A motor-operated cylinder

Abstract: A motor-operated cylinder is provided, wherein the rotational movement of the output shaft of a motor is converted into a linear movement by a thread mechanism 3, with the least possible load applied to the thread mechanism 3 when an object starts to be moved. The motor-operated cylinder is equipped with a booster 14 so that propelling forces exerted by both the thread mechanism 3 and booster 14 simultaneously act on a retractable rod 6.

Description: Field of the Invention This invention relates to improvements of a motor-operated cylinder wherein the rotational movement of the output shaft of a motor is converted into a linear movement by a thread mechanism. Background of the Invention In a case where, for example, an object on a roller conveyor is moved by being pushed with the conventional so-called motor-operated cylinder, the weight of the object, the resistance caused by the static friction of ball bearings acting on the rollers, and a load (reaction) to accelerate the object to a given speed, are applied simultaneously to the front end of the retractable rod of the cylinder when the object starts to be moved. Since the resistance caused by the static friction of the ball bearings acting on the rollers when the movement of the object starts is far greater than that caused by the dynamic friction of the ball bearings acting on the rollers during the movement of the object, a significant load is applied to the retractable rod of the motor-operated cylinder when the object starts moving. As a result, there is a problem in that the threaded part of the thread mechanism quickly wears away, so that in general the life of the motor-operated cylinder shortens. From EP 0 163 602 A2, a motor-operated linear drive means in accordance with the preamble of appended claim 1 is known. This invention was made considering the above circumstances. Its purpose is to provide an improved motor-operated cylinder, wherein only the least possible load is applied to the thread mechanism thereof when an object to be moved starts moving. Summary of the Invention To achieve the above object the motor-operated cylinder of this invention is constituted such that a booster comprising the characterizing features of claim 1 is added to the retractable rod so as to have propelling forces exerted by both the thread mechanism and the booster act simultaneously on the retractable rod. Brief Description of the Drawings Fig. 1 is a partially sectional elevation showing a first embodiment of this invention. Detailed Description of the Invention A first embodiment of this invention will now be described by reference to Fig. 1. As shown in the drawing, a ball-bearing block 2 is fixed in a cylindrical body 1, extending in a horizontal direction, at its right side (as viewed from the front). One end part (the right side) of a threaded shaft 4 of a ball-thread mechanism 3 is fitted in the ball-bearing block 2. One end part (the right side) of a hollow retractable rod 6, which holds the threaded shaft 4, and which extends coaxially within the cylindrical body 1, is fixed to a nut 5, which has built-in balls of the ball-thread mechanism 3. The other end part (the left side) of the retractable rod 6 slidably passes through a lid 7 fixed to the left end of the cylindrical body 1. A casing 8 is mounted on the right end of the cylindrical body 1. A horizontal motor 9 is mounted on the left outer side of the casing 8. The output shaft of the motor 9 and the right end of the threaded shaft 4 are connected by a transmission mechanism 10 consisting of a belt and a belt pulley. A rail member 11, extending along, and in the same direction as, the cylindrical body 1, is mounted on its inner side. A slider 12, which prevents the retractable rod 6 from rotating by slidably engaging the rail member 11, is fixed to the right end of the retractable rod 6. The slider 12 has on its upper surface a projection member 13. A cylinder mechanism 15, which constitutes a part of the booster 14, is mounted on the upper surface of the ball-bearing block 2. This cylinder mechanism 15 is structured such that when the retractable rod 6 has contracted a certain distance after a cylindrical body 16 of the cylinder mechanism 15 has expanded in the same direction as that of the rod 6, the front end of its output rod 16a starts to abut the projection member 13. A check valve 17, a throttle valve 18, a closing valve 19, and an accumulator 20 with a built-in pressurized gas, all of which are communicatively connected in that order to constitute the remaining part of the booster 14, are disposed on the opposite side of the output rod 16a. The operation of the thus-constituted motor-operated cylinder when it is applied to an object on a roller conveyor (not shown) will now be explained. As is clear from the drawing, the retractive rod 6 is contracted by the reverse drive of the motor 9, and the output rod 16a of the cylinder mechanism 15 of the booster 14 is pushed into the cylindrical body 16 to be contracted. Thus a part of the pressure oil in the body 16 is returned into the accummulator 20 by being passed through the check valve 17, throttle valve 18, and closing valve 19, in that order, to be pressurized therein. To move the object under this condition, i.e., when the closing valve 19 and check valve 17 are opened while the motor 9 is started, the rotational force of the output shaft of the motor 9 is transmitted via the transmission mechanism 10 to the threaded shaft 4 of the ball-thread mechanism 3 so that the shaft 4 starts to rotate. The nut 5 of the ball-thread mechanism 3 starts to move toward the left while being prevented from rotating by the slider 12 and rail member 11, and at the same time as this the output rod 16a of the booster 14 is pushed toward the left by the oil pressure of the accummulator 20. As a result, the retractable rod 6 is expanded by a propelling force exerted by the projection member 13, which is thus forcedly pressed toward the left by the booster 14, besides being forcedly pressed by the original driving force exerted by the ball-thread mechanism 3. Although in the above embodiment the booster 14 is provided only on the side where the rod contracts, effects similar to this can be obtained when it is provided on the other side, namely, the expansion side. As is clear from the above explanation, in this invention a booster is added to the retractable rod such that propelling forces exerted by both the thread mechanism and booster simultaneously act on the retractable rod. Hence, the apparatus of this invention has great effects in that a load acting on the thread mechanism at its start can be kept as low as possible so that its life is greatly prolonged over that of the conventional one.

Claims: A motor-operated cylinder for converting via a thread mechanism (3) the rotational movement of the output shaft of a motor (9) into a linear movement, comprising a cylindrical body (1), and a hollow retractable rod (6), which is coaxially disposed in the cylindrical body (1), and which is propelled and reciprocated by the thread mechanism (3) so that the rod (6) is retractable relative to the cylindrical body (1), and a booster (14) disposed in the cylindrical body (1) for propelling the expansion or contraction movement of the retractable rod (6) when the rod (6) starts expanding or contracting from its contracted or expanded state, characterized in that the booster (14) comprises a cylinder mechanism (15), having a cylindrical body (16) and an output rod (16a), for propelling the expansion or contraction movement of the retractable rod (6) while the output rod (16a) is engaged with the retractable rod (6), and an oil-pressure mechanism, having a check valve (17), a throttle valve (18), a closing valve (19), and an accumulator (20) with a built-in pressurized gas, for forcedly pushing or drawing the output rod (16a) so as to propel the movement of the retractable rod (6). A motor-operated cylinder of claim 1, wherein the booster (14) is disposed at a position near the end part of the retractable rod (6) where the rod is in its most contracted position. A motor-operated cylinder of claim 1, wherein the booster (14) is disposed at a position near the end part of the retractable rod (6) where the rod is in its most expanded position.

Inventors: KIMURA KUNIMASA, MURATA ISAO, TOYODA SHIGEHIRO, KIMURA, KUNIMASA, MURATA, ISAO, TOYODA, SHIGEHIRO
Applicants: SINTOKOGIO LTD, SINTOKOGIO, LTD.
Application year: 1997
Main classification: B65G47
IPC codes: F16H25, B65G25, H02K7