Gripper for strapping machine

Abstract: A device for applying various levels of gripping force to a lead end (7) of a strap during various phase of a strapping cycle of a strapping machine includes a gripper (1) and anvil (4) and a cam (6). The cam (6) has high pressure (15,22), reduced pressure (17,19) and released pressure surfaces (16,18) to grip the strap (7) firmly, loosely, or not at all, depending on the requirements of the strapping cycle.

Description: The present invention relates to the gripping of a strap end before and during the tensioning phase of a strapping machine. At present, as shown for example in document US-A-4 383 881, strapping machines exert a single, generally high level gripping force on the lead end of a strap to secure the strap end during the slack removal and tensioning phase, prior to strap sealing, of the strapping machine cycle. However, application of a high gripping force to the strap end during the rest phase of the strapping cycle, prior to the tensioning phase, increases the difficulty of pulling the strap out of the gripper if necessary, to clear a strap jam, change over the strap, or rewind the strap coil. According to a first aspect of this invention a multiple stage gripping apparatus for a strapping machine, comprises: an end gripper means, an anvil, and a gripper cam, the gripper cam having a first cam surface for urging the end gripper means against a section of a strap lead end to secure firmly the strap lead end between the end gripper means and the anvil, a second cam surface for releasing the gripping force and a third cam surface for generating a reduced gripping force for securing the strap lead end in a removable manner, wherein the gripper cam is rotated to engage the various cam surfaces during a strapping cycle. According to a second aspect of this invention a method for gripping a strap in a machine comprises the steps of: urging one cam surface against a cam bearing to urge a tooth of an end gripper against a section of a strap lead end to secure the strap lead end loosely in a fixed position during a rest phase of a strapping cycle, and urging another cam surface against the cam bearing to urge the tooth of the end gripper against the section of a strap lead end to displace the section of the strap lead end into an anvil recess to secure the strap lead end firmly in a fixed position during a tensioning phase of a strapping cycle. The end gripping device of the present invention allows for the easy removal of a lead strap end from the gripping device except during the tensioning stage. Preferably it provides a two force end gripping device which exerts a high gripping force on a lead end of a strap for the tensioning phase, and a reduced gripping force at other phases of a strapping cycle and more during strap loading. Such an arrangement exerts a reduced gripping force on a lead end of a strap to prevent the strap from bouncing back or rebounding from a sensing lever after contacting with the lever. A preferred embodiment of a strapping machine in accordance with this invention will now be described with reference to the accompanying drawings; in which:- Figure 1 is a sectional view in the insertion phase. Figure 2 is a secontional view in the rest phase. Figure 3 is a sectional view in the tensioning phase. Figure 4 is a side view of a three position cam of the present invention. Figure 5 is a side view of a four position cam of the present invention. Shown in Figure 1 is the gripping apparatus of a strapping machine in the pre-grip phase of the strapping cycle. An end gripper 1 in communication with a gripper spring 2 is driveable by a force acting on cam bearing 14. Gripper cam 6 is rotatable to present various cam surfaces to the cam bearing. A gripper tooth 3 may be disposed at a terminal end of the end gripper 1. An anvil 4 is position adjacent to the end gripper 1 in a manner which allows a strap lead end 7 to be inserted through a strap path 21 between the anvil 4 and the end gripper 1. The anvil 4 includes an anvil recess 5 which houses a strap limit sensing lever 8. A tooth anvil gap 11 in the anvil 4 receives the gripper tooth 3 during the gripping phase and may receive the gripper tooth partially during the rest phase. The strap separator 12 adjacent the anvil 4 and the end gripper 1 receives the strap in an integral strap path in the separator 12. In Figure 2, the end gripper 1 is shown in a low or soft grip position, where the strap lead end 7 has travelled to and tripped the limit sensing lever 8. The strapping machine is in a rest phase of the strapping cycle at this point. The gripper cam 6 has at this time rotated to urge a particular surface of the cam 6 against the cam bearing 14, which moves the end gripper 1 against the strap in a manner which holds the strap in place, but would allow the removal of the strap without the necessity of repositioning the end gripper. This gripping mode eliminates the problem of strap recoil or bounce back after contact of the strap lead end 7 with the limit sensing lever 8, by fixing the strap in place immediately at the moment the lead strap end trips the limit sensing lever 8. Also, a machine operator may easily strap from the end gripper 1 during this phase, because of the carefully adjusted soft grip condition achieved by the device. This facilitates the procedures of strap jam clearing, strap change over, and strap coil rewinding. Figure 3 shows the end gripper 1 in the tensioning phase. Gripper cam 6 has been rotated to urge a particular surface of the cam 6 against the cam bearing 14, which moves the end gripper against the strap in a manner which holds the strap in a semi-permanent position. Gripper tooth 3 is urged against the strap, pushing a segment of the strap into the tooth anvil gap and against the anvil surface of the tooth anvil gap, firmly gripping the strap in place. The strap will at this phase remain gripped as the strapping machine executes the tensioning phase. Figure 4 shows one embodiment of the gripper cam 6. First cam surface 15 is urged against the cam bearing 14 just prior to and during the tensioning phase. Second cam surface 16 is urged against the cam bearing 14 during the rest or home position phase of the strapping cycle, providing a soft grip condition. Figure 5 shows another embodiment of the gripper cam 6. Cam surface 22 is urged against the cam bearing 14 during the tensioning phase. Cam surface 18 is urged against the cam bearing 14 during the period at which the strap must be held in a soft grip condition, for example to briefly prevent the bouncing or rebound of the strap lead end. Subsequently, cam surface 20 is urged against the cam bearing 14, dropping the end gripper 1 to release the grip force. Next, just before and also during the tensioning phase, cam surface 22 is urged against the cam bearing 14.

