Playpen hub assembly and playpen using the same

A playpen, comprising:

• a frame comprising:
• an arm frame comprising a plurality of top corners;
• and
• a plurality of standing posts, each connecting to the arm frame via one of the top corners;
• and
• a playpen hub assembly, comprising:
• a base seat;
• a first bottom pipe, a second bottom pipe, a third bottom pipe, and a fourth bottom pipe, each pivoting to the base seat with one end and pivoting to the bottom of corresponding standing post with the other end respectively wherein the bottom pipes are configurable to an unfolding position or a folding position relative to the base seat;
• a linking device pivoting to the first bottom pipe and the second bottom pipe with the linking device's two ends and moveable with the first bottom pipe and the second bottom pipe, the linking device configurable to a first position and a second position relative to the base seat when the first bottom pipe and the second bottom pipe are configured to the unfolding position and the folding position respectively, the linking device comprising:
• an engaging component, wherein the base seat comprises a groove and the engaging component comprises a protrusion for sliding vertically in and along the groove, thereby restricting movement of the engaging component in a direction when the linking device moves between the first position and the second position along with the first bottom pipe and the second bottom pipe;
• and
• a first pivoting component pivotally connected to the first bottom pipe at a first end of the first pivoting component for pivoting with respect to the first bottom pipe, and pivotally connected to the engaging component at a second end of the first pivoting component for pivoting with respect to the engaging component;
• and
• a second pivoting component pivotally connected to the second bottom pipe at a first end of the second pivoting component for pivoting with respect to the second bottom pipe, and pivotally connected to the engaging component at a second end of the second pivoting component for pivoting with respect to the engaging component;
• a locking device configured at the base seat abutting against the engaging component of the linking device to secure the linking device at the first position for securing the first bottom pipe and the second bottom pipe at the unfolding position, wherein a plane including the first bottom pipe, the second bottom pipe, the first pivoting component, and the second pivoting component is parallel to a pivot axis about which the locking device rotates when the locking device engages with and disengages from the engaging component;
• and
• an elastic component disposed between the base seat and the locking device and biasing the locking device against the engaging component.