the bottom structure for a bed of the present invention is described below in reference to the attached drawings . fig1 shows a bed 1 , to which the bottom structure of the present invention is applied . the bed 1 can have the bottom 2 lifted at the back and knee portions by an electric actuator 3 provided below the bottom 2 . the actuator 3 is provided with back lifting arms 4 for lifting the back portion and knee lifting arms 5 for lifting the knee portion . the back lifting arms 4 contact the bottom 2 on the underside at the portion corresponding to the back portion , through rollers 6 , and the knee lifting arms 5 contact the bottom 2 on the underside at the portion near the patient &# 39 ; s knees , through rollers 7 . in the bed 1 , flexible hollow bottom members 8 are provided at the bendable portion between the back and waist portions of the bottom 2 and at the portion corresponding to the patient &# 39 ; s knees . the flexible hollow bottom members 8 are preferably formed to be hollow and zigzagged on the upper and lower surfaces , using a blow molded thermoplastic resin ( see fig2 and 3 ). in the bed 1 with the above bottom structure , when the actuator 3 is started to lift the back and knee portions , the flexible hollow bottom members 8 are bent , being contracted on the upper side and extended on the underside , so that the bottom 2 may be bent to form an overall gentle curve ( see fig2 ). since the flexible hollow bottom members 8 are located at any bendable position and are not sharply bent , but rather bent in a larger radius of curvature , the adjustment of the angle of bend is not required . when the bottom is lifted at the back and knee portions , the bent portions form a gentle curve as a result of the flexible hollow bottom members 8 . therefore , the waist , abdomen , and underside of the patient &# 39 ; s legs at the bent portions are not uncomfortably pressed by the mattress . the flexible hollow members 8 are single parts made using blow molded thermoplastic resin which is an advantage in view of manufacturing costs . the bottom 2 can be completely assembled simply by connecting the flexible hollow bottom members 8 between the ordinary bottom portions 2 corresponding to the back , waist and legs of the patient . therefore , the number of assembling steps can be small . furthermore , since they are hollow parts made of a thermoplastic resin , they are bendable , extensible , and light weight . moreover , since the bottom 2 can be formed as a seamless whole , cleaning is easy . as described above , the present device has the following effects : 1 . since the bottom structure is provided with bendable and extensible flexible hollow bottom members , it can be lifted at the back and knee portions without causing any displeasing pressure . 2 . since the flexible hollow bottom members are comprised of single parts formed by blow molding of a thermoplastic resin , they can be manufactured at a low cost and can reduce the number of steps of assembly . 3 . since the flexible hollow bottom members are hollow , they provide a bottom structure of reduced weight .
the present invention provides a bottom structure for a bed having a bottom lifting mechanism , comprising bendable and extensible flexible hollow bottom members , provided in the bottom structure allowing the bottom to be bent .