Screw driving machine with contact arm locking mechanism

Abstract: A screw driving machine in which a screw having a head is screwed into a work, includes: a body; a nose section positioned toward the work with respect to the body, the nose section holding the screw to be driven; a hammering mechanism accommodated in the body, for hammering the screw into the work until the head of the screw held above the work; a screwing mechanism for screwing the screw hammered into the work; a contact arm slidable with respect to the nose section, the contact arm being pulled in toward the body when the contact arm is pushed against the work; and a locking mechanism for prohibiting the contact arm from sliding in its half way when the contact arm is pushed against the work, and for releasing the contact arm from locking after the hammering mechanism hammers the screw into the work.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a screw driving machine which hammers a screw and then screws it. More particularly, the invention relates to a contact arm locking mechanism in a screw driving machine in which a contact arm is locked by a locking mechanism on its half way. 2. Related Art A screw driving machine, as disclosed by GB-A-2 271 532 has a driver which performs a screw hammering operation in a direction of axis, and a screwing operation around axis. The driver is driven by compressed air to hammer a screw into a material into which a screw is to be screwed (hereinafter referred to merely as "a work", when applicable), and screw the screw into the work. If, in the screw hammering operation, the stem of the screw penetrates the work, then the following screw screwing operation means nothing, and the screw has little extracting resistance from the work. Thus, in order to sufficiently hold the screw screwed in the work, it is essential to hammer the screw into the work to a predetermined depth according to the thickness of the work. Hence, heretofore, as shown in the aforementioned document, in order to make the screw hammering stroke of the driver to end at a predetermined position, the following hammering depth control mechanism is employed: A contact member which abuts against the work is arranged slidably along a nose section from which screws are ejected. In hammering a screw into the work, the contact member is held at a predetermined stop position to hold the nose section at a predetermined distance (or at a predetermined height) from the surface of the work, thereby to adjust the screw hammering depth. In the above-described hammering depth control mechanism, a rotary arm integral with the rotary shaft of a pinion-rack mechanism is engaged with the upper end of the contact member. When the trigger lever is operated, the screw hammering operation is started. Thereafter, the pinion-rack mechanism is operated. In association of the operation of the rack, the rotary arm is rotated to release the contact member, so that the screw screwing operation is carried out. Since, the screwing mechanism starts before the contact arm is released, difficulties may arise. The upper end of the contact member is then moved to a retracting position located above beyond the position of the rotary arm. When the trigger lever is released after the screw screwing operation, the rack is returned to its initial position, and the rotary arm is rotated to the initial position. Further, the rotary arm, while rotating to the initial position, may strike against the side surface of the contact member, thus obstructing the returning of the contact member. If the contact member is not returned to the initial position, in the next screw hammering operation, it is impossible to hammer the screw to the predetermined depth, and the pinion gear coaxial with the rotary arm cannot be returned to the initial position. Hence, in the next screw screwing operation, the screw is not sufficiently rotated, so that the screw is not sufficiently held in the work. SUMMARY OF THE INVENTION An object of the invention is to eliminate the above-described difficulties accompanying a conventional screw driving machine. More particularly, an object of the invention is to provide a hammering depth control mechanism for a screw driving machine in which, even when the trigger lever is released with the contact member retracted along the nose section, the contact member can be returned to the initial position, and the pinion gear is also positively returned to the predetermined position. The main object of this invention is, however, to provide a bit disengagement preventing mechanism for a screw driving machine which prevents the bit from disengaging from the driving groove formed in the head of a screw after the screw has been hammered into an work to a predetermined depth. According to the invention, there is provided a screw driving machine as defined in claim 1. Preferred embodiments are defined in the dependent claims. The screw driving machine thus constructed functions as follows: In hammering a screw into the work, the end of the contact member is pushed against the surface of the work, so that the contact member is slid along the nose section. When, under this condition, the hammering mechanism is operated, the screw is hammered into the work. In this operation, the locking piece is at the first position. There-fore, while the contact member is retracted along the nose section, the locking piece is engaged with the engaging step, to regulate the amount of retraction. On the other hand, the end of the contact member is protruded from the end of the nose section. Hence, when