WO1995030554A1 - Machine for tensioning and nailing a canvas on an artists' frame - Google Patents

Abstract

A machine for tensioning and nailing a canvas on an artists' frame comprising four sidewalls (3, 4, 5, 6) defining a working station (7) with canvas stretching tongues (12) having a high coefficient of friction on the upper canvas supporting face and a low coefficient of friction on the opposite lower face. The nailing step is accomplished by means of nailing units (14) which receive the nails (17) from to and fro sliders (48) movable on said sidewalls and which, in turn, receive the nails (17) from vibrating nail feeders (49) during the return of said sliders (48) by means of nail drawing and synchronism units (105). The canvas (10) and superimposed frame (11) can be lowered from a supporting plane in the working station (7) into a nailing plane by means of a number of lever-like swivellable pressing arms (119) which are removably fixed to a respective driving shaft (115) supported on a respective sidewall (3, 4, 5, 6).

Description

Machine for tensioning and nailing a canvas on an artists' frame

The present invention relates to a machine for tensioning and nailing a canvas on an artists' frame having the features pointed out in the preamble of claim 1.

A machine of this kind, according to the preamble of claim 1, is known from the Italian patent No. 1 129 619.

The machines disclosed by said patent as well as similar machines which has been commercialized bevore the filing date of said patent, have the advantage to performe the working cycle consisting of two consecutive steps concerning the application of the canvas on the frame and the nailing of said canvas on the frame, simultaneously on all four sides of the latter. The complete working cycle also includes a preliminary folding step for folding the canvas corners onto the frame . corners and a final ejection step for ejecting the frame after the nailing . step.

The foundamental features of these machines are inferable from the enclosed figures 1 to 6 showing the prior art and are illustrated in the following.

On a frame 1 of a machine 2 are supported four sidewalls 3, 4, 5 and 6 defining a working station 7. In the case of fixed sidewalls it will be possible to nail wooden frames of only one size whereas with a machine having movable, that is adjustable sidewalls it will be possible to nail wooden frames of different sizes comprised between a smallest size and a largest one defined by the maximun approach of said sidewalls to each other and the maximun spacing away of the latter, respectively. In the case of movable sidewalls for example the sidewall 3 is stationary 2 whereas the sidewalls 4, 5, and 6 are movable according to the arrows fl to f4.

The displacement of said movable sidewalls takes place from an hydraulic cylinder-piston unit 8 by means of a group 9 of gear wheels, transmission wheels and linking arms connected to said movable sidewalls. In the working station 7 is provided a number of flexible supporting and folding tongues 12 for supporting and applying a canvas 10 onto a frame 11. Said tongues are fixed at one end thereof to a sidewall, project toward the interior of the working station and at their facing free ends are connected to each other by means of cord-like elastics 13, thereby forming a chess-board-like supporting plane for supporting a canvas and a superimposed frame.

Each sidewall lodges a plurality of horizontal nailing units in the form of pneumatic or mechanical operated cylinder-piston or rack-pinion units 14 comprising each a nailing rod 15.

Each nailing rod 15 lodges at its free end a magnet 16 for supporting and positioning a nail 17, whereby said free ends of said nailing rods are horizontally movable in nailing bores 18 provided in each sidewall and opening into said working station 17 between two adiacent supporting tongues, respectively, and below the latter, that is in a nailing plane. Above in each nailing bore enters a throughgoing chamber 19 receiving a nail 17. In the applying step of said canvas 10 and during the manual feeding of said nails 17 the receiving chambers are closed below by a nailing rod 15, respectively.

Since the surface of the canvas 10 is greater than the surface of the respective frame 11, and at the frame corners the canvas is to be folded on itself at each corner of the working station 7 is provided a pivotably mounted element 20 for supporting and preliminary folding the canvas at the frame corners prior to the canvas applying step. The nail feeding is carried out manually by means of a ruler-like nail loader which is guided by an operator onto the upper edge 22 of a L- shaped section 23 fixed with its horizontal side 24 to the top surface of a respective sidewall. In said horizontal side are provided throughgoing bores 25 coincident with the underlying receiving chambers 19. On the contrary, in the vertical side 26 are provided throughgoing apertures 27 into which opens a respective slot 28 which is open toward the upper edge 22.

The nails 17 fall consequently from a slot 28 into a respective throughgoing chamber 27, from the latter each nail slides into the respective bore 25 and falls with its head downwards into a receiving chamber 19 and then, after the backward stroke of the respective nailing rod 15, the nail falls into the respective nailing bore 18 where it is attracted and positioned horizontally by means of the magnet 16 which supports the nail by the head thereof. During the following forward stroke of the nailing rods takes place the nailing step of the canvas onto the frame, after the preliminary folding of the canvas around the frame sides and the canvas applying step as well as the lowering of the frame in the nailing plane.

For the application of the canvas 10 around the frame the latter is lowered from a supporting position A on the supporting tongues 12 into the underlying nailing position B by means of a hood-shaped pressing frame 30 which is vertically movable above the working station 7. During the lowering of the wooden frame the supporting tongues are bent downwards and pushed backwards against the respective sidewall. The friction between the canvas and the tongues causes a folding of said canvas along the outer faces of the frame with an unpretentious tensioning of the canvas on the frame. After the nailing step cylinder- piston unite which are vertically fixed to the sidewalls below the nailing plane cause the frame ejection.

The frames which can be nailed in these machines are of the expandable type, that is they include expansion springs lodged in plastics angular supports 31 housing the side ends of the frame sides.

Said springs are inserted into said angular supports after the nailing of the frame and tend to space away the frame sides form each other and effect, therefore, the real tensioning of the canvas, whereby said tensioning is, however, modest.

The machines belonging to the prior art have heavy limits and drawbacks.

After the nailing process the frame is clamped between the sidewalls in the working station and the supporting tongues which are composed of a portion of a rubber ribbon are pressed between the frame and said sidewalls. The frame ejection has to overcome a very heavy friction between the front face of said supporting tongues and the canvas, on one side, and between the ear tongue face and the sidewalls, on the other side. This is possible because a strong ejection force is applied.

