Lifting column with low retracted height

A lifting column with low retracted height, the lifting column comprising:

• a drive unit, a lifting tube, and a transmission assembly disposed in the lifting tube, wherein the lifting tube comprises a first tube, a second tube, a third tube, a fourth tube, and a fifth tube, which are sequentially nested from inside to outside, a lower end of the fifth tube is secured on the drive unit;
• the transmission assembly comprises a first screw rod, a hollow second screw rod, a hollow third screw rod, and a hollow fourth screw rod, which are nested sequentially from inside to outside, an output end of the drive unit is in transmission fit with the first screw rod and configurable to drive the first screw rod to rotate;
• and a lower end of the second screw rod is provided with a first nut in threaded transmission connection with the first screw rod, a lower end of the third screw rod is provided with a second nut in threaded transmission connection with the second screw rod, a lower end of the fourth screw rod is provided with a third nut in threaded transmission connection with the third screw rod, and a lower end of the first tube is provided with a fourth nut in threaded transmission connection with the fourth screw rod,
• an upper end of the first screw rod is provided with a first guide sleeve that limits an axial position of the first nut, an upper end of the second screw rod is provided with a second guide sleeve that limits an axial position of the second nut, an upper end of the third screw rod is provided with a third guide sleeve that limits an axial position of the third nut, and an upper end of the fourth screw rod is provided with a fourth guide sleeve that limits an axial position of the fourth nut,
• an outer wall of the first guide sleeve is fitted with an inner wall of the second screw rod, an outer wall of the second guide sleeve is fitted with an inner wall of the third screw rod, an outer wall of the third guide sleeve is fitted with an inner wall of the fourth screw rod, and an outer wall of the fourth guide sleeve is fitted with an inner wall of the first tube.