Electrically adjustable bed

An adjustable bed comprising:

• a plank assembly comprising a first waist plank and a second waist plank;
• a frame;
• a power unit pivotally connected to the frame;
• a support assembly comprising a waist-lifting unit comprising a first lifting element pivotally connected to the frame, a second lifting element pivotally connected to the frame, and a transmission unit comprising:
• a shaft operatively connected to the power unit;
• two rocking levers connected to the shaft so that they can only be rotated together;
• two swinging levers connected to the shaft at an end so that they can only be rotated together and pivotally connected to the frame at another end;
• two primary levers each pivotally connected to a corresponding one of the rocking levers;
• two secondary levers each connected to a corresponding one of the primary levers at an end and connected to the frame at another end;
• two arched elements;
• a movable element comprising a first crossbar connected to the arched elements so that they can only be moved together, two longitudinal bars pivotally connected to the first crossbar, and a second crossbar pivotally connected to the longitudinal bars;
• and
• two linkages each for connecting the frame, a corresponding one of the arched elements and the first and second lifting elements to each other;
• wherein when the power unit is at a minimum value of length, the waist-lifting unit is laid horizontally, the first waist plank is supported on the first crossbar of the movable element, and the second waist plank is supported on the second crossbar of the movable element and abutted against the frame;
• wherein when the power unit extends, the swinging levers swing and hence move the rocking levers, and each of the secondary levers changes an angle between the corresponding primary lever and the corresponding arched element, thereby lifting the movable element and the first waist plank, abutting the second waist plank against the arched elements, and lifting the arched elements so that the first and second lifting elements are tilted relative to the frame;
• wherein the linkages keep the arched elements horizontally when the arched elements are lifted so that the first and second lifting elements are tilted by substantially identical angles relative to the frame.