During the ejection step the ejction forces tend to tear-up the canvas from the frame and cause canvas deformations and tears. The known machines are not adapted to nail non-expandable frames, that is rigid frames having no springs.

The known supporting tongues are subjected to weare, in particular the ones lying in the corner zones of the working station and which are, therefore, always used with all frame sizes. This leads to an irregular tensioning of the canvas.

The manually nail insertion is slow and remarkably increases the working cycle time. Said working cycle time increases, moreover, as the frame dimensions become larger. In addition, is to consider the fact that the difficύltyes connected with the manually insertion of the nails, and with the hindrances due to the presense of said hood-shaped pressing frame usually require the presence of two operators. With two operators the daily production in 8 working hours is of about 900 frames, in the case of frames having small sizes (for example, in cm, 24 by 30 or 30 by 40) and of about 350 frames, in the case of frames having larger sizes (100 by 120 cm).

The hood-shaped pressing frame for lowering the canvas and the overlying frame from the supporting plane to the nailing plane is supported about 40 - 50 cm above the working station. Said hood- shaped frame remarkably limits the frame manipulation freedom, especially the handling of the larger wooden frames, and it also limits the mutual visibility of both operators, and also considerably increases the manufacturing costs of the machine. In addition, the hood-shaped frame hinder the application of feeding conveyors for the canvas sheets and the wooden frames as well as of evacuation conveyors for the nailed frames, whereby said conveyors are indispensable for a wholly automatic control of the machine.

The object of the present invention is to provide a machine of the described kind, with fixed or movable sidewalls, which permits to overcome the drawbacks of the known machines, to nail expandable as well as non-expandable frames with a strong tensioning of the canvas and without demaging the latter during the frame ejection step, to eliminate the hood-shaped pressing frame, and to provide drastically shortened working cycles.

In a machine with fixed or movable sidewalls having the features set forth in the preamble of claim 1, the above-mentioned object is reached with the features stated in the characterizing part of claim 1. Further deVeloppments and configurations are inferable from the characterizing part of the dependent claims.

With claim 2 are obtained two configurations of great stretching efficiency of the supporting tongues which permit a very good and lasting operation.

The springy pads pointed out in claim 3 can be easily manufactured and have a very efficient operation.

The nail transfering slider pointed out in claim 4 as weel as the driving means thereof can be producted easily and have small elongated dimensions which allow an easy housing of said slider and driving means in the respective sidewall.

The use, suggested in claim 5, of the sidewalls as stop elements co¬ operating with the nail transfering sliders is a solution which assures a reliable operation without requiring additional components. Claim 6 relates, to an embodiment assuring a reliable operation of the driving means of the nail transfer sliders as weel as of the latter. Claim 7 suggests a single and quick adaptation of the nails to be charged in the nail transfer sliders in function of the frame size. Claim 8 relates to a reliable configuration of a nail supplying device associated, at on end thereof, to a respective vibrating nail feeder and, at the other end, with a unit for charging the supplied nails into the nail transfer sliders.

Claim 9 suggests an expedient for an automatic reintroduction into the vibrating nail feeder of the nails having in the latter a wrong position for the supplying thereof.

Claim 10 suggests a simple and reliable configuration for a singularly drawing of the nails from a nail column and for distributing in synchronism said nails into a respective slider. The preloading positioning means suggested in claim 11 is simple and assures a reliable insertion of the supported nails into the slider nail receiving housings.

Claims 12 and 13 show advantageous configurations of the pressing arms which alllow the nailing of of frames having different widths of the frame sides.

The main advantage achivable with the the teaching of the present invention is to be seen mainly in a strongly increased machine productivity, which is achievable with the automatic nail feeding and with only one operator whose interventions advantageously require very short times and are decided by the operator himself. In other words, the working cycles can be strongly shortened.

In the machines having movable sidewalls the working cycles advantageously require the same time independently from the frame sizes.

In the case of very large frames it is advisable to involve two operators on opposite machine sides, what permits to exploit in the best manner the high machine productivity also with rather large frames, for example with frames having a size of 100 by 120 cm, with a hourly production of about 300 frames.

Another advantage is to be seen in the fact that the different coefficients of friction on both large faces or sides of the supporting tongues permit a strong canvas stretching also on non-expandable frames which latter are ejected in a smooth manner, what exludes whatever tensioning deformation or irregularity of the canvas stretching.

The abolition of the hood-shaped pressing frame improves the manipulation freedom in handling the frames above the working station and forms the indispensable prior condition for the adoption of automatic- devices for loading the canvas sheets and the frames and for the evacuation of the nailed frames.

A further advantage consists in the semplicity and rapidity of the machine adaptation to different frame sizes. Another advantage is to be seen in the reliable synchronism provided between the desplacement speed of the nail transfer sliders and the nail supplying speed of the nail drawingwheel or nail loader, what permits to further increase the stated productivity of about 300 frames/hour.

Further advantages will become apparent when reference is made to the following detailed description of the invention an the following drawings in which is diagrammatically shown a preferred embodyment of the machine according to the present invention.

In the drawings:

Figs. 1 to 6 illustrate views of the machine disclosed in IT-A- 1 129

619, and more specifically:

Fig. 1 is a middle cross section along the machine;

Fig. 2 illustrates a the topo view of a detail of the working machine;

Fig. 3 represents a sectional detail through a machine sidewall and the working station;

Figs. 4 and 5 represent two sectional details similarly to Fig. 3 with nailing parts in different positions;

Fig. 6 illustrates a detail of the sections for loading the nails;

Fig. 7 is a top view of a flat disposed canvas and a superimposed frame with angular supports as placed on the working station;

Fig. 8 is a perspective view of the frame of Fig. 7 with the canvas applied and nailed on the frame; and with reference to the machine according to the present invention: Fig. 9 illustrates a diagramatic top view in principle of a sidewall of the nailing machine, whereby the four sidewalls have in principle the same structure and comprise the same components;

Fig. 10 is an exploded view of a partially removed supporting tongue and a slipping leaf;

