a preselected energizing voltage to said motor, and (5) means responsive to the current drawn by said armature and operable to reduce the terminal, voltage thereof as said current increases with resistance to expansion of said tool, thereby to modulate the current increase and the resulting torque exerted by said motor, is characterized in that the torque of said motor is adjustable independently of said voltage reducing means by a selector which is operable (a) when said armature: voltage attains a preselected low value to increase the torque exerted by said motor and (b) when said armature voltage attains a preselected high value to reduce the torque exerted by said motor, thereby to maintain said voltage within a preselected approximate range. An expansible abrading tool 12 is rotated by an electric motor 17 and hydraulically reciprocated by a piston 23 in a cylinder 22. For expanding the tool, an electric motor 75 drives (through worm gearing 77, 78, worm gearing 81, 82, selectively engagoable clutch 84, shaft 85 and worm gearing 87, 88) a sleeve 89 internally threaded on to a screw 90 on the upper end of a push rod 74 having conical cams (68, 68) co-operating with backing bars (70) carrying the honing stones (67). A motor 91 is connected by gearing 92 to the shaft 85 to shift the honing stones at rapid traverse rates towards and away from the bore wall, the clutch 84 being disengaged. The feed motor 75 is a shunt-wound D.C. motor, e.g. 1/20 H.P., with its armature 92 receiving D.C. current from a rectifier 93 and its motor field winding 101 receiving D.C. current from a rectifier 102; the rectifiers are connected across A.C. lines 94, 95. The D.C. input voltage may be 100 volts. A resistor having a positive temperature coefficient of resistance anda temperature that varies over a wide-range with the rate of current flow through the resistor, e.g. a lamp bulb 104, is connected in series with the motor armature 92 to modulate the progressive increase in current flow through the armature and the resulting torque increase. To vary the honing force throughout the cycle and the maximum force at the end of the cycle produced under control of the lamp 104, the motor torque with a prevailing lamp filament resistance is increased and decreased as the situation requires by a torque selector 105 actuated in response to variations in the armature voltage and operable to increase the motor torque when the voltage drops to a preselected low value (motor 75 at or near stalled condition) and to reduce the torque when the voltage increases to a, preselected high value. The torque selector 105 is a variable transformer controlling the degree of energization of the field winding 101; increase in the field voltage increases the motor torque and decrease in the field voltage decreases the motor torque. The slide 109 of the selector is on the shaft 108 of a reversible motor 107 actuated by a meter relay 110 measuring the voltage across the armature 92, the prevailing voltage being' indicated on a scale 111. To avoid temporary corrections due to transient changes in bore condition a counter 112 is provided to activate the motor 107 only if the condition, remains after a preselected number of strokes of the tool 12. The extent of the corrections is controlled by a timer TD which de-energizes the motor 107 after a timed interval producing the desired increment of selector adjustment. Operation.-At the end of the first downstroke, a switch S4 closes automatically to complete. the D.C. circuit from the rectifier 93 through the feed motor armature 92 to start slow feeding of the stones 67, rapid initial expansion of the tool 12 having been completed by the motor 91. The transformer 105 is initially set. for a low field strength and a motor torque commensurate with the low initial resistance to expansion offered by the inner edges of ridges and high spots in the bore, the torque being sufficient to expand the tool relatively rapidly. Eventually the resistance to expansion rises to a value high enough, as compared to the maximum torque of the motor 75 with the initial field setting, to stall or nearly stall the motor, with a progressive drop in the armature voltage. When the voltage drops to a preselected minimum, e.g. 5-10 volts, the meter relay 110 closes switch S6; at the beginning of the next upstroke, switch S5 closes and a pulse is delivered to the coil 118 of the stepping switch 112 advancing the switch arm 119 to its second contact 121. The switch S6 must remain closed for three successive up strokes before the arm 119 reaches active contact 122 to initiate corrective action. If switch S6 opens during these three strokes, a circuit is made through reset coil 123 to return the switch arm to its first contact 120: When the switch arm 119 reaches active contact 122, timer TD is energized and motor 107 is started in a direction to increase the field voltage and torque of motor 75. After a selected interval, e.g. 2 seconds, timer TD times out, its switch TD1 opening to de-energize the motor 107 and its switch TD2 closing to reset the stepping switch. The torque increase may be insufficient to start the motor 75 if it was stalled. To ensure starting, a resistor 130 connected in parallel with the lamp bulb 104 is brought in at the beginning of the correction making increased voltage available across the armature during the torque correction; this resistance is removed from circuit when the correction has been completed. As a result of a change in the condition of the stones 67 or the bore or as a result of overcorrection, the torque of the motor 75 may exceed the prevailing resistance by an amount sufficient to accelerate the motor significantly, accompanied by a rise in armature voltage. If the voltage rises to a preselected maximum, e.g. 20-25 volts, the meter relay- 110 closes switch S7 and stepping switch 112 is actuated at each upstroke. If switch S7 remains closed during three successive strokes; the motor 107 is energized to run in reverse to reduce the field strength. The increment of reduction is determined by timing out of timer TD or by opening of switch S7 as a result of the reduction in armature voltage, whichever occurs first. A cam 137 on the shaft 108 of the motor 107 co-operates with a switch 134 to prevent reverse rotation of the shaft beyond the desired minimum setting of the transformer 105; a companion cam 138 controls a signal lamp 140. A cam 135 on the shaft 108 co-operates with a switch 129 to prevent forward rotation of the shaft beyond the maximum setting of the transformer 105; a companion cam 140 controls a signal lamp 142. To reset the transformer 105 for minimum field strength at the beginning of each honing cycle, the operator closes manual reset switch 142<SP>1</SP> whereby the motor 107 runs in reverse until cam 137 opens switch 134 at the lower limit of transformer adjustment; a signal lamp 145 is lit during resetting. Two lamp bulbs 104 in series are preferably used. With two bulbs rated at 150 watts at 110 volts the machine produces a maximum of approximately 1000 lbs. of push-rod force. With two 200 watt bulbs a maximum of approximately 2200 lbs. of push-rod force is obtained. In a modification (Fig. 4), feed motor torque is adjusted by a rheostat (147) in parallel with the lamp bulb (104<SP>1</SP>), this control regulating the armature current; reduction in the rheostat resistance increases the motor torque. With a feed motor (75<SP>1</SP>) of 1/150 H.P. the lamp bulb (104<SP>1</SP>) may have a rating of 50 watts at 250 volts and the rheostat be adjustable to 5000 ohms and in series with a fixed resistance (148) of 250 ohms. Automatic adjustment of the rheostat is effected substantially in the same manner as adjustment of the transformer in the previously described embodiment.