US 3254289 A
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R. E. HARTMAN OPERATING MECHANISM FOR PARTITIONING MEANS AND THE LIKE AND MOTOR CONTROL SYSTEM Filed May 28, 1962 May 31, 1966 M T Te INVENTOR. Roy Hartman BY Gad/s Moo/m 44M A TTORNEYS United States Patent 3,254,289 OPERATING MECHANISM FOR PARTITIONING MEANS AND THE LIKE AND MOTOR CtUN- TROL SYSTEM Ray E. Hartman, RED. 2, Box 189-A, Tiiiin, Ohio Filed May 28, 1962, Ser. No. 198,061 6 Claims. (Cl. 318-476) This invention relates to the control of electric motors and particularly to an electric motor driven system for raising and lowering stage equipment, gymnasium equipment, and partitioning means and to safety control sys tems for the same. An object of this invention is to provide a control system for the driving motors for mechanisms of the'type which elevate and lower partitions on stages and in gymnasiums and the like. Another object is to provide for the accurate control of the operation of electric motors where there are variations in the loading in accordance with a predetermined pattern. A further object is to provide for the control of such motors where it is desirable to protect against the imposition of an unpredicted load. A further object is to provide such control as to give absolute assurance against continued operation when an excessive load is imposed upon the motor. Another object is to provide for the control of electric motors which operate staging equipment and the like. These and other objects will be in part obvious and in part pointed out below. In the drawings, the single figure is a schematic representation of one embodiment of the invention.
The illustrative embodiment of the invention is in the form of an elevatable partition curtain in a school gymnasium. The curtain comprises fabric such as heavy duck or nylon arranged to form a plurality of accordionpleated sections each extending the horizontal dimension of the partition (e.g., 100 feet). When the curtain partition is in place, the fabric sections form a continuous wall (e.g., 21.feet high). The top of the curtain is connected to an overhead support, and the bottom carries a weighted member which rests upon the floor. When it is desired to remove the partition, the bottom member is lifted by a plurality of cables extending from the overhead support. As this bottom member moves upwardly, the successive sections of the curtain fold or hinge in an accordion-like fashion to a substantially horizontal position so that the partition is collapsed into a stack of horizontally positioned sections which is supported from above.
During the lifting or elevating operation, the initial load on the cables is very small because only the bottom one or two of the sections is being lifted. However, the load on the cables increases progressively as the sections move to their collapsed or horizontal positions. The cables are drawn upwardly by winches which are driven by an electric. motor. Hence, the load on the electric motor varies over a relatively wide range because of the variation in the load which is being lifted. This variation in the load is greater than those normally encountered with elevating systems of this general type. However, with installations in schools and the like, great care must be taken to avoid possible injury to people who may be in the vicinity of the partition at the time it is lifted. For example, a persons clothes might become entangled with the mechanism and in such event, it is necessary to stop the electric motors immediately. The present invention provides control whereby the motor is operated to perform the lifting operation under the widely varying load conditions, and yet the motors are stopped whenever an abnormal load appears. Hence, if anything other than the partition sectionsis lifted, or if the sections do not fold together properly, the motor is stopped,
3,254,289 Patented May 31, 1966 Referring to the drawing, in the lower right-hand corner is shown a three-phase induction motor 2 the output shaft of which is connected by conventional means (not shown) to the load, that is, mechanism for raising and lowering a partition in a gymnasium. Motor 2.is supplied with power through three lines 4, 6 and 8, lines 6 and 8 of which are connected directly to conventional controls in a control box 10 including the usual starting and reversing controls, a key switch 18, and UP push button and a DOWN push button 22. 'The control box 10 also typically includes a fused main switch for making a connection to the main supply lines 12, 14 and 16.
