Electromagnetic drive spherical robotic wrist with two degrees of freedom and control method therefor

An electromagnetic drive spherical robotic wrist with two degrees of freedom, comprising a three axis Helmholtz coil assembly (a) and a rotor following unit (b), wherein the three axis Helmholtz coil assembly (a) provides a spatial universal rotational magnetic field, and the rotor following unit (b) provides pitch and yaw rotation with two degrees of freedom under the drive of a coaxial following magnetic torque of the rotational magnetic field;

• the rotor following unit (b) comprises an internal cross universal joint (d), an external cross universal joint (c) and a fixed end (e);
• the fixed end (e) is provided with a fixed end support seat (5) at the top, the fixed end support seat (5) is divided into four vertical support frames on the same axis, the support frames are provided with horizontal holes, the two vertical support frames in the middle are used for installing the internal cross universal joint (d), and the two vertical support frames on outer ends are used for installing the external cross universal joint (c);
• the internal cross universal joint (d) comprises the two vertical support frames in the middle of the fixed end support seat (5), an internal universal joint inner ring (14) and a cylindrical case (2), wherein the internal universal joint inner ring (14) is used as a cross shaft bracket, and the cylindrical case (2) is used as a driven fork;
• both sides of the internal universal joint inner ring (14) are respectively installed in the holes of the two vertical support frames in the middle of the fixed end support seat (5) by a deep groove ball bearing a (15) and a deep groove ball bearing b (16), and the fixed end support seat (5) and the internal universal joint inner ring (14) realize relative rotation, forming a pitching rotating shaft;
• the cylindrical case (2) is located in the internal universal joint inner ring (14), a connecting shaft d (23) and a connecting shaft e (26) are respectively symmetrically fixed on both sides of the cylindrical case (2) at one end, and are respectively installed on the inner side of the internal universal joint inner ring (14) through a deep groove ball bearing c (24) and a deep groove ball bearing d (25) at the other end, and the cylindrical case (2) and the internal universal joint inner ring (14) realize relative rotation, forming a yawing rotating shaft;
• a permanent magnet cylinder with radial magnetization (1) is installed in the cylindrical case (2) through a bearing (31);
• the external cross universal joint (c) comprises the two vertical support frames on outer ends of the fixed end support seat (5), an external universal joint inner ring (3) and an external universal joint outer ring (17), wherein the external universal joint inner ring (3) is used as a cross shaft bracket, the external universal joint inner ring (3) is symmetrically provided with four coaxial horizontal holes, and the external universal joint outer ring (17) is used as a driven fork;
• a connecting shaft a (7) and a connecting shaft b (9) are respectively installed in the holes of the two vertical support frames on outer ends of the fixed end support seat (5) by a flange bearing a (8) and a flange bearing b (10);
• the coaxial holes on two sides of the external universal joint inner ring (3) are respectively fixedly connected to the connecting shaft a (7) and the connecting shaft b (9) through a general flat key a (6) and a general flat key b (11), and the fixed end support seat (5) and the external universal joint inner ring (3) realize relative rotation, forming a pitching rotating shaft;
• the connecting shaft a (7) is connected to an encoder a (4) at the outer end, the connecting shaft b (9) is connected to an damper a (12) at one end and is connected to a brake a (13) at the other end, and the encoder a (4), the damper a (12) and the brake a (13) are all fixed on the fixed end support seat (5);
• a connecting shaft c (21) and a connecting shaft f (28) are respectively installed in the coaxial holes on the other two sides of the external universal joint inner ring (3) through a flange bearing c (22) and a flange bearing d (27);
• the external universal joint outer ring (17) is symmetrically composed of two support rods with a semi-annular structure, the two support rods are respectively fixedly connected to the connecting shaft c (21) and the connecting shaft f (28) through a general flat key c (20) and a general flat key d (29) at one end, the ends of the support rods are located outside the external universal joint inner ring (3), and the two support rods are fixed on both sides of an output end (33) at the other end;
• the external universal joint outer ring (17) and the external universal joint inner ring (3) realize relative rotation, forming a yawing rotating shaft;
• a connecting rod (32) is fixed on the top of the cylindrical case (2) at one end, and is fixedly connected to the output end (33) at the other end;
• the connecting shaft c (21) is respectively connected to an encoder b (18) and a brake b (19) at both ends, the connecting shaft f (28) is connected to a damper b (30) at the outer end, and the encoder b (18), the brake b (19) and the damper b (30) are all fixedly fixed on the outer side of the external universal joint inner ring (3);
• on the premise that two input ends of the external cross universal joint (c) and the internal cross universal joint (d) are coaxially connected, two output ends of the external cross universal joint (c) and the internal cross universal joint (d) are coaxially connected to form the rotor following unit (b) of the wrist, the external cross universal joint (c) and the internal cross universal joint (d) have the same rotation center, so that a spherical wrist is formed, motion decoupling with two degrees of freedom of the wrist is realized, and yaw and pitch angles can be measured and controlled separately, the encoder a (4), the brake a (13) and the damper a (12) respectively realize the functions of measuring, braking and changing damping characteristics of pitch rotation, the axis of the rotor following unit (b) is a wrist rotation axis, which realizes fixed point pitch and yaw rotation with two degrees of freedom, and the permanent magnet cylinder with radial magnetization (1) realizes fixed point pitch and yaw rotation with two degrees of freedom of the wrist under the drive of the coaxial following magnetic torque of the spatial universal rotational magnetic field;
• and
• the three axis Helmholtz coil assembly (a) comprises a large coil assembly, a small coil assembly and a middle coil assembly, and each assembly comprises two identical coils which are arranged symmetrically;
• axes of the three coil assemblies are perpendicular to each other, and the three coil assemblies are fixed to each other, wherein the large coil assembly is fixed on the fixed end (e) at the bottom, and the axis of the middle coil assembly is coincident with the axis of the fixed end (e);
• the internal cross universal joint (d) is located in an internal space in the center of the three coil assemblies, and the external cross universal joint (c) is located outside the three coil assemblies;
• the external cross universal joint (c), the three axis Helmholtz coil assembly (a) and the internal cross universal joint (d) spatially form a three layers nested structure.