Fig. 11 is a side view of the assembled tongue of Fig. 10;

Fig. 12 represents the detail X in Fig. 11 in an enlarged scale;

Fig. 13 is a perspective view, partially brocken away, of a slidable slider for loading the nails;

Fig. 14 is a bottom view on the slider of Fig. 13;

Fig. 15 illustrates a perspective view of the front part of a slider;

Fig. 16 is an enlarged detail of the slider bottom side;

Fig. 17 is a side view of the front part of a slider;

Fig. 18 is an enlarged perspective view of the middle part of a sidewall in the zone of the nail feeder;

Fig. 19 is an enlarged perspective view of a detail of a sidewall without safety guard for the nailing units;

Fig. 20 is a perspective view of the sidewall part receiving the slider in the starting position;

Fig. 21 is a perspective view like Fig. 20, seen from above and with greater details;

Fig. 22 illustrates in a detail in perspective the pressing arms in the lowered position;

Fig. 23 represents in a front view and in a section a detail of the bill for the nail feeding with the nail separating and supplying wheel as well as the slider;

Fig. 24 is a side view partially in section of Fig. 23;

Fig. 25 is a front view of the syncronism star wheel; Fig. 26 illustrates an enlarged detail in the section along the plane XXVI-XXVI in Fig. 21;

Figs. 27 to 30 illustrate enlarged details of the different lowering positions of the canvas and the frame from the supporting plane to the nailing plane;

Figs. 31 to 33 represent details similar to those in Figs. 27 to 30, however during the ejection of a nailed frame; and Figs. 34 to 36 rerpresent enlarged details of the canvas and frame lowering step like Figs. 27 to 30, however in a second embodiment of the supporting and tensioning tongues.

With reference to Figs. 1 to 8, is first shortly depicted the operation of the known machines the foundamental structural features of which have been pointed out in the introductory part.

In Figs. 1 to 8 as well as in the remaining Figs. 9 to 36 equal components are designated with the same reference numerals. For . greater clarity of illustration the dimensional relationships in said figures are not always in scale.

For applying and nailing a canvas 10 onto a frame 11 said canvas is placed into the working station 7 by disposing the canvas onto the supporting plane made up of said supporting tongues 12 and said cord¬ like elastics 13. At the corners of the working station the canvas covers swivellable elements, not shown, for preliminary folding the canvas corners. Then an expandable frame 11 is superimposed on the canvas and it is positioned against appropriate, not shown, stop elements for centering purposes. The canvas and the frame are in the position A, Figs. 1 and 3. Then the pressing frame 30 is lowered and the wooden frame, with the underlying canvas, is lowered into the position B, Figs. 3 and 5. During this movement the projecting lateral canvas edges 32 slip along said supporting tongues 12 which are bent dawnwards and against the' respective sidewall, Fig. 3, whereas the nailing rods still close said throughgoing receiving chambers 19. At this time the nailing rods 15 are moved back, Fig. 4, the nails 17 fall into the nailing bores 18 and are positioned by the magnets 16, and subsequently takes place the feed movement of said nailing rods 15 so that the nails are driven into the canvas and the frame, Fig. 5.

Each of said nailing bores 18 opens obiously in the working station 7 between two adjacent supporting tongues 12. While the nailing rods move back shortly said hood-shaped frame 30 is lifted, Fig. 1, and not shown ejection elements in the working station eject upwards the nailed frame such that the operator can take away said nailed frame.

The supporting tongues 12 go back into the starting position A, whereby said tongues are assisted in their positioning by said cord-like elestics

13.

Prior to carry out a new working cycle the operator loads the nails 17_. into the receiving chambers 19 by sliding by hand a nail loader onto the sections 23 of the four saidwalls by walking personally around said sidewalls. The main drawbacks and disadvantages of the known machines have been illustrated in the introductory part.

The improvements according to the invention and mainly relating a strong tensioning of the canvas, and this also with non-expandable frames, an automatic nail feeding as well as the abolition of the overlying hood-shaped pressing frame, are now illustrated in details in the following description.

Due to the fact that the four sidewalls 3 to 6 have the same structure and the same components, the following description will be directed to only one sidewall wich is diagrammatically shown in a top view in fig. 9. As the machine structure or frame 1 can be designed at will, in the drawings will be omitted a detailed illustration thereof. In a first- 'embodiment the supporting tongues 12 according to the invention, Figs. 10, 11 and 12, are singularly made up of an upper friction tab 35 and by a lower separated slipping leaf 36 which is in facing relationship with said tab 35. As shown in Fig. 10, to the bottom of the tab 35 is strongly fixed, for example glued, a substantially non- stretchable weave 37 consisting for example of natural or chemical fibers which are mutually interconnected and bondeb by a per se known impregnation means. Alternatively, said weave or reinforcement structure may consists of a synthetic material sheet having a low coefficient of friction. The tab 35 consists of a material having a very high adhesion and resilience against the canvas sheets, for example linatex ®, rubber or other suitable material with a tickness between 1 to 6, preferably of 3 mm. The slipping leaf 36 consists of a synthetic material fabric or a sheet having a low coefficient of friction, for example nylon ® or kevlar ®. However the materials will be chosen such that between the tab 35 and the leaf 36 exists a very low coefficient of friction which permits a mutual slipping movement between said tab 35 and leaf 36 when pressed the one against the other. The tab 35 and the 36 are fixed together at one end thereof by means of a rivet 38 fixing a hook 39 for supporting said cord-like elastics 13. At the other ends said tabs and leaves are connected together by a screw 40, Figs. 27 and 31, which is inserted into the bores 41 and 42, Fig. 10, and secures said supporting tongue 12 to the respective sidewall 3 to 6. To each sidewall 3 to 6 on the vertical side 44 defining the working station 7 under each tongue 12 is fixed, for example glued, an elastic pad 45, Fig. 27, which in the shown embodiment is composed of foamed synthetic material.

At least one part of the front side 46 of said block-shaped pad 45 is sloping dawnwards and towards the interior of said working station 7 such as tσ define a wedge-like shape between two opposite sidewalls 3, 5 and 4, 6.

