US 3627281 A
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Description (OCR text may contain errors)
iinited States Patent 1 3,627,281
[ 72] Inventor Norman L. Peterson Primary Examiner-Robert W. Jenkins Wauwatosa, Wis. Attorney-Marshall & Yeasting  Appl. No. 18,844  Filed Mar. 12, 1970 [45 1 p d Dem 14, 9 ABSTRACT: A control for a transmit-mix truck is arranged to  Assignee Rex Chainbelt, Inc. indicate for each revolution of the mixer drum, whether the Mflwaukee,wis drum speed is below a predetermined minimum or above a predetermined maximum speed, to count those resolutions occuring at speeds between the predetermined speeds, and to in-  MIXING TIMER itiate a change from mixing to a slower agitating speed when a 5 (Ilaims, 3 Drawing Figs. predetermined number of counted revolutions are recorded.
In a preferred structure a pair of slow drop out timing relays mag and a control relay are briefly energized at least Once each  w 255/175 revolution of the mixer drum. Contacts on the relays are arranged such that a first capacitor is charged immediately fol- 235/1502 259/8 lowing the brief energization of the relays and is discharged  References Cited through an indicating light if the next relay energization occurs before the expiration of a first-timing interval. The relay UNITED STATES PATENTS contacts are also arranged such that a second capacitor is l,7l4,475 5/1929 .laeger 259/163 charged at h expiration f h fi mi i int rval and is 1,764,533 6/1930 259/163 discharged through a counter in the event the relays are enerl 1953 Osborne 259/175 gized prior to the expiration of a second-timing interval or is 9 3/1960 Swartholll N 259/175 X discharged through a second-indicating light in the event that second-timing interval expires before the next energization.
+ HY Moron FAST TIMER I, I I: SLOW TIMER l7- L CRl ll 11/ 20 CR2 l CR2 VOLTAGE COMPARATOR H H HYofPuMP n u CR4 CR 3 mmsnmmwn 3.627281 SHEET 1 OF 2 HYD. MOTOR IO ,3 *5 8- FAST TIMER I 9 L SLOW TIMER 4 .2 I3/ GKFTR I5 HHflDJUSTABLE COUNTER I-- (STR l l4 l6 TOTAL TIMER l8 El 17'- L IL. 1v 20 VOLTAGE COMPARATOR IL HYD. PUMP u 1 W T CR4 CR3 MIxrNo TIMER BACKGROUND OF THE INVENTION In some processing operations the speed of operation as well as the total time is important. One such operation is mixing concrete in transit-mix trucks. Unless the batch of material is adequately mixed for a predetermined time the resulting concrete lacks strength. For quality control, it is therefore necessary that the mixer drum be operated above a certain minimum speed and below a certain maximum speed for a given number of revolutions. After the mixing is completed, the speed of the drum should be reduced to slowly agitate the mix until it can be delivered.
SUMMARY OF THE INVENTION A relay circuit incorporating a control relay and a fast and a slow time delay relay cooperates with a momentary contact switch operated by the truck mixer drum to actuate a fast indicator lamp or a slow indicator lamp if the drum speed is out of tolerance or a counter if the drum speed is within tolerance. The time delay relays are reset, to start new timing intervals, at each operation of the drum-operated switch, regardless of whether or not the relays have timed out from the previous reset. During reset of the timing relays contacts of the control relay sample the condition of the timing relays. Condensers, charged during the timing intervals, are discharged through one or the other of indicator lights according to whether the sampling occurs during the first-timing interval (fast-timing relay) or after the expiration of the second-timing interval (slow timing relay). If the sampling occurs after the expiration of the first-timing interval and before the expiration of the second-timing interval, one condenser is discharged through the counter device coil to register a count.
