According to one embodiment, an arm structure includes a base, a first link, a second link, a connecting member, and a gravity compensation mechanism. The first and the second links are rotatable in a vertical direction. One end side of the first link is pivotally attached to the base via a first rotating shaft. One end side of the second link is pivotally attached to another end side of the first link via a second rotating shaft. A length of the first link is same as a length of the second link. The second link rotates around the second rotating shaft. A rotation angle of the second link is twice a rotation angle of the first link. A rotation direction of the second link is opposite to a rotation direction of the first link. The gravity compensation mechanism compensates for torque generated around the first rotating shaft by gravity.

The utility belongs to the field of the non-beam pumping unit, specifically relating to a single motor non-beam pumping unit with a reducer built in the roller. The single motor non-beam pumping unit with a reducer built in the roller comprises a base, a tower body and a drive mechanism. The upper end of the tower body is provided with a platform and the drive mechanism is mounted on the platform. The drive mechanism comprises a motor, a reduction mechanism, a roller and a belt. According to the utility, the reduction mechanism is built in the roller, so that the damage to the reduction mechanism caused by the natural environment such as wind, rain and sun can be avoided, thus extending the service life and maintenance cycle of the reduction mechanism and improving the stability of operation of the device.

According to one embodiment, an arm structure includes a base, a first link, a second link, a connecting member, and a gravity compensation mechanism. The first and the second links are rotatable in a vertical direction. One end side of the first link is pivotally attached to the base via a first rotating shaft. One end side of the second link is pivotally attached to another end side of the first link via a second rotating shaft. A length of the first link is same as a length of the second link. The second link rotates around the second rotating shaft. A rotation angle of the second link is twice a rotation angle of the first link. A rotation direction of the second link is opposite to a rotation direction of the first link. The gravity compensation mechanism compensates for torque generated around the first rotating shaft by gravity.