MASTER/SLAVE COMPRESSOR CONTROL SYSTEM FOR REFRIGERATED VENDING MACHINES
Cross Reference To Related Application This application is related to copending U.S. patent application Serial No. 08/758,777, entitled, "Vending Machine Controller And System", filed on December 3, 1996, in the names of John Miller et al . This related application is assigned to the assignee of the present invention and is intended to be specifically incorporated herein by reference . Background of the Invention Field of the Invention
This invention relates generally to a method of feeding electrical power to a plurality of electrical apparatus, such as vending machines, so as to prevent power outages, and more particularly to a method of controlling the respective compressors of at least two refrigerated vending machines so that only one compressor operates at any one time. Description of Related Art
Processor-based vending machines are generally known and typically include one or more digital signal processors for controlling and monitoring vending machine operations. For example, in the above-related application Serial No. 08/758,777, there is disclosed, among other things, a vending machine including a vending machine controller (VMC) that incorporates a programmable microprocessor, a plurality of control and/or communication interfaces and an address and data buss system therefor. One of the interfaces comprises an input/output (I/O) interface through which the VMC controls, among other things, the vending mechanisms, and selection switches, door switches, service mode switches and alpha numeric displays. One other interface comprises a multi-drop buss (MDB) interface, through which the VMC communicates with various peripherals, such as coin mechanisms, credit card readers, bill validators, etc., transmit commands, and receive information from each of the peripherals in order to control a vending operation, typically through the I/O interface. The multi-drop buss or simply MDB is a standard communication buss used on many of the vending machines in the United States and throughout the rest of the world. Also, the vending machine controller is responsible for managing consumption of power by the vending machine and can disable one or more of the peripherals, if necessary, typically through the I/O interface.
While the concept of a vending system which includes a master vendor controlling the operation of one or more slave vendors is also generally known, a problem presents itself when more than one vending machine is needed, but there is insufficient power to run more than one refrigeration compressor at any one time or there is a limited number of power outlets. Summary
Accordingly, it is an object of the invention to provide an improvement in the interactive control between electrical apparatus so as to prevent power outages. It is a further object of the invention to provide an improvement in the interactive control between vendors in a master/slave vending machine system.
It is another object of the invention to provide a vending machine system where a plurality of vending machines can share a single power outlet. And it is yet a further object of the invention to provide an improvement in a refrigerated vending machine system whereby only one refrigeration compressor is permitted to operate at any one time. These and other objects are achieved by programming the microprocessors included in the respective vending machine controller (VMC) of at least two refrigerated vending machines so that they operate in a master and a slave relationship. In such an arrangement, the slave vendor VMC will only operate the compressor of its refrigeration unit when it is told to do so by the master. Communication between respective VMCs is by way of interconnection of their multi-drop buss (MDB) interfaces. The slave vending machine periodically sends a cabinet temperature reading of the vendor's cabinet to the master, whereupon the master VMC turns on the compressor of the warmest unit until its temperature drops and then operates the next warmest unit until all temperatures are within a desired range. In a preferred embodiment, AC power is supplied from a common wall outlet where it is applied to the respective compressors via electrically controlled switches. The switches are activated through respective input/output (I/O) interfaces coupled to respective programmable microprocessors and which are linked together via their MBDs.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. However, it should be understood that the detailed description and specific example, while indicating the preferred embodiment of the invention, is provided by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Brief Description of the Drawings
The present invention will become more fully understood when considered together with the accompanying drawings which are supplied only for purposes of illustration, and thus are not meant to be limitative of the present invention, and wherein:
Figure 1 is an electrical block diagram illustrative of the preferred embodiment of the invention; and
Figures 2A and 2B are flow charts which depict a method for controlling the apparatus shown in Figure 1.
Detailed Description of the Invention Referring now to the drawings wherein like reference numerals refer to like components throughout, reference numerals 10ι_ and IO2 denote two refrigerated vending machines capable of vending, for example, bottles or cans of a beverage and which are powered from a common outlet 12. While two vending machines are depicted in Figure 1, when desirable three or more vendors could be utilized where sharing of power outlets might be required. Often multiple vendors can't be placed in a particular location because there are not enough electrical outlets available and therefore the supplier must settle for one or two vending machines when the account volume could justify three or four.
Accordingly, the single wall outlet 12 is shown supplying power to both vending machines 10]_ and IO2.
Each unit is also shown being equipped with both a male AC plug 14]_ and 1 2anc^a female outlet 16]_ and
I62. Each plug and receptacle 14]_, 16η_ and 142, 1^2 are connected to a respective AC power buss 18]_ and 18 2 which supplies electrical power to all electric devices in the vendor.
In the embodiment shown in Figure 1, vending unit IO2 is powered from the same wall receptacle 12 as vending unit 10]_ by the connection of a heavy duty extension cord 20 between the female receptacle 16]_ of vending machine 10_ and the male plug 142 of the second vending machine IO2.
As shown, the AC busses 18]_ and I82 are adapted to supply electrical power to respective refrigeration compressors 24]_ and 242 located in the cabinet portions 25]_ and 252of tne vending units 10ι_ and IO2 via electrically controlled AC switches 26^ and 262.
Respective temperature sensors 28τ_ and 282 are located in the vending machines 10]_ and IO2 so as to monitor cabinet temperature, which is primarily influenced by the heat removed by its respective compressor 24]_ and
242.
