GB1599418A

GB1599418A - Safety guards for machine tools

Info

Publication number: GB1599418A
Application number: GB1772477A
Authority: GB
Original assignee: Udal Ltd J P
Current assignee: Udal Ltd J P
Priority date: 1977-05-03
Filing date: 1977-05-03
Publication date: 1981-09-30

Description

(54) SAFETY GUARDS FOR MACHINE TOOLS (71) We, J. P. UDAL LIMITED, a British Company of 133-155 Tyburn Road, Birmingham B24 8NJ, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to safety guards for machine tools, and of the kind comprising a movable bar over which an operative must reach in order to gain access to the movable parts of the machine, said bar being biased away from the machine, and means whereby the machine tool is rendered inoperative unless the bar is far enough away from the movable parts of the machine to prevent an operative having his hands or arms in a position of danger in relation to the movable parts of the machine.

Such guards are normally used with machine tools such, for example, as presses where it is necessary to feed sheet metal to the tools of the machine, and for this reason the bar is disposed at, or below the height of the tools so that the sheet can be fed over the bar.

Heretofore, in safety guards of this kind the bar has usually been carried by a pair of arms mounted upon pivots near, and secured to, the floor, so that the bar moves through an arc away from the machine thereby reducing the height of the bar as it moves from the machine, and rendering it easier for an operative to reach over the bar to a position of danger.

The object of the present invention is to overcome this disadvantage by providing a bar which will move away from the machine at a substantially constant height, and which can be carried from the machine to avoid the necessity for mounting pivots on the floor.

According to the invention a safety guard for a machine tool, and of the kind specified is characterised in that the bar is carried by, and extends between a pair of similar links of a pair of similar lazy tongs mechanisms, each lazy tong mechanism having another link pivoted on a framework adapted to be connected to the machine tool, and a further link carrying a roller movable within a track on the framework.

One example of the invention as applied to a power press will now be described with reference to the accompanying drawings in which Figure 1 is a side view of the mechanism, Figure 2 is a fluid circuit and Figure 3 shows a modification of a portion of the mechanism seen in Figure 1.

Referring to the drawings, secured to the press (not shown) is a framework including a pair of frames, (one of which is seen at 10) secured to opposite sides of the press. On each frame 10 is pivoted at 11 the first link 12 of a lazy tongs mechanism. A second link 13 of the lazy tongs mechanism is pivoted at its midpoint intermediate the ends of the link 12 at 14, and carries its lower end, a roller 15 movable within a channel section track 16 mounted on the frame 10. The opposite end of the link 13 is pivotally connected at 17 to a third link 18 of the lazy tongs mechanism, whilst the other end of the link 18 is pivotally connected at 19 to an intermediate point of a fourth link 20 of the mechanism.One end of the link 20 is pivotally connected at 21 to the end of the link 12 remote from the pivot 11, whilst the other end of this link carries a bar 22 extending between it and the complementary link of the other lazy tongs mechanism.

Also pivotally mounted at 11 on the frame 10 is a quadrant 23 having a series of arcuately arranged holes 24 through any one of which the link 12 can be connected to the quadrant by means of a bolt. The quadrant 23 is connected to an arm (not shown) extending radially from the pivot 11 and connected at its outer end to one end of a coiled tension spring (not shown) the other end of which is connected to a fixed point in the lower part of the frame 10. The quadrant 23 is thereby loaded in a clockwise direction as viewed in Figure 1, so as to urge the lazy tongs mechanism into an extended direction in which the bar 22 is removed from the press. The amount of extension of the lazy tongs mechanism can be varied by selecting the appropriate hole 24 for connection of the quadrant to the link 12 by means of the bolt.

Each lazy tongs mechanism may have a quadrant and spring associated therewith.

The pivots 14, 17, 19 and 21 may con veniently be formed at the side of rods extending between the two lazy tongs mechanisms so as to prevent an operative from gaining access to the press tools from under the bar 22 which should normally be at about waist height of an operative and slightly below the height of the lower press tool.