Claims: A multiple stage gripping apparatus for a strapping machine, comprising: end gripper means (1), an anvil (4), and a gripper cam (6), the gripper cam (6) having a first cam surface (15,22) for urging the end gripper means (1) against a section of a strap (4) lead end (7) to secure firmly the strap lead end (7) between the end gripper means (1) and the anvil (4) and a second cam surface (16,18) for releasing the gripping force and characterised in that it utilises a third cam surface (17,19) for generating a reduced gripping force for securing the strap lead end (7) in a removable manner, wherein the gripper cam (6) is rotatable to engage the various cam surfaces during a strapping cycle. A multiple stage gripping apparatus according to claim 1, wherein the gripper cam (6) also includes a fourth cam surface (20) for releasing the gripping force located between the third (19) and first (22), cam surfaces. A multiple stage gripping apparatus according to claim 1 or 2, wherein the end gripper means (1) has an end gripper (3) at a distal end and, the anvil (4) has a tooth anvil gap (11), wherein the end gripper (1) is urged by the gripper cam (6) against the strap lead end (7) at a section, deforming the strap (7) and gripping the strap (7) between the end gripper tooth (3) and a surface of the tooth anvil gap (11). A strapping machine including a gripping apparatus in accordance with any one of the preceding claims. A method for gripping a strap in a machine characterised by the steps of: urging one cam surface (17,19) against a cam bearing (14) to urge a tooth (3) of an end gripper (1) against a section of a strap lead end (7) to secure the strap lead end (7) loosely in a fixed position during a rest phase of a strapping cycle, and urging another cam surface (15,22) against the cam bearing (14) to urge the tooth (3) of the end gripper (11) against the section of a strap lead end (7) to displace the section of the strap lead end into an anvil recess (11) to secure the strap lead end (7) firmly in a fixed position during a tensioning phase of a strapping cycle.

Inventors: HABERSTROH JAMES, RENZ MARK, HABERSTROH, JAMES, RENZ, MARK
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1996
Main classification: B65B13
IPC codes: B65B13