Motor line 4 is connected to the control box 10' through a small resistor 24 and a line 26. When the motor is operated, resistor 24 develops a voltage corresponding in amplitude and phase to the current flowing through motor line 4, and this voltage is transmitted through wires 36 and 38 to the primary 40 of a transformer 42 which furnishes signals to a power detection circuit to be described hereinbelow. This power detection circuit also is furnished a reference voltage from the secondary 66 of a transformer 46. The upper end of the primary 44 of transformer 46 is connected to supply line 26, and the lower end of the primary is connected to the center tap 50 of a primary winding 32 which is connected by wires 28 and 30 to supply lines 8 and 6, respectively. With this arrangement, the reference voltage developed across secondary winding 66 is in phase with the power component (i.e., the non-reactive component) of the voltage across the upper half of secondary 52, and will be out of phase with the power component of the voltage across the lower half of the secondary 52.
The reference voltage across secondary winding 66 is connected by wires 64 and 68 to a voltage-dividing circuit consisting of series-connected resistors 70 and 72. The upper end of the resistor 70 is connected to the center tap of secondary winding 52 of transformer 42, and the lower end of this resistor 70 is connected through a pair of rectifier circuits 58 and 60 to the remote ends of the secondary winding 52. The net voltage applied to the first rectifier circuit 58 is the vectorial combination of the voltage across resistor 70 and the volt-age across the-upper half of secondary 52, while the net voltage across the other rectifier circuit 60 is the vectorial combination of the voltage across resistor 70 and the voltage across the lower half of the secondary 52. Any in-phase current component through resistor 24 (i.e., a current component representing rea power furnished to the motor 2) will produce in the upper' half of secondary winding 52 a voltage which adds to the reference voltage across resistor 70, and correspondingly will produce in the lower half of the secondary 52 a voltage which subtracts from the reference voltage across resistor 70. Therefore, any increase in the in-phase current flowing through resistor 24 will cause an increase in the direct current voltage developed across capacitor 57 of rectifier circuit 58, and a corresponding decrease in the direct current voltage developed across capacitor 59 in rectifier circuit 60. Thus there will be a net increase in the difference in potential between the two terminals 61 and 65, which represent output terminals of the power detection circuit. Moreover, this change in potential difference is linear with respect to the change in real power.
If there is a change in the reactive power or out-of-phase current flowing to motor 2, the change in current through resistor 24 develops at transformer 42 a voltage component which is out of phase with respect to the reference voltage across resistor 70*. Because the output of transformer 42 is added vectorially to the reference voltage, this reactive power component will produce the same effect on rectifier circuit 58 as it does on rectifier circuit 60. Accordingly, there will be no net change in the potential at output terminals 61 and 65.
Output terminal 65'is connected to a bias-setting circuit which determines the potential of terminal 65 with respect to ground. To this end, terminal 65 is connected through a line 80 and a first isolating resistor 82 to the movable arm of a potentiometer 88, and also from line 80 through a second isolating resistor 84 to the movable arm 94 of a potentiometer 92. Potentiometer 88 is connected between a positive voltage bus 90' and ground, while potentiometer 92 is connected between the positive voltage bus 90 and a negative voltage bus 96. Positive bus 90 is provided with a filter capacitor 91, and receives power through a diode 138 and a resistor 136 which is connected through a line 132 to a secondary winding 134 on transformer 34. Negative bus 96 is provided with a filter capacitor-=140, and receives its power from a diode 128 and a resistor 130 which is connected to the line 132.
Potentiometer 88 provides an adjustment for setting the cut-off power level, i.e., the overload point at which the control circuit shuts down the supply current to the motor 2. Potentiometer 92 provides an automatic adjustment of the cut-oif power level with changes in position of the device being driven by the motor, to take account of the normal or predetermined pattern of changes in load that take place during operation of the equipment. For this purpose, the movable arm of potentiometer 92 is shown connected to a gear reduction means 3 which in turn is connected to the output shaft of motor 2.