In each sidewall 3, 4, 5 and 6 the means provided for the transfer of the nails 17 into the nail receiving chambers 19 is designed for an automatic nail transfer and consists mainly of a nail transfer slider 48 which is longitudinally reciprocating movable on the sidewall and in vertical alignement with the througngoing receiving chambers 19 of the respective sidewall, with an associated vibrating feeder 49 of said nails 17 as well as with an interposed nail drawing and synchronism unit 105 described in more detail in the following.

Each slider 48 is for example slidable on his front part directly on a profiled guide section 50, fig. 19, which is covered by a safety guard 147, and on his rear part on a guiding rail 51, Figs. 21 and 26, by the interposition of a slide 52, whereby said guide 50 and said rail 51 are fixed to the top side 53 of the respective sidewall. Each slider 48 l as a reciprocating motion between a starting position C, outside the working station 7, and a nail discharging position D, inside said working station 7, and in which the nails 17 are discharged from the slider into said throughgoing receiving chambers 19 as illustrated in more details in the following.

Each slider 48 is made up of an upper strip 55 and by a lower diaphragm-like strip or diaphragm 56 which are both provided with a number of vertical throughgoing housings 57 and 58 respectively, corrisponding to the number of said vertical throughgoing receiving chamber 19 as well as to the number of said nailing units 14 of the respective sidewall and which all have the same nailing pitch P. The diaphragm 56 is longitudinally slidable supported in a limited way on the bottom side of the upper strip 55. The mounting take place by means of screws 59 screwed in said upper strip 55 and whose heads 60 are lodged' in the lowered rim 61 of throughgoing slots 62 of said diaphragm 56.

As is seen in particular in Figs. 13 and 14, between the stop element 64 fixed to the diaphragm 56 and the stop element 65, fixed to the strip 55 is lodged a preloading means, a spring 66 in the shown example, which causes an outgoing stroke F, Fig. 17, of the front end 67 of said diaphragm 56 from the upper strip 55 and a corresponding offset S between the nailing pitch P of the throughgoing housings 57 of the upper strip and the nailing pitch P of the throughgoing housings 58 of the diaphragm 56. The stroke F is defined by the impact between the screws 59 and the rear end 68 of the slots 62 in the feed direction of the slider 48.

The reciprocating control means of the slider 48 consists of a toothed transmission belt 70 which is turned round between two sprocket wheels 71 and 72. The sprocket wheel 72 is driven by e reversible motor 73, for example an electric one, preferably with the interposition of a clutch 74 having an adjustable maximun couple. The sections 76 and 77 of the belt 70 run beneath the slider 48 in its starting position and between said belt sections 76 and 77 is disposed said rail 51. The ends of said belt 70 are clamped between two jaws 78 forming a bracket 79 which is connected to the slide 52 and to the upper strip 55 of the slider 48. The connections are made, for example, by means of screws in a manner not shown in detail.

Each vibrating feeder 49 of the nails 17 is in principle of known type, is secured to to a respective sidewall at 47, Fig. 18, and comprises a container 81 having an internal helicoidal path 82 and an associated not shown vibrating unit.

In accordance with the invention next to the nail exit slot 83 in the wall of the container 81 is provided an opening 84 outside of which is formed a balcony-like wall 85 which is sloping and leads to the interior of said container 81.

Between the slot 83 for the delivery of the nails 17 of the vibrating feeder and the throughgoing zone or path of the slider 48 is disposed a substantially vertical ruler-like guiding bill 88 which is made up of an upper part 89 fixed to the sidewall and of a lower part 90 which is hinged at 91 with said upper part 89 with a pivoting axis parallel to the respective sidewall.

The half bill 89 and the half bill 90 have on the front side a vertical slot 92 with a T-shaped cross section. Into the upper end of said slot 92 fall the nails which, due to an appropriate and not shown profile, fall horizontally with the respective nail head within the cross leg of said T- shaped cross section of the slot 92 and with the respective nail stem into the long leg of said T-shaped slot and then the nails slide downwards in an horizontal position by gravity forming a continuous nail column in said vertical slot 92.

At the lower end of the lower half bill 90 is provided a release or drawing and synchronism unit or means for a single and reliable separation or drawing of the nails supplied in said nail column, and more specifically always the last nail of the column is drawn. Said unit 105 consists of a front drawing wheel 94, Figs. 23 and 24, the horizontal shaft 95 of which is rotatory supported in a bore 96 of said half bill 90 and is placed in the vertical middle plane of said T-shaped groove 92, as well as of an associated star wheel 98. On the periphery of the drawing wheel 94 is provided a number of housing grooves 97, in the example four, which extend according to generating lines, are spaced from each other with said nailing pitch P and are dimensioned such as to receive a single nail 17. For the rotation of the drawing wheel 94 with the latter co-operates a synchronism means for synchronizing the return motion speed of the slider 48 with the nail drawing speed of the drawing wheel 94, that is the delivery speed for bringing a single nail 17 into a respective underlying housing 57 of said slider 48. Said synchronism means consists, in the shown example, of a star wheel 98 which is keyed in a cantilevered manner on said shaft 95 of the drawing wheel 94 on the rear side of the lower half bill 90.

Said star wheel 98 has a number of rays 99 equal to the number of grooves 97 of the drawing wheel 94, whereby said rays 99 cover radially the imaginary rays of said grooves 97.

The upper strip 55 of the slider 48 is provided, on its vertical side facing said star wheel 98, with a plurality of pins 100, Fig. 24, which project laterally from the slider and are spaced longitudinally from each other with said nailing pitch P such as to cause, co-operating with said rays 99, a correct positioning of the respective lower groove 97 of said wheel 94 just above, a housing 57 of the slider 48, as explained in the following.

