Food service system utilizing reflected infrared signals to identify type of dish

Abstract

In a food service system, prepared meals including chilled foods are assembled in individual meal trays (10) and held in the trays for a period prior to regeneration to prepare the food for heating. A control system of a rethermalizing trolley (12), which accommodates a large number of trays, can discern for itself which dishes (30) in the trays need heating and which are to remain cool. Dishes for hot and cold foods have white and black markings respectively, which results in reflected infra-red signals from sensors (42, 44) of the control system to be of discernably different strengths, so identifying the hot food dishes. Dish temperature is continually monitored by the control system by means of thermal contact with thermistors (46), which enables the system to oversee food temperatures both prior to and during regeneration.

We claim: 
     
       1. For use in a food service system in which prepared meals including chilled foods are assembled in individual meal trays and held in the trays for a period prior to regeneration in the trays to prepare the food for eating, rethermalizing apparatus comprising: (i) a meal tray forming a plurality of compartments in which removable food dishes can be located;   (ii) dish-heating means comprising a plurality of heating units which for effecting thermalization are positioned beneath food dishes in said compartments in said tray and are independently operable for selective heating or non-heating of said dishes as required;   (iii) food dishes of a first type (hot food dishes) which can be located in said compartments in said tray to hold food which is to be heated;   (iv) food dishes of a second type (cold food dishes) which can be located in said compartments in said tray to hold food which is to remain unheated;   (v) heating control means operative to activate said heating units selectively so as to heat any hot food dish located thereover in said tray but not to heat any cold food dish located thereover;   said control means comprising a plurality of sensor units which are associated one with each of said heating units to reflect radiated sensing signals off dishes in said compartments in said tray and to respond to the reflected signals, said hot food dishes and said cold food dishes being distinctive as to the signals caused to be reflected from them whereby enabling the control means to distinguish between them for operation of those heating units alone positioned beneath hot food dishes.   
     
     
       2. Apparatus according to claim 1 characterized in that the sensing signals are of infra-red radiation. 
     
     
       3. Apparatus according to claim 1 characterized in that it comprises a rethermalizing trolley having a plurality of shelves on which trays can be lodged, each shelf comprising a plurality of heating units which are arranged to be in registry with the dishes in a tray installed on the shelf in order to heat those dishes if required. 
     
     
       4. Apparatus according to claim 1 in which said heating units comprise thermally conductive heating plates and electric heating elements for heating the plates. 
     
     
       5. Apparatus according to claim 4 in which there are openings in said heating plates for said sensor units to reflect sensing signals off dishes thereabove. 
     
     
       6. Apparatus according to claim 5 in which said sensor units are mounted in said openings within said heating plates. 
     
     
       7. Apparatus according to claim 5 in which each sensor unit comprises an infra-red emitter and an infrared detector which are potted together in a casting resin and mounted within said opening. 
     
     
       8. Apparatus according to claim 7 in which each sensor unit comprises also a thermistor which is potted together with said emitter and said detector, an uppermost edge of said thermistor being coincident with a top surface of the unit and said top surface being flush with an upper surface of said heating plate.