The reference 25 represents a pedal control of the press which requires to be depressed in order to initiate an operative stroke of the press. In the present example, this pedal control 25 is arranged to be actuated by a pedal 26 operable by the machine tool operator. The pedal 26 is pivoted at 27 and is connected to an arm 28 the outer end of which is connected to the one arm of a bellcrank lever 29 (pivoted at 30 on a fixed part), through a link 31 incorporating collapsible member in the form of a piston and cylinder unit 32, the other arm of the bellcrank lever 29 being connected through an adjustable link 33 to the pedal control 25.

Pneumatic pressure is normally admitted to the unit 32 through a pair of valves 34 and 35 (Figure 2) arranged in series so as to cause the unit 32 to act as a solid portion of the link 31. However, should either of the valves 34, 35 be actuated to exhaust the cylinder of the unit 32, depression of the pedal 26 will not effect depression of the pedal control 25 to start the press. The valves 34 and 35 are arranged to be actuated resptectively by the two quadrants 23 when the bar 22 is moved towards the press from a safe position, thereby preventing the operator from starting the press when he is too close to the latter for safety.

In order to maintain the pedal 26 in a raised position when the cylinder of the unit 32 is exhausted, the arm 28 is connected to the pedal control 25 by coiled tension spring 36.

When the pedal 26 is depressed it is arranged to actuate a valve 37 in series with the valves 34, 33 to admit pneumatic pressure to a pair of cylinders 38 and 39. When pneumatic press ure is admitted to the cylinders 38 and 39, their respective pistons are moved outwardly and thereby move latches (one of which is seen at 40) into a position to block anti-clockwise movement (as seen in Figure 1) of the quad rants 23 and thereby prevent the bar 22 from being moved towards the press whilst the press is in operation.

In order to improve the effectiveness of the safety guard it is constructed so as to be sensitive to forces applied to the bar 22 whilst the machine is in operation and whilst the latches 40 are in the operative position. Press ure applied to the bar as for instance by an operator leaning on the bar will impart hori zontal and/or downward forces to the bar.

Sensitivity to horizontal forces is provided by allowing a small gap between the opposing faces of the quadrants 23 and latches 40 when the bar 22 is fully extended. When horizontal force is applied to the bar the gaps are closed and it is arranged that the movement of the quadrant in the anticlockwise direction is sufficient to actuate the valves 34, 35 thereby releasing the pedal control 25 of the press.

The sensitivity to downward force is obtained by the modification which is shown in Figure 3. In Figure 3 the channel 16a in which slides the roller 15, is pivotally mounted at its upper end on the frame 10 at a pivot point 40a. The extent of pivotal-movement of the channel is determined by a pin 41 secured to the frame 10 and which is located within a slot 42 formed in the base of the channel.

A spring biasing unit 43 is provided to load the channel 16a in the clockwise direction to a position determined by the pin 41. The strength of the spring incorporated in the unit 43 is such that it can maintain the channel in this position against the force imposed by the roller 15 on the channel, even when the bar 22 is in its furthest position from the press. If an operator leans on the bar and applies a downward force thereto, an increased force is applied to the channel 16a and if this force is sufficiently large the channel will move in the anti-clockwise direction an amount as allowed by the slot 42. A further valve 44 is provided having its operating member engaging the channel and the further valve is included in the fluid circuit shown in Figure 2, conveniently in series with the valves 34 and 35.In operation the valve 44 only allows air flow as described when the channel is in the position as shown in Figure 3, i.e., when little or no downward pressure is applied to the bar by the operator.

In some instances it is desired to use electrical switches in place of the valves. In such circumstances the piston cylinder combinations are controlled by solenoid actuated valves connected in the electrical circuit of the switches.

In the arrangement described the bar 22 is biased outwardly away from the press by means of a spring or springs associated with the quadrant or quadrants. The outward biasing of the bar may be achieved by the used of gravity.

For this purpose the dispositions of the pivotal connections of the lazy tongs mechanisms and the rollers with the frames are inverted. If this modification is effected then gravity will exert a force to displace the bar outwardly away from the press. The sensitivity to horizontal forces and to downward forces applied to the bar 22 can be obtained in a similar fashion. Increased downward force will cause more pressure to be applied to the channel and this can be pivotally mounted and spring biased so as to function in a similar manner to that described with reference to Figure 3.