In order to create said mutual covering positioning between the drawing wheel 94 and the slider 48 for charging the nails into said slider housings as well as to remove said drawing wheel 94 from the slider 48 for interrupting said charging of the nails into the slider housings, said swivellable half bill 90 is connected with an arm 103 associated with an actuator 101, in the example a pneumatic cylinder-piston unit which is supported on the respective sidewall, Fig. 18. In order to secure the reliable practically covering positioning between a respective housing groove 97 of said drawing wheel 94 in the lower position and the respective underlying throughgoing slider housing 57, and therefore to assure the reliable fall by gravity of the nails, with its head below, into said slider housings 57 is provided a springy means which performs said relationship. In the shown example said means consists of semicircular seats 102; Fig. 24, which are provided on the periphery of the shaft 95 of the drawing wheel 94 and the star wheel 98, and more specifically are spaced from each other with equal radial distance. Said seats 102 co¬ operate with a not shown ball housed in a not shown cross bore provided in said half bill 90, whereby said ball is elastically biased by a spring by means of a screw which is housed, in a not shown manner, in said cross bore.

The to and fro strokes of said slider between the starting position C and the nail discharging position D inside the working station are controllable in a known manner by means of limit switches of which the switch 107 is shown. Said limit switches are fixed to a respective sidewall and co-operate with cams 109 secured to the slider 48, Fig. 21. On the slider 48 is fiirther provided another not shown cam co-operating with a sensor 113 which is supported on the respective sidewall in a longitudinally movable manner and fixes, throgh the actuator 101, the swinging instant of said half bill 90 in said covering position above the slider during the slider return stroke into the starting position, that is the instant in which begins the charging of said nails 17 into the slider housing 57.

By changing the position of said sensor 113 it is therefore possible to adapt the number of nails 17 to be inserted into the slider 48 to the length of the respective or associated side of the frame. The swingable movement for removing said drawing wheel 94 from above the slider 48, Figs. 9 and 24, takes place automatically when the slider arrives in its starting position, by means of the cam 111 and the associated limit switch, Fig. 21.

For lowering the wooden frame the invention provides on each sidewall 3, 4, 5 and 6 a shaft 115 which is longitudinally supported in a swingable manner on the upper face of said sidewall, and more specifically swivellable in both directions. This is accomplished for example with a pinion 117 keyed on the shaft 115 and meshing with a rack 118 connected to the piston of an hydraulic cylinder-piston unit 114, fig. 9.

On the shaft is fixed, with a separable swivellable taking engagement, a plurality of lowering or pressing arms 119 spaced from each other. Said spacing is indipendent from the nailing pitch and is arranged in such a manner to reliable press on the frame corner zones taking into consideration the wholly dimensional range of the frames to be nailed. Each pressing arm 119 is provided in detail, Figs. 19 and 22, at the shaft-side end thereof with a bore housing a fixing screw for mounting and fixing said arm onto said shaft 115, preferably with the interposition of setting elastic circlips or the like per se known and not shown. At ist free end 121 each pressing arm is provided with a pressing protrusion 122 which is able to engage the external or upper face 123 of the frame 11. The end 121 has further a bent part 124 which is bent at 90° and acts as a stop for the internal vertical face of said frame 11. In the shown embodiment the arms 119 are executed with telescopic stems 127 having securing screws.

Furthermore, in order to quickly adapt said arms 119 to the two most usual widths of the frame sides, in a bore 128 near said bending 124 is housed with clearance a screw 129 supporting a ferromagnetic small block 130. In the bent part 124 is lodged a supporting magnet 131. The block 130 is movable from a projecting active position, which is suitable for frames having narrow sides, to an inactive collapsed position, for frames having wide sides, whereby in the latter case become active the internal surface of said bent part 124.

Said arms 119 are swivellable from an open starting position, Fig. 19, in which the arms are completely away from the area of the working station, arid a pressed or closed position, Fig. 22, in which the frame 11 with the underlying canvas 10 are pressed from the supporting position

A to the nailing position B.

For the ejection of the nailed frames are provided known and not shown cylinder-piston units which are vertically fixed inside the working station beneath the nailing plane 8. Said ejection can also be facilitated by means of profiled elastic blocks or pads 45 as described in the following.

For the preliminary bending of the corners of said canvas 10 onto the frame are provided the known and not shown swivellable elements.

As nailing units 14 are provided, for example, mechanical units, Fig. 19, having a nailing rod 15 fixed to a rank slide 140 slidably supported in said sidewalls and meshing with a pinion 141 keyed on a throughgoing shaft 142. Said shaft 142 is freely swivellable supported on the top face of a respective sidewall and is driven by a known rank group 143 controlled by the cylinder-piston unit 144, Fig. 9.

Since the available hydraulic, pneumatic and electrical control circuits and the component thereof can be executed in a number of configurations well known to the specialist, has been omitted a detailled description of said circuits and components.

The operation of the machine according to the present invention is the following.

With the machines for a range of frame sizes, that is with machines with movable sidewalls, first is accomplished, in a known manner, the adjusting process of the movable sidewalls 4, 5 and 6 in accordance with the size of the frames 11 to be nailed and then the necessary supporting tongues 12 inside the working station are connected together by means of the elastic cord-like elements 13. The nailing units 14 do not require any setting thereof as all said nailing units 14 of each sidewall 3, 4, 5 and 6 are always controlled simultaneously and together.

To each shaft 115 of each sidewall 3, 4, 5 and 6 then are fixed all the necessary pressing arms 119.

By the rotation of each shaft the remaining arms 119 which are not secured to the respective shaft will stay stationary in their open position. The blocks 130 will be positioned according to the frames to be nailed. The sliders 48 for the transfer of said nails 17 are in the starting position C and already house the nails which are necessary for the frame to be neiled.

