Development and application of nutation motors

Introduction

 Nutation motors are new types of stepping motor, which have been jointly developed with our laboratory and TOK BEARING CO.,LTD. jointly. These motors have high resolution, speed reduction function, and overload protecting function. They can also be used in various environments due to their heat resistance, water resistance, dust resistance, and explosion proof. (Pneumatic nutation motor can be used even in strong magnetic fields.) Additionally, controlling valves decides rotation speed and rotation angle, therefore the feedback from sensors are not necessary. In our laboratory, two types of nutation motors; pneumatic nutation motor and electric nutation motor, have been developed.

                         
         Fig.1 φ10,φ20 Pneumatic Nutation Motors      Fig.2 φ50 Pneumatic Nutation Motor

Structure and driving principle

  The φ50 pneumatic nutation motor consists of three parts, pneumatic pistons, an input bevel gear, and an output bevel gear. The sequential pressures of three pneumatic pistons cause nutation motion of the input bevel gear. The teeth of the output bevel gear is one fewer than that of the input bevel gear, therefore one nutation motion causes rotation of one tooth in reverse.

In the year 2004, pneumatic nutation motor was improved structurally for miniaturization. Its pneumatic pressure direction was turned from axial to radial. Therefore the pneumatic nutation motor was miniaturized up to 10 mm in a diameter.

By comparison, in electric nutation motor, electromagnets serve as pneumatic pistons.

               
                                Fig.3　Structure of φ50 Pneumatic Nutation Motor


                                      
                                  Fig.4 Structure of φ10 Pneumatic Nutation Motor


                   
                                       Fig.5 Structure of Electric Nutation Motor

                      Table.1 Specification of three nutation motors

Robot hand as an application of φ10 pneumatic nutation motors

 The φ10 pneumatic nutation motor has these characteristics, short length, low speed and high torque output due to its speed reduction function. Additionally, overload protecting function can protect physical objects and devices. To utilize these characteristics, a robot hand was developed as an application. It consists of 23 motors at every joint directly. One motor needs 3 bits signal to rotate, therefore solenoid valves are controlled by 69 bit signals in total to operate the robot hand.

                                 Fig.6 Robot hand with 23 Pneumatic Nutation Motors

Conclusions

Nutation motors have various characteristics, high resolution, speed reduction function, overload protecting function, and free / locked modes of output shaft. They can also be used in various environments due to their heat resistance, water resistance, dust resistance, and explosion proof. (Pneumatic nutation motor can be used even in strong magnetic fields.) Therefore nutation motors are expected to be used in wide range of fields; industry, livelihood, medicine, etc.

History of nutation motors

2001      Development and application of nutation motors

l         Pneumatic nutation motor : Confirmation of motion with a prototype model

l         φ50 pneumatic nutation motor : Measurement and control

l         Development of pneumatic nutation motor by self-oscillation drive

l         6 DOF parallel link robot : Development and control

2002            Development of electric nutation motor

l         Electric nutation motor : Analysis, design, manufacture, and control

O         Design of electric solenoids : Magnetic field analysis and measurement by finite element method

O         Development of motor driver

2003            Application of φ50 Pneumatic nutation motors

l         A serial link robot : Design, manufacture, and control

2004            Miniaturization and application of pneumatic nutation motor-

l         φ10 Pneumatic nutation motor : Measurement

l         Robot hand : Design, manufacture, and control