The counter is preferably of a preset type adapted to close an external circuit when the preset count is accumulated. This external circuit may include an indicator to advise the truckdriver that his load is mixed, or it may be connected into a servomechanism arranged to control the displacement of a variable displacement hydraulic pump that is connected to a hydraulic motor connected to and driving the mixer drum. In this arrangement the servomechanism first sets the pump displacement to drive the drum at mixing speed. Then when the counter is filled, the servomechanism reduces the pump displacement to slow the mixer drum to agitating speed.
As a quality control feature, it is also desirable to include a second counter, connected to respond to every revolution of the mixer drum during mixing and agitating to show excessive mixing or agitation that might adversely affect the quality of the concrete.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a transit-mix mixer drum control, including timers, counters, and drum speed control means.
FIG. 2 is a circuit diagram of one circuit, including timers, storage condensers, indicator lights and counters.
FIG. 3 is a circuit diagram of another circuit, generally similar to FIG. 2, but employing different components in a slightly different arrangement.
DESCRIPTION OF THE PREFERRED EMBODIMENT The general operation of the circuits according to the invention are illustrated in FIG. 1. As indicated in this figure, a wiring diagram current may flow from a positive supply lead 1 through a single-pole double-throw cam-operated switch 2 to a fast and a slow timer 3 and 4 connected to a return lead 5 as long as the switch 2 is in its normal position with its movable contact 6 in contact with its fixed contact 7. The switch 2 is a form of limit switch that is actuated once for each revolution of the mixer drum 8 as a lug 9 on the drum passes the operator ofthe switch 2.
The mixer drum is preferably driven by a hydraulic motor 10 which, in turn, is driven by a hydraulic pump Ill. The pump III, by means not shown, is driven from a separate engine or from the mixer truck motor through a power takeoff. The hydraulic pump 11 is of the variable positive displacement type in which the displacement may be varied by a control motor 12.
When the mixer drum lug 9 actuates the switch 2 to drive its movable contact against its fixed contact 113 current may flow through the contact 13 to a total revolution counter 1141. When the limit switch 2 is thus operated current may also flow through an adjustable counter 15 provided normally open contacts FTR of the fast timer 3 have closed, indicating that the fast timer has completed its timing interval, and provided that slow timer contacts STR are still closed, indicating that the slow timer 4 has not completed its timing interval. The adjusting counter 15 is arranged to close a circuit when the count reaches a prescribed number to energize the coil of a control relay that is connected between contacts of the adjustable counter 15 and the return lead 5. The control relay is preferably a type that responds to a pulse of current and then remains in its circuit closing position until it is manually reset.
The control relay has normally open contacts CR1 and normally closed contacts CR2 arranged to select a control voltage from either a low-speed adjust potentiometer 116, in the event that the normally open contacts CRll are closed, or a highspeed adjust potentiometer 117 in the event the normally closed contacts CR1 are closed. The low-speed potentiometer 16 is energized from the supply lead 1 through a resistor I8 and has its other terminal connected to return lead 5. Thus the voltage on a slider 19 of the potentiometer 16 may vary from the voltage on the lead 5 to some voltage intermediate the voltages on the lines II and 5. The high-speed potentiometer 17 is connected between line I and a resistor 20 connected to the return lead 5. Thus the voltage or potential on the slider 2l may be varied from the potential of the supply line l to some potential intermediate that of the lines I and 5.
The lead 22 connected to the common pole of the normally open and normally closed contacts CR1 is connected through normally closed contacts CR2 to a lead 23 connected as one input to a voltage comparator 24.
A second input to the voltage comparator 2d is supplied through a lead 25 from a slider 26 to a follower potentiometer 27. The potentiometer 27 is electrically connected to the leads 1 and 5 and has its slider mechanically connected to the output shaft of the electric motor 12 that is connected to vary the displacement of the hydraulic pump 111. Thus connected, the position of the slider 26 varies according to the position of the displacement varying member of the hydraulic pump Ill and serves as a position follower for the servomechanism. The voltage comparator 24 is arranged to selectively energize a pair of control relays CR3 and CR4 according to the sign of the difference between the voltages applied to its inputs on the leads 23 and 25. The control relays CR3 and CR I have normally open contacts arranged to reversibly connect the electric motor 12 to the power leads l and 5.