The nailing step itself takes place in a known manner, however advantageously with only one operator who has now a free access to all the area above the working station 7 for placing correctly a canvas sheet 10 and then a frame 11 for a new working cycle. By pressing with both hands, and this as accident prevention measure, two not shown activation push buttons the operator will then control the lowering motion of the pressing arms 119 with the consequent lowering of the canvas 10 and the superimposed frame 11 from the position A to the position B and simultaneously fold and stretch the canvas. (The machine is provided indeed with four activation push buttons, two thereof for each operator when two operators are employed for nailing large frames.) Due to the high friction between the friction tab 35 and the canvas 10 and the springy and increasing thrust action of the elastic pads 45 behind the tongues 12 during the lowering movement of the frame 11 the canvas is compelled to slide on the frame outwardly and upwardly. Therefor, in the lower nailing position B the canvas is strongly stretched on the frame 11. During the^* canvas and frame lowering stroke H from the position A to the position B the slider 48 has accomplished his transfer stroke from the starting position C to the position D inside the working station 7 for discharging the nails 17 into the nailing units 14. At the end of the nail transfer stroke the projecting end 67 of the diaphragm 56 and the stop element 64 of the latter impact with the opposite sidewall and the stop step 47, shown in Fig. 13, of the sidewall, respectively, with the consequent back motion of the diaphragm 56 into the slider 48 and the consequent coaxial vertical alignement of the slider housings 57 and 58 with the receiving chambers 19 in the sidewall so that the nails 17, Fig. 3, after the back movement of the nailing rods 15 fall into the nailing bores 18 and are intercepted by the magnets 16 and supported by the latter in the horizontal insertion position. The feed movement of said nailing rods 15 causes in a known manner the driving of the nails 17 into the canvas and the frame 11, thereby realizing the nailing step of the frame 11.

After discharging the nails 17 the slider 48 begins its return and nail charging stroke as follows.

At the begin of the return stroke the spring 65 causes again the exit movement of the diaphragm 56 and therefore the lower closure of said housings 57 of the slider 48. The swivellable lower half bill 90 is swivelled in disengagement from the sliding path of the slider 48. The subsequent swivellable movement towards the sliding path of the slider 48, and therefore the begin of the nail transfer into the slider housings 57 will take place depending on the dimension of the frame 11 to be nailed. With other words, while for the largest frame which can be nailed it is necessary to insert the nails 17 in all said housings 57 of the slider 48 (whereby the number of said housings corresponds to the number of the nailing units 14 to be charged with nails in the respective sidewall), for smaller frames are necessary less nails. This fact is taken into consideration by correspondently adjusting the adjustable sensor 113. Because the nails are inserted into the slider during the return stroke thereof (and the nailing step in the working station 7 takes always place starting from the slider front end ~ on the side of the diaphragm projecting end 67 — the insertion of the nails from the swivellable half bill 90 will take place either from the slider rear housing 57 (in the case of the largest frame which can be nailed) or from an intermediate housing 57 depending on the respective associated side length of the frame to be nailed. This adjustement takes place simply by displacing in a correspondent manner the adjustable sensor 113 along a guide for the latter which is provided longitudinally on the sidewall. Physically this takes place in that this adjustable sensor 113 causes the swivellable movement above the transfer path of the slider 48. This effects simultaneously the activation of the nail drawing wheel and the synchronism star wheel 98 which constrains the nail supplying speed to the slider speed.

In the illustrated embodiment when the actuator 101 causes the swivellable movement of the half bill 90 above the sliding path of the slider, that is above the slider 48 itself, the star wheel 98 comes into the movement path of the pins 100 fixed to the slider 48. The length and the profile of the rays 99 of said star wheel 98 is such that each pin during the slider return stroke comes into contact with a ray 99 and pushes the latter ~ thereby causing the rotation of said ray ~ for an amount corresponding to the nailing pitch P, and at the end of said amount the engament between the positioning ball and a respective seat 102 defines a reliable temporary stop of the star wheel 98 as well as of the drawing wheel 94. This enables the nail 17 in the housing groove 97 above the housing of the underlying passing through slider 48 to reliable fall with the head ^"downwards into said housing 57. In practice in order to facilitate and ensure a reliable nail fall into the housing 57 the latter are lightly profiled in an elongated and countersunk fashion. After charging all the housings 57 which are necessary according to the considered frame (the last charged housing is the anterior slider housing 57) the slider is in the starting position C for the next nailing step. The cam 111 with the respective microswitch 108 controls the swivellable return stroke of the half bill 90 in order to avoid an impact between the star wheel 98 and the pins 100 during the subsequent stroke of the slider 48, that is during the transfer of the slider 48 from the starting position C in the discharging position in which latter takes place the discharging of the nails 17 into the receiving chambers 19.

After the nailing process the frame 11 is strongly pressed in the working station 7 between the supporting tongues 12 and the elastic pads 45. Nevertheless the frame ejection, effected by means of per se known cylinder-piston units, takes place in a sweet manner with a mutual sliding extraction movement between the tab 35 and the leaf 36 of the supporting tongues 12, whereby said tab 35 and leaf 36 slip with a low friction the one against the other. During said mutual slipping movement said tab and leaf are in contact together only in the zone where the pads 45 and the wooden frame face each other, whereas said tab and leaf disjoin themselves and spring plastically out of shape above and under said intermediate pad area, the surface of which decreases during the frame ejection movement, as shown in Figs. 31, 32 and 33. By adopting said measures it is possible to avoid the drawbacks of the known machines and can be achieved an unobjectionable canvas stretching even with non-expandable frames, which greatly encreases the application field of these machines. In the errib'odiment with opposite resilient blocks or pads 45 having a sloping front side to form a wedge facing the interior of the working station and directed toward the bottom it is advantageously possible to exploit the elastic force of the elastics 13 to efficiently assist the frame ejection movement after the nailing step like an automatic shakeout. Another preferred embodiment of the supporting and stretching tongues 12 is diagrammatically shown in Figs. 34 to 36. With this embodiment it is possible to obtain and mantain also during the nailing step a particularly strong stretching of the canvas.

With respect to the embodiment of the support and stretching tongues 12 illustrated in the foregoing description the embodiment of the tongues 12 shown in Figs. 34 to 36 differs substantially in that:

- the supporting tab 35 is shortened in its length and the weave 37 having a low coefficient of friction and fixed to the bottom of said supporting tab 35 projects from the free end thereof and has a bore 138 or hook for supporting a cord-like elastic T 3, and

- the slipping leaf 36 co-operating with said supporting tab 35 instead of being connected at both ends thereof with said supporting tab 35 is separated from the latter and is fixed, for example glued, to the front face 46 of a respective resilient block or pad 45.

