the cam 118 engages the pivot linkage 104 to move the platen roller 24 from the nonprinting position to the printing position and to engage and disengage the drive gear 106 with the stationary gear 114 a spring 121 wrapped around one end of the pin 112 biases the linkage 104 against the cam 118 to bias the pivot linkage 104 away from the platen roller printing position the cam 118 is fixed to a cam shaft 120 which is rotated about a cam shaft axis 113 by the lever 50 fixed to an end of the cam shaft 120 extending through the printer housing 2 the elongated lever 50 has one end 124 fixed to the cam shaft 120 and is pivotable about the cam shaft axis 113 shown in fig1 and 12 between a lock position shown in fig1 and an unlock position shown in fig1 pivoting the lever 50 about the cam shaft axis 113 between the lock and unlock positions rotates the camshaft 120 to engage and disengage the cam 118 from the pivot linkage 104 advantageously in the lock position the lever opposed end 127 extends over the receptacle 18 and engages the top wall shelf 48 of the cartridge 12 to lock the cartridge 12 in the receptacle 18 in the unlock position the lever 50 is disengaged from the cartridge 12 and allows the cartridge 12 into or out of the receptacle preferably the lever 50 includes a rib 122 extending along a lever edge to.