Harmonic drive with compact structure made by plastic material

A motorized harmonic drive comprising:

• an outer shell, the outer shell housing
• i) a circular spline, rigid, internally toothed;
• ii) a flex spline, flexible and elastically deformable, externally toothed, meshed and configured to cooperate with said circular spline to transmit motion in the motorized harmonic drive;
• and
• iii) a wave generator configured to rotate around a longitudinal axis of the motorized harmonic drive;
• and
• an electric motor, also housed in said outer shell, for driving rotation of said wave generator around the longitudinal axis of the motorized harmonic drive,
• wherein the wave generator is configured to engage directly, in diametrically opposite areas of the same wave generator, an internal surface of the flex spline to elastically deform the flex spine and press its external toothing against an internal toothing of the circular spline, when the wave generator rotates around the longitudinal axis of the motorized harmonic drive;
• wherein said flex spline has an externally toothed belt shape, with an internal surface and an external toothing;
• wherein said circular spline is a double circular spline and comprises a first circular spline, fixed to the outer shell, and of a second circular spline, connectable to an external entity which receives and is driven at a reduced angular speed produced by the motorized harmonic drive, each of said first circular spline and said second circular spline having a respective internal toothing;
• wherein said second circular spline is configured to rotate around said longitudinal axis at a reduced angular speed with respect to the rotation, controlled by said electric motor, of said wave generator;
• wherein the internal toothing of the first circular spline, fixed to the outer shell, has a number of teeth equal to that of the external toothing of the flex spline, and the internal toothing of the second circular spline, connectable to the external entity, has more teeth, in particular two, compared to those of the internal toothing of the first circular spline;
• wherein the external toothing of the flex spline is meshed half with the internal toothing of the first circular spline and half with the internal toothing of the second circular spline;
• wherein the wave generator comprises at least a first rotating bearing and at least a second rotating bearing arranged in diametrically opposite areas of the same wave generator, which bearings, when the wave generator rotates around the longitudinal axis of the motorized harmonic drive, engage an internal surface of the flex spline to elastically deform the flex spine and therefore press one half of its external toothing against the internal toothing of the first circular spline and another half against the internal toothing of the second circular spline;
• whereby, in the operation of the motorized harmonic drive, when the wave generator rotates around said longitudinal axis, an angular phase shift between the first and the second circular splines of the circular spline, due to the difference between the number of the teeth of the two internal toothings of the first circular spline and of the second circular spline, causes an elastic deformation of the flex spline, engaging with the first circular spline under the pressure exerted by the wave generator on the internal surface of the flex spline, and forces the second circular spline to align with the first circular spline in at least two meshing areas, diametrically opposite each other, between the flex spline and the second circular spline;
• wherein the wave generator has a first double row and a second double row of rotating bearings, arranged in diametrically opposite areas of the same wave generator, including respectively said at least one first rotating bearing and said at least one second rotating bearing;
• wherein the first double row and the second double row of rotating bearings are suitable for engaging the internal surface of the flex spline to elastically deform the flex spine and thereby press respectively one half of its external toothing against the internal toothing of the first circular spline and another half of its external toothing against the internal toothing of the second circular spline;
• wherein the wave generator is rotatably mounted on said first circular spline with interposition of one or more ball bearings;
• wherein the flex spline, externally toothed, is housed in an annular space formed by the first circular spline, by the second circular spline, and by the wave generator;
• and
• wherein said electric motor has a stator, fixed to said outer shell, and a rotor, fixed to the wave generator, to drive its rotation around the longitudinal axis of the motorized harmonic drive.