Ball screw device and injection molding machine incorporating the same

A ball screw device of a plurality of rows, in which a plurality of ball screw shafts whose thrust direction is restrained by a fixed member are provided in parallel, said ball screw shafts are rotated synchronously to be subjected to an even load, and a working body connected to a ball screw nut engaging threadedly with said ball screw shaft is moved linearly, wherein

• said ball screw device comprises a plurality of ball screw nuts which engage threadedly with each of said ball screw shafts;
• a sensor carrying flange which attaches one of all of said ball screw nuts to a working body;
• a load sensor which is mounted on said sensor carrying flange;
• an attachment flange which directly attaches said working body to one of said ball screw nuts on the ball screw shaft other than the ball screw shaft with which the ball screw nut having said load sensor engages;
• an annular fluid pressure piston which is attached to the ball screw nut other than said one ball screw nut;
• a plurality of fluid pressure cylinders, each of which is attached to said working body and has an annular groove portion in which said piston fits in a fluid-tight manner to form a fluid pressure actuator;
• a fluid pressure control unit which controls each fluid pressure of each of said cylinders so as to produce a piston pushing force equal to the detected load of said load sensor;
• and a pipe which transmits the fluid pressure controlled by said fluid pressure control unit to said fluid pressure cylinders, so that a load is applied to said working body, the load is distributed evenly to said ball screw nuts.

A ball screw device which converts the rotation of a ball screw shaft whose thrust direction is restrained by a fixed member into linear movement of a ball screw nut engaging threadedly with said ball screw shaft to move a working body connected to said ball screw nut, wherein

• said ball screw device comprises a plurality of ball screw nuts which engage threadedly with said ball screw shaft;
• a load sensor which is installed on said working body or said fixed member to detect a load on said working body;
• an attachment flange which directly connects one of said ball screw nuts to said working body;
• an annular fluid pressure piston attached to the ball screw nut other than the ball screw nut connected to said attachment flange;
• a plurality of fluid pressure cylinders, each of which is attached to said working body and has an annular groove portion in which said piston fits in a fluid-tight manner to form a fluid pressure actuator;
• and a fluid pressure control unit which controls the fluid pressure of each of said fluid pressure cylinders so as to produce a piston pushing force equal to a value obtained by dividing the load detected by the load sensor of said working body by the number of ball screw nuts, so that a load is applied to said working body, the load is distributed evenly to said ball screw nuts.

A ball screw device of a plurality of rows, in which a plurality of ball screw shafts whose thrust direction is restrained by a fixed member are provided in parallel, said ball screw shafts are rotated synchronously to be subjected to an even load, and a working body connected to a ball screw nut engaging threadedly with said ball screw shaft is moved linearly, wherein

• said ball screw device comprises a plurality of ball screw nuts which engage threadedly with each of said ball screw shafts;
• a load sensor which is installed on said working body or said fixed member to detect a load on said working body;
• an attachment flange which directly connects one of said ball screw nuts located on the same shaft of each of said ball screw shafts to said working body;
• an annular fluid pressure piston attached to the ball screw nut other than the ball screw nut connected to said attachment flange;
• a plurality of fluid pressure cylinders, each of which is attached to said working body and has an annular groove portion in which said piston fits in a fluid-tight manner to form a fluid pressure actuator;
• and a fluid pressure control unit which controls the fluid pressure of each of said fluid pressure cylinders so as to produce a piston pushing force equal to a value obtained by dividing the load detected by the load sensor of said working body by the total number of ball screw nuts, so that a load is applied to said working body, the load is distributed evenly to said ball screw nuts.

A ball screw device which converts the rotation of a ball screw shaft whose thrust direction is restrained by a fixed member into linear movement of a ball screw nut engaging threadedly with said ball screw shaft, and has a load configuration such that the load for moving a working body connected to said ball screw nut in the direction of one side is considerably larger than the load for moving said working body in the opposite direction, wherein

• said ball screw device comprises a first ball screw nut provided on said working body so that an attachment flange is located on the side opposite to the heavy load direction of said ball screw shaft;
• an oil pressure cylinder fixedly provided on said working body;
• an oil pressure piston which is fitted in said oil pressure cylinder in a fluid-tight manner and is attached to said first ball screw nut;
• an oil pressure source which applies a predetermined oil pressure to a ring-shaped oil pressure chamber formed by said oil pressure piston and said oil pressure cylinder;
• and a second ball screw nut installed fixedly to said working body so that said attachment flange is located on the side opposite to the heavy load direction of said ball screw shaft, and said ring-shaped oil pressure chamber is filled with a working fluid of a predetermined pressure and holds it, and a pre-load of a predetermined percentage of the maximum load is always applied to said working body, so that at the time of the maximum load, said two ball screw nuts share the maximum load of said ball screw shaft.

A ball screw device which converts the rotation of a ball screw shaft whose thrust direction is restrained by a fixed member into linear movement of a ball screw nut engaging threadedly with said ball screw shaft, and has a load configuration such that the load for moving a working body connected to said ball screw nut in the one-side direction is considerably larger than the load for moving said working body in the opposite direction, wherein

• said ball screw device comprises a first ball screw nut provided on the front side of said working body so that an attachment flange is located on the side opposite to the heavy load direction of said ball screw shaft;
• an oil pressure cylinder fixedly provided on said working body;
• an oil pressure piston which is fitted in said oil pressure cylinder in a fluid-tight manner and is attached to said first ball screw nut;
• an oil pressure source which applies a predetermined oil pressure to a ring-shaped oil pressure chamber formed by said oil pressure piston and said oil pressure cylinder;
• and a second ball screw nut installed fixedly to the rear side of said working body so that said attachment flange is located on the side opposite to the heavy load direction of said ball screw shaft, and said ring-shaped oil pressure chamber is filled with a working fluid of a predetermined pressure and holds it, and a pre-load of 40 to 50% of the maximum load is always applied to said working body, so that at the time of the maximum load, said two ball screw nuts share the maximum load of said ball screw shaft.