To provide for remote adjustment, a fourth potentiometer 32 is connected between the leads l and 5 and has its slider 31 connected through normally open CR2 relay contacts to the lead 23 leading into the voltage comparator 24. The NO. contacts CR2 are controlled by a coil CR2 which in turn is energized through a remote manual pushlbutton 32 and lead 33 connecting the coil to the supply lead l. The other side of the coil is returned to the return lead 5.
The equipment illustrated in FIG. 1,. in operation, provides for operating the mixer drum 8 at selected adjustable speeds that include a first or high-speed operation for mixing when the voltage comparator receives its signal from the slider 21 and adjusts the displacement of the hydraulic pump 11 correspondingly. Then, as soon as a sufficient number of revolutions of the mixer drum 8 have been completed at speed within the speed tolerance, the adjustable counter 15 reaches its preset count and it, through the latching control relay CR1,
switches the control to the low-speed adjust potentiometer 19 so that the servomechanism including the voltage comparator then rests the hydraulic pump to a lower displacement to reduce the speed of the mixer drum. This speed is maintained to agitate the material unit it is discharged at the point of use.
When ready to discharge the material, the operator may close a remote switch 30 to energize the coil of CR2, the contacts of which connect the comparator lead 23 to a slider 31 of a fourth potentiometer 32 which may be set to give the proper speed for discharging the batch of material from the mixer drum 8.
While not shown in detail, the adjustable counter may be any of the commercially available contact making counters or it may be plurality of stepping switches arranged in decade fashion such that a first or units decade responds directly to operations of the limit switch 2 and such that higher order decades respond to circuit completions of the lower order decades. If a stepping switch arrangement is used it may be wired to cooperate with a set of selector switches to complete the circuit to the control relay CR1 after a selected number of steps have been recorded. If the stepping relays are used they may be reset by supplying, to the drive coil of each decade, current pulses from a low-frequency oscillator until the relay wiper reaches a particular contact.
A relay circuit including timing relays operated from the switch 2 to determine whether or not the adjustable counter should count the particular revolution of the drum 8 is illustrated in FIG. 2. As shown the switch 2 has its movable contact 6 connected to the supply lead 1, and has its first fixed contact 7 connected through a lead 35 to the fast timer relay 3 and a slow timer relay 4. These relays may be of the motor operated variety or the solenoid type with dash pot timing control arranged so that their timing intervals start as soon as the contacts 6-7 are closed and so that they reset whenever the contacts 6-7 open. The normally open contact 13 of the switch 2 is connected through a lead 36 to a control relay coil 37 and to a counter 14 which records the total number of revolutions of the mixing drum 8 regardless of its speed.
The circuit for sampling the condition of the timing relays 3 and 4 at the end of each revolution of the mixing drum 8 is energized through a resistor 40 that is arranged, through normally closed contacts 41 of the control relay 37 and normally closed contacts 42 of the fast-timing relay 3, to charge a condenser 43. The condenser 43 is discharged through normally open contacts 44 of the control relay 37 in the event the revolution of the drum is completed to reenergize the control relay 37 before the fast-timing relay 3 has timed out. In this case the discharge of the condenser is through an indicator light 45, the flashing of which indicates that the mixing drum is turning too rapidly. If the fast-timing relay times out before the completion of the revolution of the drum that relay opens its contacts 42 and closes its normally open contacts 46 to discharge the condenser 43 through a resistor 47. At the same time, the fast-timing relay 3 closes into contacts 50 to supply a circuit through normally closed control relay contacts 51 and normally open slow timer relay contacts 52 to charge a second condenser 53. The condenser 53 is discharged through the slow timer relay contact 52 and normally open control relay contact 55 and a coil of the adjustable counter in the event the revolution of the mixer drum 8 is completed prior to the timing out of the slow timer 4. In the event the slow timer times out prior to the completion of the revolution of the drum, and operation of the control relay 37, the slow timer 4 closes its contacts 56 to discharge the condenser 53 through an indicator its thus indicating that the drum is turning too slowly.
