Design studies on cellular structures with pneumatic artificial muscle inclusions for modulus variation

This article presents a variable modulus cellular structure based on a hexagonal unit cell with pneumatic artificial muscle inclusions. The cell is pin-jointed, loaded in the horizontal direction, with three pneumatic artificial muscles (one vertical pneumatic artificial muscle and two horizontal pneumatic artificial muscles) oriented in an “H” configuration between the vertices of the cell. A method for calculation of the hexagonal cell modulus is introduced, as is an expression for the balance of tensile forces between the horizontal and vertical pneumatic artificial muscles. Simulation is then compared to experimental measurement of the unit cell modulus in the horizontal direction over a pressure range of 682 kPa, and an increase in cell modulus of 200% is demonstrated experimentally. A design study considering parametric variation in cell angle, vertical to inclined wall length ratio, and pneumatic artificial muscle contraction ratios shows that changes in modulus of over 1000% are possible when the pneumatic artificial muscles are pressurized to 1992 kPa. This concept provides a way to create a structural unit cell whose in-plane modulus can be tuned based on the orientation of pneumatic artificial muscles within the cell and the pressure supplied to the individual muscles.