the driver of the hammering mechanism is moved a predetermined distance, the screw hammering depth is decreased as much as the amount of protrusion of the contact member from the nose section. Thus, the screw hammering depth is controlled. After the screw hammering operation is finished the locking mechanism, is operated to release the contact member. As a result, the locking piece is retracted from above the engaging step, and the contact member is retracted again. Thus, the screw can be screwed into the work. That is, the pinion-rack mechanism rotates the driver, thereby to screw the screw into the work. After the screw screwing operation, the rack of the pinion-rack mechanism is returned to the initial position, while the pinion gear is also rotated to the initial position. If, in this case, the contact member has been returned to the initial protruded position, the locking piece is also returned to the first position. In the case where the contract member is held retracted, the locking piece strikes against the contact member. However, the locking piece is held where it has struck against the contact member, and is rotated to the first position for instance by the elastic force of a spring when the contact member is returned to the initial protruded position. As is apparent from the above description, even if the trigger lever is released when the contact member is retracted along the nose member, the contact member can be returned to the initial position, and the pinion gear is also positively returned to the predetermined position. Hence, the screw driving machine of the invention is substantially free from the difficulties that the contact member returning operation is obstructed, so that when the next screw is not hammered to the predetermined depth, or it is not sufficiently screwed into the work, with the result that the screw is not sufficiently held in the work. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional diagram showing the arrangement of the screw driving machine according to the invention; FIG. 2 is an explanatory diagram for a description of the hammering operation of the screw driving machine; FIG. 3(a) and 3(b) are explanatory diagrams for a description of the operation of a locking mechanism; and FIG. 4 is a perspective view showing essential components of the locking mechanism. FIG. 1 shows a screw driving machine according to the invention. The machine comprises: a hammering mechanism a ; and a screwing mechanism b . The hammering mechanism a is designed as follows: A hammering piston 104 with a screw driving bit 103 is vertically slidably provided inside a hammering cylinder 102 in a machine body 101. Compressed air is supplied into the hammering cylinder 102 to drive the hammering piston 104, thereby to cause the bit 103 to strike the screw 106 (supplied in a nose section 105 provided at the end of the machine body 101) until the screw is hammered into the work to a predetermined depth, with its head held above the work. The screwing mechanism b is designed as follows: An air motor 107 is driven by part of the compressed air supplied to the hammering cylinder 102, to screw the screw 106 into the work which has been hammered. The compressed air is supplied to the hammering cylinder 102 from a compressed air supplying source through an air chamber 109 which is formed in a grip 108 and the machine body 101. Screws 106 to be driven are arranged one after another on a belt-shaped coupling material, and are accommodated in a magazine 110 with the belt-shaped coupling material coiled. The screws 106 are supplied to the nose section 105 one at a time by an air cylinder device 111 for supplying the screw. The hammering mechanism a is operated by operating a trigger lever 112. When the trigger lever 112 is operated, a trigger valve 113 is operated. In association with the operation of the trigger valve 113, a head valve 114 is opened as shown in FIG. 2, so that the compressed air is abruptly supplied from the air chamber 109 to the hammering cylinder 102 to drive the hammering piston 104. The screw 106, when hammered by the hammering mechanism a , is partially pushed into the work. The screw 106 thus pushed is screwed into the work with the screwing mechanism b . When, on the other hand, the trigger lever 112 is released, the trigger valve 113 operates to cause the head valve 114 to close the hammering cylinder 102 from the air chamber 109, and opens it to an discharge opening. As a result, the pressure applied to the upper surface of the hammering piston 104 is decreased, while the pressure applied to the lower surface is increased by the compress air which has been stored in a blow-back chamber 116 while being compressed by the hammering piston 104 during the hammering operation. That is, the pressure applied to the lower surface of the hammering piston 104 becomes higher than that applied to the upper surface, and therefore the latter 104 is returned to the uppermost point. The screwing mechanism b is to transmit the rotation of the output shaft 117 of an air motor 107 through an intermediately gear 118 to a drive gear 119, thereby to rotate the bit 103 which is inserted into a non-circular through-hole formed in the drive gear 119 at the center. The air motor 107 is coupled through an air passageway 120 to the hammering cylinder 102, so that the former 107 is rotated by the compressed air supplied into the hammering cylinder 102. The air passageway 120 is communicated through the hammering cylinder 102 and through a passageway 120a with the air inlet section 120b of the air