Article by Dr. Eric Sheu

"Servo motor" is the power device most widely adopted in the machinery in the industry. The transmission performance of an industrial machine is basically determined upon the output characteristics of the servo motor, and the positioning function of the servo motor directly affects the accuracy of the motion of the machine. The speed control function will also affect the stability of the motion. Therefore, precise positioning and smooth speed control are the prerequisite for a servo drive.

“Permanent magnet AC servo” was officially launched in the market in 1990. However, with CPU of low speed, the drive could only complete simple functions by analog components. Today, PM AC servo has become essential in the machinery requiring high accuracy, e.g. CNC machine tools and semiconductor related equipment for its small size, high efficiency, fast responding speed and high accuracy.

Due to that “AC servo” is the power source to drive automation equipment, machine tool and general industrial machines, industrialized countries as the United States, Germany and Japan pay very much attention to the development of the AC servo. In brief, the high-grade AC servo motor and drive have to adopt the following technology:

•  High-MGOe PM material, allowing the motor efficiency to exceed 85%.

•  Computer-aided design software to speed up the development time and enhance the output characteristics of the motor.

•  The sine interpolation makes the resolution of the encoder exceed 17 bits.

•  The drive devices are IGBT and IPM. The control circuit conducts digitalization, and the control performance and system stability will therefore be further refined.

•  The vector control theory is realized by high-speed DSP, and meanwhile the responding bandwidth of current loop is extended to 2KHz. The speed loop can also be set up to 500Hz. The load inertia measurement, output power overload ratio and resonance suppression filter are included in the firmware program.

Delta started to develop AC motor drives since 1995. Over years of devotion, we now sell the most AC motor drives among other competitors in Taiwan. In 2004, we launched the first-generation A series servo drive and has gradually built up our reputation in the market. In order to offer our clients more complete and functional products, we currently developed the 20-bit encoder with the big-horsepower ASDA-A+ series products. ASDA-A2 series servo drive with high-speed communication and the servo motor with 20-bit encoder will be launched in the beginning of 2008. ASDA-A2 series will be able to control many 20-bit servo motors by a single high-speed communication cable, which is easy to wire and will create outstanding performance.