In this embodiment the pad front face 46 is substantially parallel to the vertical wall 44 of the respective sidewall facing the working station 7. Furthermore, the upper margin of the slipping leaf 36 is bent towards the sidewall in order to sweet the impact between the supporting tab 35 and the slipping leaf 36 during the canvas and frame lowering step. With this embodiment is avoided whatever bending stress of the slipping, now stationary leaf 36 during the frame ejection and therefore is achieved an increment of the life of said supporting tongues 12. Also the tongue manufacturing is thus simplified. As weave can be advantageously employed a nylon leaf, a lorry tarpaulin ribbon or the like as previously stated. Also the shortening of the supporting tab 35 facilitates the extraction movement thereof from the slipping leaf during the frame ejection.

It is within the scope of the invention to replace single components with other technical and/or functional equivalent ones, as well as to utilize either separated or in combination the solutions concerning the automatic nail feeding, the configurations of the supporting tongues and the means for lowering the canvas and the frame. With the disclosed machine it is possible to efficiently achieve the stated object and to reach the pointed out advantages.

Claims

CLAIMS 1. A machine for tensioning and nailing a canvas on an artists' frame comprising:

- a working station (7) consisting of four frame-like arranged sidewalls (3, 4, 5, 6) fixedly or adjustable supported on a machine frame (1), whereby each sidewall supports a plurality of support and tensioning tongues (12) adapted to support and engage an edge strip of said canvas (10) with a respective superimposed frame (11), whereby said tongues (12) at the ends thereof projecting in the working station (7) are connected together chess-board-like by cord-like elastics (13) defining with said tongues (12) a supporting plane for a canvas (10) and a superimposed frame (11),

- a plurality of nailing units (14) in each sidewall (3, 4, 5, 6), whereby each of said nailing units (14) is disposed horizontally in alignment with a respective nailing bore (18) provided in said sidewalls, whereby in each of said nailing bores (18) leads a vertical throughgoing nail receiving chamber (19) provided in sain sidewalls (3, 4, 5, 6),

- swivellable elements arranged in the corner of the working station (7) for preliminary folding the canvas corner zones on the frame (11),

- means for lowering said canvas (10) and superimposed frame (11) into a nailing plane (8), and

- means fixed to said sidewall (3, 4, 5, 6) inside the working station (7) for upwardly ejecting the nailed frame from the nailing plane (8), characterized in that

- said supporting and friction tongues (12) have different coefficients of friction on the opposite large faces thereof, that is a high coefficient of friction on the upper faces supporting the canvas (10) and a low coefficient of friction on the lower faces, - in that iή^'each sidewall (3, 4, 5, 6) are provided a vibrating nail feeder (49), a to and fro movable slider (48) for an automatic nail transfer from said vibrating nail feeder (49) in said throughgoing receiving chambers (19) located in the working station (7), as well as nail drawing means (94) for singularly drawing the nails from said nail feeder (49) and inserting said nails (17) into housings (57) in said slider (48) with associated synchronism means (98) for synchronizing the nail drawing speed with the slider stroke speed, and

- in that said canvas and superimposed frame lowering means comprises, for each sidewall (3, 4, 5, 6), a longitudinally supported shaft (115) operatively connected to a reversible swivellable driving means (114, 117), whereby said shaft (115) supports a number of lever-shaped lowering arms (119) at one end thereof and said arms are adapted to be removably secured to said shaft (115), and said lowering arms (119) at their free end have a lowering surface (122) engaging the above side (123) of the frame and a stop surface (124) co-operating with the internal vertical face of the frame sides.

2. A machine according to claim 1, wherein each of said tongues (12) is formed

- of an upper supporting tab (35) having a high coefficient of friction and to the bottom of which is fixed a substantially non-stretchable weave (37) having a low coefficient of friction, and

- of a lower slipping leaf (36) having a low coefficient of friction, whereby said supporting tab (35) and said slipping leaf (36) are in a facing relationship and are fixed together at their ends, or

- said slipping leaf (36) is fixed to a respective sidewall (3, 4,5, 6) directly or indirectly by the interposition of a resilient block or elastic pad (45) which latter, in turn, is fixed to said sidewall.

3. A machine according to claim 2, wherein at least a part of the front side (46) of said elastic pads (45) facing the respective opposite sidewall is wedge-like sloping downwards and towards the interior of said working station (7) or said front side (46) is parallel to the vertical side (44) of the respective sidewall.

4. A machine according to claim 1, wherein said nail transfering slider (48) is to and fro longitudinally movable on the respective sidewall (3,

4, 5, 6) and is connected to a to and fro means (70) for driving said slider (48) and adapted to impose to the latter a reciprocating movement between a starting position (C) outside said working station (7) and a discharging position (D) which lays over said nail receiving chambers (19) and inside said working station (7),

- wherein said transfer slider (48) comprises an upper strip (55) and an inferior diaphram (56) which, have both a number of vertical throughgoing housings (57, 58) corresponding to the number and to the pitch (P) of said throughgoing receiving chambers (19) provided in the sidewalls (3, 4, 5, 6),

- wherein said diaphragm (56) is supported on the bottom side of said upper strip (55), and is longitudinally slidable in a limited way and contrary to a spring means (66) which is adapted to realize an outgoing movement (F) of the front end (67) of the diaphragm (56) from the front end of the upper strip (55) for such a length (F) that, outside of said discharging position (D), said throughgoing housings (57, 58) of the upper strip (55) and the diaphragm (56) are vertically offset from each other and the diaphragm closes below the throughgoing housings (57) of said upper strip (55).

