Scara Robot

The first SCARA robot was created as a revolutionary prototype in 1978, in the laboratory of Professor Hiroshi Makino, at Yamanashi University in Japan. The 4-axis SCARA was designed as no other robot arm at the time. Its simplicity was brilliant … with less motion it could do more, with high speed and precision.

The acronym SCARA stands for Selective Compliance Assembly Robot Arm. The robots themselves may vary in size and shape but all SCARA arms are consistent in a unique 4-axis motion. SCARA excels in “pick and place”… in its unique ability to pick up industrial components from one location and place them in another, with precision, speed, and smooth motion.

The SCARA arm behaves somewhat like the human arm in that joints allow the arm to move vertically and horizontally. However, the SCARA arm has limited motion at the wrist; it can rotate but it cannot tilt. The limited motion of the wrist is advantageous for many types of assembly operations, such as pick-and-place, assembly, and packaging applications.

SCARA robots were introduced to commercial assembly lines in 1981 and still offer the best price/performance ratio regarding high speed assembly. The Japanese flexible assembly system, based on the SCARA robot, created a worldwide boom in small electronics production, creating products which drove the economy and changed the world forever.

 

This robot has vertical joints so that none of the major joints moves vertically removing gravity from the movement equation.   They are ideal for fast assembly operations on the factory floor.   The robot is controlled by stepper motors which are digital motors directly controlled from the computer and having no feedback.  Each computer impulse is delivered via step up voltage to the motors multiple internal coils and usually gives a step of about 7.5 degrees.    A rapid sequence of pulse gives continuous jerk free motion.  Speed can be ramped up and down to take care of inertia in the mechanical system and loads.    Prevention of digital slippage depends on the applied power to the coils.

This model will soon become a ModelPlan with full computer control from a set program which can be used to teach the robot to perform a set of movements and repeat them with unbelievable accuracy and repeatability. 

Michael Adler

June 2008.