Consistency Control For Slush Freezer

Abstract

Liquid feeds from the upper reservoir to the lower refrigerated chamber where it is frozen on the walls. The scrapers and blades in the lower chamber scrape ice from the walls and keep the liquid/ice mix agitated. The slush is drawn off to be served. As the ice content increases, the load on the scraper drive increases. When the desired consistency is reached, the control shuts down the refrigeration. The control responds to torque and requires a sustained torque for a predetermined period to respond and shut down the compressor. The compressor is not restarted until the torque has dropped to a predetermined lower value.

Description

BACKGROUND OF INVENTION

The most effective control for slush machines has heretofore employed a drive motor which was rotatably mounted so the motor casing rotated in response to increasing torque. The motor was biased in one direction and rotation of the casing was resisted by a shock absorber. Therefore, momentary increases in torque had no effect. The greater the damping by the shock absorber, the greater the time delay but the delay worked in both the torque increasing and decreasing directions. And, from a practical matter, the time delay available left something to be desired. Further, as the torque gradually increased with interspersed shock loads, the motor would work towards the shut-down position so that only a very short time at maximum torque was required to initiate shutdown.

SUMMARY OF INVENTION

The present device does not start measuring the delay period until the desired torque is reached and at that time the time delay starts. Any decrease in torque below the set level will cancel the accumulated time and require starting the period over again. Therefore, there must be a sustained torque for a given period. After the prescribed time delay, the refrigerant compressor shuts down and can be restarted only after the torque has fallen to a prescribed low value. With the positive control over the time delay, the quality of the slush product is improved.

DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical section through a slush machine to give the environment of the control.

FIG. 2 is a perspective view of the motor and control switches.

FIG. 3 is a simplified schematic wiring diagram showing the principles of the control.

DESCRIPTION OF PREFERRED EMBODIMENT

The slush machine shown in the drawings includes a cylinder 10 having an upper reservoir 12 and a lower freezing chamber 14. The chambers are separated by a divider plate 16 which does not have a tight fit to, therefore, allow liquid to flow from the upper chamber to the freezer chamber to maintain the freezing chamber full. The refrigerated or freezer chamber is surrounded by coils 18 which constitute the evaporator of a refrigeration system. The chamber is provided with a central post 20 which extends up through the chamber and, in effect, provides a standpipe preventing liquid flowing out of the freezer chamber. The drive shaft 22 extends from the lower end where it is guided in bushing 24 to the upper end where it is connected to the agitator shaft 26 which extends back down into the refrigerated chamber with its lower end guided on bushing 28. The agitator shaft carries the scraper blades 30 and the mixing blades 32 which function to scrape the ice from the cold wall and move the ice particles upwardly in the refrigerated chamber. The product is dispensed through the valve assembly 34. For draining purposes a lower valve 36 is provided.

At the bottom of the machine there is an electric motor 38 which drives shaft 22 through reduction gearing in housing 40. The housing is supported on bearing 42 so that the motor and reduction gearing is rotatable relative to the slush machine. FIG. 2 shows the manner in which the motor and gear assembly is biased clockwise by spring 44 which is compressed between the bushing 45, anchored to the machine frame by lug 47, and the end of rod 49 connected to arm 46 extending from the mounting plate 48. The mounting plate is provided with two switch actuating arms 50,52. The bias, therefore, acts to urge the motor in a direction whereby the arm 50 will contact the plunger of switch S.sub.1. The motor stub 54 connects into the bottom of the shaft 22. Shaft 22 turns the scraper and blades and increasing consistency of the slush in the refrigerated chamber will act to increase the torque load on the motor whereby the motor will tend to rotate as the load increases. This will move the actuating arm 50 away from switch S.sub.1 and eventually bring actuating arm 52 into contact with switch S.sub.2 when a predetermined load is reached as determined by the spring characteristics. This is utilized to derive the control function to obtain and maintain the desired consistency in the slush. FIG. 3 shows a simplified schematic of the control system.

As may be seen in the schematic, when the on-off switch is closed, the motor is energized and the mixing blades and scraper are placed into operation. These will continue in operation so long as the slush machine is in use. Due to the action of the bias spring on the motor mount, the normally open switch S.sub.1 will be closed. This will cause relay No. 1 to be energized through the normally closed time delay switch S.sub.3 which is operated by relay No. 2. Energization of relay No. 1 will close normally open switches S.sub.4 and S.sub.5. Closure of switch S.sub.5 puts the refrigeration compressor 56 across the line L.sub.1 ,L.sub.2 and starts the freezing operation. Closure of switch S.sub.4 puts a shunt around switch S.sub.1 so that the compressor 56 will continue in operation after switch S.sub.1 opens by reason of the torque load increasing slightly and the actuating arm 50 moving away from switch S.sub.1.