5. A machine according to claim 4, wherein at the end of the tranfer stroke of the slider (48) inside the working station (7) the respective opposite sidewall acts as a stop element for said slider (48) and realize, contrary to ^'said preloading spring means (66), the retracting movement of said diaphragm (56) and the vertically coaxial positioning between said throughgoing slider housings (57, 58) and said underlying nail receiving chambers (19) in the sidewalls (3, 4, 5, 6),

6. A machine according to claim 4, wherein said means for sliding said transfer slider (48) comprises a toothed transmission belt (70) which is turned over round between two sprocket wheels (71, 72) forming a driving section of the belt (70) parallel to the respective sidewall and extending below the slider (48) in its starting position (C), whereby said driving belt (70) is connected to the slider (48) with a bracket (79) or the like and to one (72) of both sprocket wheels (71, 72) being associated a reversible drive motor (73) by means of a clutch (74) having an adjustable maximun couple,

- wherein said elastic means (66) causing the advanced positioning of the diaphragm free end (56) with respect to the slider upper strip (55) . comprises a spring (66) which is preloaded between a stop element (64) . secured to the diaphragm (56) and a stop element (65) secured to the slider upper strip (55), and

- wherein said diaphragm (56) is engaged with said slider upper strip (55) by means of a number of screws (59) which are screwed in the bottom of said upper strip (55) and the heads (60) of said screws (59) are lodged in slot-like depressions (62) provided in the diaphragm (56), whereby said depressions (62) have a rear end, in the slider feed direction, which is able to determine the outgoing stroke (F) of the diaphragm front end.

7. A machine according to claims 1 and 4, wherein on said slider upper strip (55) in addition to cams co-operating in a known manner with limit switches secured to the machine frame (1) and fixing the transfer stroke into the working station (7) and the return stroke into the starting position C) is provided a cam co-operating with a sensor (113) wich is supported longitudinally on the sidewall in a slidable adjustable manner in function of the nail number to be inserted into the slider housings (57) during the return stroke of the latter, whereby said sensor (113) is adapted to activate a controll actuator (101) controlling the swivellable movement of the supplying end of a ruler-like nail guiding bill (88) of said vibrating feeder (48).

8. A machine according to claims 1 and 4, wherein above said diaphragm (48) in said starting position (C), upstream of the first throughgoing housing (57) is disposed the supplying end of a ruler-like vertically swivellable bill (88) of said vibrating nail feeder (49),

- wherein said bill (88) is provided on its front side with a vertical groove (83) having a T-shaped cross section in which the nails (17) coming from the vibrating nail feeder (49) are housed horizontally by holding the heads thereof in the cross side of said T-shaped groove (83) and slide downwards by gravity in a column,

- wherein said bill (88) is formed of two halves (89, 90) which are hinged together (91) about an axis parallel to the respective sidewall, whereby the upper halfbill (89) and the nail feeder (49) are fixed to the respective sidewall,

- wherein at the bill supplying end are disposed in an operatively relationship said nail drawing means (94) and synchronism means (98) for synchronizing the speed of the slider movement and the nail drawing speed, and

- wherein a to and fro control means (101) is provided which is adapted to swing said bill supplying end, that is the lower half bill (90) between a nail charging position which lays above a line defined by said throughgoing housings (57) of the slider (48), during the slider return stroke and for an adjustable number of housings (57), and a swivellable disengagement position of the lower half bill (90), for stopping the nail supply, as well as during the subsequent transfer stroke of the slider

(48) in said nail discharging position (D) inside the working station (7).

9. A machine according to claim 4, wherein said vibrating nail feeder

(49) adjacent the upper end of its internal helicoidal feeding path (82) presents in the container wall an opening (84) for discharging the nails (17) supplied in a position different from the vertical one and with the nail head below, and wherein externally from said opening (84) in the container wall is provided a balcony-like wall (85) having a sloping bottom for guiding again the rejected nails (17) into the feeder container (81).

10. A machine according to claim 1, wherein said means (94) for drawing the nails (17) from the supplying end of said bill (88) comprises an anterior drawing wheel (94) which is rotatory supported in the bill (88) with a shaft (95) parallel to the long side of the T-shaped groove (92) and laying in the middle plane of said T-shaped groove (92), wherein on the periphery of said drawing wheel (94) is provided a number of housing grooves (97) for housing a respective nail (17) and which are equidistant from each other with the nailing pitch (P) and parallel to the wheel shaft (95), and

- wherein said synchronism means (98) comprises, on one side, a star wheel (98) which is cantilevered supported from behind on the drawing wheel shaft (95) and presents a number of rays (99) corresponding to the number of housing grooves (97), whereby said radially disposed rays (99) cover the imaginary rays of tha drawing wheel intersecting said grooves (97) and extend towards the slider (48) and, on the other side, a number of pins (100) fixed to the vertical side of the slider upper strip (55) adjacent to said star wheel (98), said pins (100) being arranged with the nailing pitch (P) and projecting beyond the rays (99) of said star wheel^{" '}(98) with such a length that, when the lower half bill (90) is swivelled above the slider, said pins (100) mesh with the star wheel rays (99) whereas, when the lower half bill (90) is swivelled away from the slider (48), said star wheel (98) is in disengagement from said pins (100).

11. A machine according to claim 10, wherein is provided a springy positioning means defining the correct relative positioning between said nail housing grooves (97) and the slider nail receiving housings (57), and wherein said means comprises semicircular seats (102) provided on the periphery of the shaft (95) of the drawing wheel (94) and the star wheel (98), which seats (102) are distributed with an equal angular spacing corresponding to the nailing pitch (P) and co-operate with a ball which is housed in a corresponding cross bore of the lower half bill (90) and is elastically biased by a spring by means of a screw in said swivellable lower half bill (90).

12. A machine according to claim 1, wherein said lowering arms (119) at their driving shaft-side end are provided with a circular housing for mounting said arms (119) on said driving shaft (115) and co-operate with removable fixing means, and wherein said lowering arms (119) have at their free end a bending (124) which defines said lowering and stopping surfaces (122, 124), said arms (119) having a telescopic stem

(127) which can be clamped by means of screws.

13. A machine according to claim 12, wherein to an internal side of said arm bending (124) is removably supported one or more spacers (130) for the adaptation to the width dimensions of the frame sides, and wherein said adaptation spacers (130) consist of ferromagnetic material and are supported by a screw (129) housed with clearance in a bore

(128) of the stem (127) near the bending (124), and wherein in said bent side (124) is lodged a magnet (131) which holds the adaptation spacer (130) movable in two positions thereof.