C. W. Musser

C. W. Musser
Patented strain wave gearing 1955

The unique principle of strain wave gearing, the technology used in our Harmonic Drive® gears, was the brainchild of the American inventor Clarence Walton Musser. Musser was a brilliant inventor who was awarded more than 200 patents, in a wide range of fields going even beyond his specialty in mechanical engineering to include physics, chemistry, and biology. C. Walton Musser studied and researched non-rigid body mechanics using controlled deflection as an operating medium. The basic principle of the strain wave gear was first announced in 1957, patent Number 2,906,143 which covers a "... motion transmitting mechanism".

Prior to his invention, efforts to achieve greater speed and accuracy in gear mechanisms for conveying driving power and motion were focused solely on making the gear mechanism more rigid. The principle of the harmonic gear, by contrast, was to make use of the flexibility of metal and apply elastic dynamics. Since this method of conveying motive power turned conventional wisdom on its head, it suddenly became the object of worldwide interest.

This unique gear mechanism provides zero backlash for the life of the gear, delivers high torque with high accuracy, in a compact light weight package. A wide range of gear reduction ratios can be achieved without changing the weight, size or form factor of the gear.

Strain wave gears are currently manufactured under the brand name Harmonic Drive® by companies in the US, Japan and Germany.

Clarence Walton Musser was born in Lancaster Pennsylvania in 1909. Walton Musser graduated from Manheim Borough Public High School in 1926. He was a registered Engineer in the States of Pennsylvania and Massachusetts. Having served as certified engineer in the states of Pennsylvania and Massachusetts, Musser polished his skills at many universities including M.I.T. and the University of Pennsylvania, then went on to become a professional inventor, forming consultancy contracts with the U.S. Government and a number of companies such as General Motors, Olin Mathieson, and United Shoe Machinery. Mr. Musser died on June 8, 1998.

During World War II, Musser's efforts paid off in the invention of the recoilless rifle. This invention was awarded 61patents, and Musser personally oversaw its manufacture and prototype testing. Around the same period Musser developed many safety devices for aircraft including a cartridge driven catapult, canopy jettison system, and parachute release device.

After the war, Musser went on to become the pioneer in the field of mechanics actively introducing elastic deformation. He was awarded more than 70 patents in 15 countries for the strain wave gear mechanism. Among his other accomplishments are plastic products and elaborate testing and measuring equipment. His patents in the U.S. number more than 200, and many more of his patents have been announced in at least 28 countries.

Mr. Musser's life work and achievement can best be expressed by his philosophical statement, “It is never a question as to whether it can be done - it is only whether one cares to spend the time and effort."

The Musser Heritage Room

Upon Walt’s passing, his wife, Edna Musser, proudly donated the contents of his lab to Harmonic Drive in 2001. In 2006, a Musser Heritage Room was opened in the Hotaka Plant site (Azuminoshi,Nagano Prefecture) with exhibits relating to C. W. Musser. The items on display include machine tools and measurement instruments actually used by Musser, his papers, patent materials and prototypes around the time he invented the strain wave gear, and other objects, which were presented to HDSI thanks to the kindness of his surviving family. The entranceway arch, the wooden furniture in the hall, and the fixtures adopt a design modeled after his home laboratory.

 

Harmonic Drive® Gears

Utilizing the elastic dynamics of metal, Harmonic Drive® gears consists of just three basic components: a wave generator, flexspline, and circular spline.

Wave Generator

The Wave Generator is comprised of a specially designed thin raced ball bearing that is fitted onto an elliptical hub. This serves as a high efficiency torque converter and is used as the input of the gear and is connected to the motor shaft.

Flexspline

The Flexspline is a thin cylindrical cup made from alloy steel with external teeth on the open end of the cup. The Flexspline is radially compliant but torsionally is very stiff. When the Wave Generator in inserted into the Flexspline the gear takes on its elliptical shape. The Flexspline is used as the output and is connected to the output flange.

Circular Spline

The Circular Spline is a rigid ring with internal teeth. When the gear is assembled it engages the teeth of the Flexspline across the major axis of the Wave Generator ellipse. The Circular Spline has two more teeth than the Flexspline and is fixed to the gear housing.