Each vending machine 10τ_ and IO2, moreover, includes its own processor-based vending machine controller (VMC) 30]_ and 302, a typical example of which is shown in the above-referenced copending application Serial No. 08/758,777, and which includes, among other things, a locally or remotely programmable microprocessor 32]_ and 322, such as an Intel or Motorola Micro Controller. Also included in the VMCs 30]_ and 302 are respective address busses 34]_ and 3 2, data busses 36]_ and 362,an<^ input/output (I/O) interfaces 38],, and 382, each having output ports connected to respective vending machine control circuitry 40j_ and 402 and vending machine control system circuitry 42]_ and 422- While other elements are also included in each VMC 30]_ and 302, such as one or more random access memories, read only memories and read only memories, not shown, the VMCs 30]_ and 302 also include a well known multi-drop buss (MDB) interface 44j_ and 44 . Both I/O and MDB interfaces 38 i , 44]_ and 382, ^2 are connected to their respective programmable microprocessors 32j_ and 322,v"-a their respective address and data busses 34]_, 342,anci 361'
362.
Analog cabinet temperature signals are generated by the temperature sensors 28^ and 282 and are converted to digital signals in respective A/D converters 29]_ and 292 where they are then fed to the microprocessors 32^, 322v^-a the respective I/O interfaces 38]_ and 382 while control of the AC switches 26]_ and 262 is provided from the microprocessors 312, 322 through the respective I/O interfaces 38j_, 382an<^ the respective control circuitry 42χ, 422-
An important feature of this invention is that communication between the two vending machines 10]_ and
IO2 is provided by way of an interconnect cable 46 running between the MDBs 44]_ and 42- Another important feature is that the microprocessors 32]_ and
322 in Ah . VMCs 30]_ and 302 automatically sense when a plug has been inserted in the outlets 16]_ and I62 by way of an automatic sensing device, such as a switch shown, for example, by a switch 17]_ and 172 associated with the outlet lβ]_ and I62- The switches 17]_ and 172 are respectively connected to I/O interfaces 38]_ and 382- Alternatively, the microprocessors 32]_ and 322 can be configured to sense when another VMC has been connected directly through the interconnect cable 46. The microprocessors 32]_ and 322are programmed, either locally or remotely when interconnected so as to share a common AC power outlet, to operate in one of two modes, i.e. a master or slave, wherein one of the vending machines is caused to act as the master, while the other vending machine acts as the slave. With the interconnect cable 46 in place, the installer can designate which is the master and which is the slave. As shown, vendor 10]_ is designated the master, while vendor IO2 is made the slave. In the alternative, the VMCs 30]_, 302 could decide between themselves which is master or slave, once the MDBs 44]_ and 442are interconnected. The purpose of such a set up is that the slave controller 302 will operate its compressor 242only when it is told to do so by the master controller 30^. This means that the compressors of each vending machine 10]_ and IO2 never operate at the same time.
In the embodiment shown in Figure 1, the slave vending machine IO2 sends its cabinet temperature, as sensed by its temperature sensor 282, to the master vending machine 10ι_ every few seconds. This is achieved by the sensed temperature being fed to the slave microprocessor 322 which communicates to the master microprocessor 321_ by way of the interconnected MDBs 422an 21-If both cabinets 25]_ and 252are warmer than a predetermined setpoint, the master microprocessor 32]_ will turn on the compressor of the warmer unit either 24]_ or 242- Once that unit cools down below the temperature of the other vending unit, the master microprocessor 32]_ turns the first compressor off and operates the second compressor. While there would be some minimum run time to prevent short cycling of the compressors, basically they operate alternately back and forth so as to bring the two cabinet temperatures down together .
This type of operation is further shown by the flow charts of Figures 2A and 2B. Referring now to
Figure 2A, this simply is illustrative of the fact that a master and slave relationship between the vending machines 10ι_ and IO2 is initially established as shown by step 48. Next as shown by the flow chart in Figure 2B, following a start step 50, the processor 32]_ of the master VMC 30]_ determines whether the temperature Tm in the master cabinet 25^ exceeds the setpoint SP as shown by reference numeral 52. If an affirmative determination is made, the master processor 32ι_ next determines whether the temperature Tm exceeds the temperature Ts in the slave cabinet 252as shown by reference numeral 54. If the determination is affirmative, a command is generated to turn off the slave refrigeration compressor 242as shown by step
56. This is followed by a command to turn on the master refrigeration compressor 24]_ as shown by step
58, at which time the control sequence loops back to start step 50. On the other hand, if a determination is made in step 52 that Tm is less than Ts, then a command is generated by the master processor 32]_ to turn off the master compressor 24]_ as shown by step 60, whereupon a query is made as to whether or not the temperature Ts in the slave cabinet 252 is greater than the setpoint
SP. This is shown by reference numeral 62. If the determination is affirmative, then a command is generated to turn on the slave compressor 24 as shown by step 64, whereupon the control sequence loops back to the start step 50. If the determination in step 62 is in the negative, then a command is generated by the master processor 32]_ to turn off the slave compressor 242as shown by step 66 and the control sequence again loops back to the starting step 50. Thus a continual looping type of control strategy is employed to regulate both cabinet temperatures .
Such an operation has the effect of preventing power overloads which could occur if both refrigeration compressors 24]_ and 242 were allowed to be on at the same time, when powered from the same power line. While this type of control is particularly useful for vending machine operations where more than one vending machine is necessary in a particular location but there is limited access to more than one power line or where there is insufficient power to run more than one compressor at once, it is particularly important where a single outlet is able to supply power for the lights and electronic circuits for a plurality of vending machines, but is incapable of supplying power to more than one compressor simultaneously.
Accordingly, such a control strategy can have a wide field of applications, and therefore the foregoing description should not be interpreted as being limited to vending machine systems, since this same strategy can be employed to cover any application where coordination is necessary between electrically powered devices requiring relatively large amounts of electrical power and in order to prevent power outages .
Having thus shown and described what is at present considered to be the preferred embodiment of the invention, it should be noted that the same has been made by way of illustration only, and that all alterations, changes and modifications coming within the spirit and scope of the appended claims are herein meant to be included.