With switch S.sub.4 closed there is a voltage supply to the resistor R and the silicone controlled rectifier SCR which is initially in its non-conducting state. The voltage supplied through the dropping resistor R tends to build a charge on the capacitor C but since switch S.sub.2 is closed the charge cannot build up, the charge being leaked off to ground.

After the torque increases sufficiently for the motor to rotate against the spring load to open the normally closed switch S.sub.2, the charge can start building up on the capacitor and will do so at a rate determined by the RC time factor of the components. Desirably in about 75 seconds the charge on the capacitor and, hence, at junction 58 will build up to the breakdown voltage of neon bulb NE whereupon the neon will trigger the SCR to the conductive state. This, in turn, will energize relay No. 2 which will open switch S.sub.3. This will de-energize relay No. 1 and open switches S.sub.4 and S.sub.5 which stops the compressor and at the same time takes away the voltage supply to the timing circuit RC. At this point the compressor is stopped and cannot be restarted until the torque drops down low enough for switch S.sub.1 to be reclosed which would then provide voltage to relay No. 1 through switch S.sub.3 which has reclosed since the voltage has been removed from relay No. 2 and it has gone back to its normally closed state.

With this circuit arrangement it is necessary that the torque continue at a predetermined high value for an uninterrupted time delay period which, as stated, is preferably about 75 seconds. Should there be any momentary decrease in the torque, the motor mount would swing away from switch S.sub.2 permitting the switch S.sub.2 to close and thereby ground the charge on the capacitor. This, then, means that subsequent reopening of switch S.sub.2 in response to the high torque will require initiation of the entire time delay period again. This system, therefore, is not additive of the periods that the torque may be above the predetermined high torque. The reason that the additive feature is not desirable is that as the ice builds up and the desired consistency is approached, there may be lumps or hard spots in the ice which cause momentary excursions in the torque load which are not truly indicative of the consistency. All other systems heretofore proposed for control of the slush consistency have, in effect, been additives. This statement would include those systems which use shock absorbers in controlling the movement of the motor. Those systems had no way to, in effect, cancel out the effect of momentary excursions in torque. The present system which requires a sustained torque in excess of the predetermined high gives a more accurate indication of the consistency. Once the refrigeration system is shut down, the consistency has to be reduced to that which permits reclosure of switch S.sub.1. If there is a period of heavy draw resulting in very rapid reduction in the consistency, this system will go back into operation much quicker than any of the prior devices which required a time delay subsequent to stopping the compressor. There is no fixed time delay with this arrangement and restarting of the compressor is dependent strictly upon consistency of the product.

Claims

I claim:

1. A slush machine including

a chamber adapted to contain liquid to be frozen to the consistency of slush,

a refrigeration system including a compressor and an evaporator surrounding the chamber for freezing liquid on the chamber walls,

a scraper rotatably mounted in the chamber to scrape ice from the chamber walls and including agitator blades,

a motor driving the scraper whereby the torque on the motor is an indicia of the consistency of the slush,

means responsive to an uninterrupted sustained torque of predetermined magnitude for a predetermined period of time to stop the compressor,

and means responsive to lower predetermined torque for any period of time to start the compressor.

2. A machine according to claim 1 in which the motor is mounted for rotation relative to the machine and including means biasing the motor to a first position corresponding to low torque, the torque load on the motor tending to rotate the machine against the bias of the biasing means.

3. A machine according to claim 2 in which the means to stop the compressor includes timing means which operates only while the predetermined torque obtains and which cancels the accumulated time if the torque falls below the predetermined magnitude before reaching said predetermined period.

4. A machine according to claim 3 in which the means for starting the compressor includes a switch which is actuated when the motor is in said first position,

said motor moving to a second position in response to torque of said predetermined magnitude,

and a second switch actuated when the motor is in said second position to energize the timing means.

5. A machine according to claim 4 in which said timing means operates to stop the compressor and to cancel the accumulated time in the timing means whereby the compressor may be restarted with no time delay.