motor 107. Hence, after the operation of the hammering mechanism a , the screwing mechanism b is operated by the compressed air supplied through the air passageway 120, to screw the screw 106 into the work 115 which has been hammered. The bit 103 is so arranged that it is slidable along the axis of the drive gear 119 and is tunable together with the latter 119. The air cylinder device 111 is shown in FIGS. 1 and 3. That is, a feed piston 123 is slidably set in a cylinder 122. A feed pawl 126 is swingably coupled to a supporting pin 125 connected to the end of a feed rod 124 which is coupled to the feed piston 123. The feed piston 123 is kept urged by a spring 127 towards a screw feed side. Compressed air is supplied through an air supply hole 128 formed in the cylinder 122, to move the feed piston backwardly a predetermined distance corresponding to one screw. The air supply hole 128 is communicated through an air passageway (not shown) with the blow-back chamber 116. When the screw is hammered, the compressed air is supplied from the blow-back chamber 116 to the cylinder 122 to move the feed pawl 126 backwardly. After the screw has been hammered, the compressed air is discharged from the blow-back chamber 116, while the compressed air is discharged from the cylinder 122. Hence, the feed piston 123 is operated in the screw feed direction, so that a screw is fed into the nose section 105. Therefore, the feed piston 123 is normally positioned by the spring 127 at the end on the screw feed side. In FIG. 1, reference numeral 121 designates a contact arm. The contact arm 121 is slidable along the nose section 105. More specifically, as the end of the contact arm 121 is pushed against the work 115, the contact arm 121 is pushed back towards the machine body (or relatively moved upwardly). As a result, the upper end of the contact arm 121 is moved upwardly, to make the pull-in operation of the trigger lever 112 effective (in operating the trigger valve 113). That is, it has the same safety device as an ordinary nailing machine. The lower end portion of the contact arm 121 is formed cylindrical so as to surround the nose section 105. The contact arm 121 functions as safety means as was described above. In addition, the contact arm 121 prevents the screw from being hammered entirely into the work 115. That is, the contact arm 121 functions to stop the end of the bit 103 above the surface of the work 115; that is, the screw is hammered with the head of the screw away from the surface of the work. Hence, the contact arm 121 is so designed that it is moved (slid) in two steps. For this purpose, the contact arm 121 has a locking mechanism c so that, in the first step, the safety means is released, and the screw is hammered into the work with its head held above the work (cf. FIG. 2). More specifically, in the first step, the contact arm 121 thus moved is locked by the locking mechanism. After the screw is hammered to the predetermined depth, the locking mechanism is released, so that the contact arm 121 is allowed to perform its second movement. Thus, the screw is screwed into the material. The above-described locking mechanism c , as shown in FIG. 3(a) and FIG. 4, comprises: a locking piece 130 which operates in association with the air cylinder device 111. The locking piece 130 is moved into or out of engagement with the cylindrical portion 131 of the contact arm 121. The locking piece 130 is swingably mounted on the supporting pin 125 of the feed rod 124 of the air cylinder device 111, and urged by a spring 132 in one direction. The feed piston 123 is normally positioned by the spring 132 at the end on the feed side. The end of the locking piece 130 is so shaped that, under this condition, it is engaged with the upper edge 131a of the cylindrical portion 131 when the contact arm 121 is moved upwardly, and the movement of the contact arm 121 is locked in the first step. When the feed piston 123 is moved in the feed direction, the end of the locking piece 130 is caused to strike the arm portion of the contact arm; however, in this case, the locking piece 130 is pivoted about the supporting pin 125 against the elastic force of the spring 132; that is, it moves sideward (in the direction of the arrow A in FIG. 4, thus not obstructing the movement of the feed pawl 126. When, on the other hand, the hammering mechanism a is activated in response to the "on" signals from the trigger valve 113 and the head valve 114, the compressed air is supplied from the block-back chamber 116 into the cylinder 122 of the screw feeding air cylinder device 111, so that the locking piece 130 together with the feed pawl 126 is moved backwardly, thus disengaging from the contact arm 121; that is, the locking mechanism c is released. In hammering the screw 106 of the screw driving machine thus constructed, the lower end of the contact arm 121 is pushed against the work 115 as shown in FIG. 2, the contact arm 121 is slid upwardly (towards the machine body 101) to the first step position (indicated by the dotted lines in FIG. 4) where it is locked by the locking mechanism c . This slide operation makes the trigger lever pulling operation effective. Hence, by drawing the trigger lever 112, the hammering mechanism a is operated; that is, the hammering piston 104 is driven, so that the screw is hammered to a predetermined depth with its head held above the work. In driving the hammering piston 104, the air in the blow-back chamber 116 is compressed, and the air thus compressed is supplied into the screw feeding air cylinder device 111 as shown in FIG. 4, so