In the normal operation, the biasing circuit formed by the potentiometers 88 and 92 causes the connecting line 80 and output terminal 65 to be positive with respect to ground. If there is no current flowing through the line resistor 24, the direct current voltage across capacitors 57 and 59 are equal, and therefore the potential on the other output terminal 61 also is positive with respect to ground. Output terminal 61 is connected through a line 114, an RC filter 110 and 112, and a resistor .108 to the base of a transistor 100, the emitter of which is grounded. The collector of this transistor 100' is connected through a line 99 to a relay winding 98 the remote end of which is connected to the negative bus 96.
Normally, the potential on the output terminal 61 is such as to prevent sufficient current flow through the collector of the transistor 100 to operate relay 98. If the load on the motor 2 goes up, the resulting increase in the in-phase current passing through the line resistor 24 causes a corresponding increase in the difference in potential between output terminals 65 and 6:1 and this decreases the potential of terminal 61 with respect to ground. If the load goes beyond a predetermined safe level, the potential on terminal 61 will drop to zero and then increase negatively to produce electron current flow through line 114, resistors 112 and 108 and into the base of transistor 100. This base current, combined with an auxiliary base current supplied through resistor 106 from a source to be described, is sufficient to cause a collector current large enough to operate the relay 98. As will be explained, actuation of this relay shuts off the current to the motor 2.
The transistor base current supplied through resistors 112 and 108 is limited by two factors, the first of which is that the potential difference between output terminals 65 and 61 cannot increase beyond the value reached when the voltage across resistor 70 equals the voltage on the lower half of the secondary 52. In addition, this base current is limited by a diode 148 which is connected by line 150 to the juncture between resistors 108 and .112, this limiting diode being supplied by a voltage-divider circuit 142 and 146 which is connected between the negative bus 96 and ground. The parameters of the various control circuit elements are so set that the current that can be supplied to the base of transistor 100 through resistors 112 and 108 is only approximately 60% to give a collector current sufficient to pull in relay 98.
The transistor .100 also receives base current from a circuit which includes a resistor 106, line 118, resistor 124 and negative bus 96. A Zener diode 120 is connected between line 118 and ground in order to regulate closely the value of the voltage at this point. The normal voltage of supply line 118 is set to supply only approximately 60% of the base current needed to give a collector current large enough to pull in relay 98.
When the motor 2 is first turned on, as by pressing the UP or DOWN push buttons or 22, power is applied immediately through transformer 34 to the positive and negative buses 90 and 96. However, the build-up of voltage on the transistor supply line 118 is delayed by a capacitor 126 which is connected to the resistor 124. The time-constant of this RC circuit is set sufficiently long to delay the build-up of normal voltage on line 118 until after the transient overload of the supply current during start-up of the motor 2 has subsided. This delay typically will be only about one'or two seconds. When the motor power is turned oif, as by releasing the UP or DOWN push button or in response to operation of relay 98, capacitor 140 discharges rapidly through resistors 142 and 146 which are of low ohmic resistance, and capacitor 126 discharges rapidly through a diode 122 connected in parallel with resistor 124. Thus the system quickly is made ready for the next operation.
To summarize, in the transistor supply circuitry there are two sources of current for the transistor base either of which has by itself insufficient capacity to produce enough electric current to pull in and operate the relay 98, but which together are more than of sufficient capacity for operating the relay. During the start-up of motor 2, the energization of one of these supply circuits (i.e., supply line 118) is delayed for a short period of time to assure that there will be no actuation of the relay 98 as a result of the transient overload current to the motor. Thereafter, the relay 98 will be actuated whenever the motor 2 is'overloaded beyond a predetermined level.
When the contacts 97 of relay 98 are closed, this completes an energizing circuit between lines 152 and 154 to the'winding 156 of a second relay 164. This energizing circuit includes line 158 which receives alternating current power from the control box 10, the return circuit being through line 159. When the relay 164 is pulled in, its upper contacts'open to break a circuit between line 159 and line 162, and thereby (by conventional means not shown herein) cut off the power fed to the motor 2. The lower contacts of the relay 164 close to parallel the closed cont-acts 97 of relay 98, and thereby hold the relay 164 actuated until released by the usual reset circuit.