It may be noted in this circuit that the condensers are charged during the initial portion of the timing intervals and are discharged either through indicating lights, a resistor or the adjustable counter depending upon the condition of the timing relays when the revolution of the drum is completed.
A modified circuit for accomplishing substantially the same results is shown in FIG. 3. In this arrangement power from a lead la is conducted through contacts 6a-7a of a switch 2a, and lead 60 to a total-indicating counter 61 that is connected to a return lead 5a. A coil of a control relay 62 is connected in parallel with the counter 61. Furthermore, through a resistor 62 and a diode 63 current flows to energize a fast time relay 64 the timing period of which is controlled by a parallel condenser 65. At the same time current also flows through a second diode 66 to energize a slow time relay 67 the timing period of which is controlled by a condenser 68.
A sampling circuit to test the condition of the timing relays at the completion of a revolution of the mixer drum is taken through a resistor 70, nonnally closed contacts 71 of the control relay 62 and a first branch including normally open contacts 72 of the fast-timing relay 64 to charge a condenser 73. Thus the condenser 73 is charged as soon as the control relay 62 drops out after the momentary closure of the switch 2a. Should the drum revolution be-completed before the expiration of the timing interval of the fast timer 64 the condenser 73 is discharged through the contacts 72 and normally open contacts 74, of the control relay 64, leading to an indicator light 75. In the event the fast time relay 64 times out before the completion of the revolution of the mixer drum the relay closes into contacts 76 to discharge the condenser 73 through a resistor 77.
Also when the fast timer times out it closes its contacts 78 to complete a circuit through a diode 79 to a second condenser 80. In the event the revolution of the drum is completed and the control relay 62 is operated before the slow timer relay 67 releases, a circuit is completed to discharge the condenser 80 through slow timer relay contacts 81 and control relay contacts 82, connected in series, to an adjustable counter 83 to register a count indicating a revolution of the mixing drum at an acceptable speed. in the event the slow timer 67 releases or times out prior to the completion of a revolution of the drum, it closes its contact 84 to complete a circuit through an indicator light 85. This circuit is supplied through the resistor 70, the control relay contact 71, the fast timer relay normally closed contacts 78 and the diode 79 to hold the indicator light on until the completion of the drum revolution when the contacts 71 are opened. As soon as the contacts 71 open the condenser 80 is discharged through the indicator light 65 in preparation for the next cycle.
This circuit thus performs all of the functions of the circuit illustrated in FIG. 2.
Either of these circuits, when used in the system illustrated in FIG. 1, provide means whereby an inspector or operator may know whether or not certain prescribed mixing procedures have been carried out with each batch of concrete mix.
1 claim 1. Apparatus for monitoring the operation of a mixing drum comprising, in combination, switch means operated by the mixing drum, relay means connected to and operated by said switch means, a first and a second timer operatively connected to said switch means for timing a first and a second interval following each operation of said switch means, a first and a second capacitor, contacts on said relay means and said first timer connected to complete a charging circuit to said first capacitor during that portion of a cycle of said switch means that occurs during said first interval, contacts on said relay means and said timers connected to complete a charging circuit to said second capacitor during the remaining portion of the cycle of the switch means and second time interval that occurs after said first interval, contacts on the first and second timers connected to discharge the first and second capacitors at the close of the respective timing intervals. contacts on said relay means connected to discharge said capacitors upon operation of said switch means and a counter connected in the relay completed discharge circuit of said second capacitor.
2. Apparatus according to claim 1 in which indicating means is included in the discharge circuits completed by the contacts of the second timer.
operatively connected to said counter, and speed regulating means for said mixer operatively connected to said control means for varying the speed of rotation of the mixer in response to a predetermined count accumulated in said counter.