that the feed piston 123 is moved backwardly against the elastic force of a spring 127. Hence, the locking piece 130 is also moved backwardly, thus disengaging from the upper edge 131a of the cylindrical portion 131 of the contact arm 121. In the hammering operation, part of the compressed air supplied to the hammering cylinder 102 is applied to the air motor 107 to drive the screwing mechanism b . As a result, the bit 103 is rotated; that is, it is rotated while engaging with the driving groove in the head of the screw 106, so that the latter 106 is screwed into the work 115. The locking mechanism c is released by the compressed air in the blow-back chamber 116, whereas the screwing mechanism b is operated by the compressed air in the hammering cylinder 102. The releasing of the locking mechanism c is achieved earlier than the screwing. When, after the screw has been screwed into the material 115, the trigger lever 112 is released, the hammering piston 104 is returned to its initial position, while the compressed air is discharged from the blow-back chamber. Hence, the feed piston 123 of the air cylinder device 111 feeds another screw with the aid of the spring 127 as shown in FIG. 4, and the locking piece 130 of the locking mechanism c is moved to engage with the contact arm 121. With the above-described screw driving machine, the screw 106 is hammered and screwed through the following operating steps: operating the locking mechanism c , releasing the safety means, hammering the screw with the hammering mechanism, releasing the locking mechanism c , and screwing the screw with the screwing mechanism. That is, after the screw 106 is hammered to the predetermined depth, with the locking mechanism c of the contact arm 123 released, the bit 103 is engaged with the head groove of the screw 106 and then rotated. This feature effectively prevents the bit from disengaging from the screw which is to be screwed in. The invention is not limited to the above-described embodiment. For instance, the locking mechanism c may be so designed as to lock the contact arm in the first step. In addition, the above-described screw feeding air cylinder device may be replaced with an air cylinder different from it. In the above-described embodiment, the signal for releasing the locking mechanism is of the compressed air in the blow-back chamber 116; however the invention is not limited thereto or thereby. For instance, an independent source of compressed air may be employed.

Claims: A screw driving machine for driving a screw (106) having a head into a workpiece (115), comprising: a body (101); a nose section (105) attached to the body (101) so as to be, in use, more proximal to the workpiece (115) than the body (101), the nose section (105) being capable of holding the screw (106) to be driven; a hammering mechanism (a) accomodated in the body (101) and having a bit (103) for hammering the screw (106) into the workpiece (115) until the head of the screw (106) is held above the workpiece (115); a screwing mechanism (b) for turning the bit (103), thus screwing the screw (106) hammered into the workpiece (115); a contact arm (121) slidably supported on the nose section (105) so as to be capable of sliding in longitudinal direction of the screw (106), the contact arm (121) protruding beyond the nose section (105) toward the workpiece (115) and being capable of sliding, in use, relative to the nose section (105) when being pushed against the workpiece (115); and a locking mechanism (c) capable of preventing the contact arm (121) from sliding over its full trajectory, when the contact arm (121) is pushed against the workpiece (115), and to release the contact arm (121) from locking after the hammering mechanism (a) has finished hammering the screw (106) into the workpiece (34; 125); the locking mechanism (c) comprising: an upper edge (131a) formed on the contact arm (121); and a supported locking piece (130) being movable between a first position where the locking piece (130) engages with the upper edge (131a) when the contact arm (121) is pushed against the workpiece and a second position where the locking piece (130) does not interrupt sliding of the contact arm (121); characterised in that the screw driving machine is adapted so that the locking mechanism (c) releases the contact arm (121) from locking before the screwing mechanism (b) starts turning. The screw driving mechanism according to claim 1, wherein the screwing mechanism (b) includes an air motor (107). The screw driving machine according to claim 2, wherein the screw driving machine further comprises an air cylinder device (111) including: a cylinder (122); a feed piston (123) slidably set in the cylinder (122); and a feed pawl (126) pivotally connected to the feed piston (123), for feeding the screw (106) to be hammered, the feed pawl (126) pivotally supporting the locking piece (130) of the locking mechanism (c). The screw driving machine according to one of claims 1 to 3, characterised in that a screw (106) is fed into the nose section (105) by an air cylinder device (111) and that the locking piece (130) is supported by the air cylinder (127), wherein the air cylinder device (111) normally keeps the locking piece (130) to the first position and moves the locking piece (130) to the second position at the same time that the compressed air for hammering a screwing bit (103) is discharged.

Inventors: FUKUSHIMA YOSHIO, TAKEZAKI MITSUGU, FUKUSHIMA, YOSHIO, TAKEZAKI, MITSUGU
Applicants: MAX CO LTD, MAX CO., LTD.
Application year: 1996
Main classification: B25B21
IPC codes: B25B21