The motor control system disclosed hereinabove is effectively responsive only to real power overloads, since changes in out-of-phase current do not influence the difference in potential between output terminals 61 and 65. For example, if the line voltage fluctuates without any change in real load on the motor, the resulting change in current through resistor 24 will cause essentially no change in the potential difference between terminals 61 and 65. On the other hand, if a 60 pound child attempted to ride up on a 500 pound gymnasium partition, the change in real load on the motor would immediately be detected, and the motor would be stopped. It should particularly be noted that a power detector responsive only to the amplitude of current through resistor 24 would not provide the high sensitivity of the present apparatus, because a change in real load causes only a relatively small change in current amplitude, but a large change in the inphase current. Since the present apparatus is phase-responsive, its sensitivity to changes in real load is very great.
As many possible embodiments may be made of the electrical and mechanical features of the above invention and as the art herein described might be varied in to of the amount needed various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings is to be interpreted as illustrative and not in a limting sense.
1. A system for elevating a sectional partition wherein the sections are lifted serially so that the load is increased as additional sections are lifted, the combination of, an electric motor which is operated to perform the elevating operation and a safety control system for said motor comprising means responsive to the in-phase motor current, means to stop said motor upon a rise in the in-phase motor current above a permissible limit, and means synchronized with the movement of said partition to change said permissible limit in accordance with the general pattern of the change in the actual load during normal operation.
2. A system as described in claim 1 wherein said motor is an induction motor and wherein said means responsive to the in-phase motor current includes a circuit element in one of the lines supplying current to said motor, and means to produce a control voltage which varies with the in-phase current flowing through said circuit element.
3. In a motor control system, the combination of, means connected to one of the lines supplying electric current to the motor to produce a voltage corresponding to the energization of said motor, means responsive to said voltage to produce a direct current control potentialwhich varies directly with the magnitude of the in-phase current to said motor, means to produce a variable potential which is varied in accordance with a predetermined pattern dependent upon the anticipated change in load during an operation cycle of the motor, and relay means responsive to an increase in said control potential beyond a permissible limit as modified by said variable potential.
4. A system for elevating a partition wherein the portions thereof are lifted serially so that during each operating cycle the load is increased as additional portions are lifted, the combination of, an electric motor which is energized to effect the elevating movement, cut-ofi means responsive to changes in the load on said motor and including means to stop said motor whenever the load thereon exceeds a set level, said cut-off means being adjustable to permit alteration of said set level, and a safety system for said motor comprising control means operating in synchronism with the movement of said partition when the latter is moved by said motor, said control means being coupled to said cut-01f means and acting throughout each operating cycle to change said set .level in accordance with a predetermined schedule corresponding to the pattern of the changes in the actual load during said operating cycle.
5. Apparatus for moving equipment through a range in Which the load normally varies in accordance with a fixed pattern, comprising, in combination, an electric motor the output of which is to be connected to said equipment to effect the required movement thereof, overload cut-out means responsive to changes in the load placed on said motor and operable to stop said motor whenever said load exceeds a set level defining a permissible limit, adjustment means for altering said set level, and control means coupled to the output of said motor to be driven in synchronism with the movement of said equipment, said control means operating to vary said adjustment means to change said set level according to a predetermined schedule corresponding to the normal changes in load on said motor occurring during a normal operating cycle of said equipment.
6. Apparatus as claimed in claim 5, wherein said control means actuates potentiometer means to produce a control signal which varies according to said predetermined schedule, said cut-out means including means responsive to said control signal to effect the required change in said set level.
References Cited by the Examiner UNITED STATES PATENTS ORIS L. RADER, Primary Examiner. J. C. BERENZWEIG, R. COOKE, Assistant Examiners.