WHAT WE CLAIM IS:- 1. A safety guard for a machine tool and of the kind specified characterized in that the bar is carried by, and extends between a pair of similar links of a pair of similar lazy tongs mechanisms, each lazy tong mechanism having

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. veniently be formed at the side of rods extending between the two lazy tongs mechanisms so as to prevent an operative from gaining access to the press tools from under the bar 22 which should normally be at about waist height of an operative and slightly below the height of the lower press tool. The reference 25 represents a pedal control of the press which requires to be depressed in order to initiate an operative stroke of the press. In the present example, this pedal control 25 is arranged to be actuated by a pedal 26 operable by the machine tool operator. The pedal 26 is pivoted at 27 and is connected to an arm 28 the outer end of which is connected to the one arm of a bellcrank lever 29 (pivoted at 30 on a fixed part), through a link 31 incorporating collapsible member in the form of a piston and cylinder unit 32, the other arm of the bellcrank lever 29 being connected through an adjustable link 33 to the pedal control 25. Pneumatic pressure is normally admitted to the unit 32 through a pair of valves 34 and 35 (Figure 2) arranged in series so as to cause the unit 32 to act as a solid portion of the link 31. However, should either of the valves 34, 35 be actuated to exhaust the cylinder of the unit 32, depression of the pedal 26 will not effect depression of the pedal control 25 to start the press. The valves 34 and 35 are arranged to be actuated resptectively by the two quadrants 23 when the bar 22 is moved towards the press from a safe position, thereby preventing the operator from starting the press when he is too close to the latter for safety. In order to maintain the pedal 26 in a raised position when the cylinder of the unit 32 is exhausted, the arm 28 is connected to the pedal control 25 by coiled tension spring 36. When the pedal 26 is depressed it is arranged to actuate a valve 37 in series with the valves 34, 33 to admit pneumatic pressure to a pair of cylinders 38 and 39. When pneumatic press ure is admitted to the cylinders 38 and 39, their respective pistons are moved outwardly and thereby move latches (one of which is seen at 40) into a position to block anti-clockwise movement (as seen in Figure 1) of the quad rants 23 and thereby prevent the bar 22 from being moved towards the press whilst the press is in operation. In order to improve the effectiveness of the safety guard it is constructed so as to be sensitive to forces applied to the bar 22 whilst the machine is in operation and whilst the latches 40 are in the operative position. Press ure applied to the bar as for instance by an operator leaning on the bar will impart hori zontal and/or downward forces to the bar. Sensitivity to horizontal forces is provided by allowing a small gap between the opposing faces of the quadrants 23 and latches 40 when the bar 22 is fully extended. When horizontal force is applied to the bar the gaps are closed and it is arranged that the movement of the quadrant in the anticlockwise direction is sufficient to actuate the valves 34, 35 thereby releasing the pedal control 25 of the press. The sensitivity to downward force is obtained by the modification which is shown in Figure 3. In Figure 3 the channel 16a in which slides the roller 15, is pivotally mounted at its upper end on the frame 10 at a pivot point 40a. The extent of pivotal-movement of the channel is determined by a pin 41 secured to the frame 10 and which is located within a slot 42 formed in the base of the channel. A spring biasing unit 43 is provided to load the channel 16a in the clockwise direction to a position determined by the pin 41. The strength of the spring incorporated in the unit 43 is such that it can maintain the channel in this position against the force imposed by the roller 15 on the channel, even when the bar 22 is in its furthest position from the press. If an operator leans on the bar and applies a downward force thereto, an increased force is applied to the channel 16a and if this force is sufficiently large the channel will move in the anti-clockwise direction an amount as allowed by the slot 42. A further valve 44 is provided having its operating member engaging the channel and the further valve is included in the fluid circuit shown in Figure 2, conveniently in series with the valves 34 and 35.In operation the valve 44 only allows air flow as described when the channel is in the position as shown in Figure 3, i.e., when little or no downward pressure is applied to the bar by the operator. In some instances it is desired to use electrical switches in place of the valves. In such circumstances the piston cylinder combinations are controlled by solenoid actuated valves connected in the electrical circuit of the switches. In the arrangement described the bar 22 is biased outwardly away from the press by means of a spring or springs associated with the quadrant or quadrants. The outward biasing of the bar may be achieved by the used of gravity. For this purpose the dispositions of the pivotal connections of the lazy tongs mechanisms and the rollers with the frames are inverted. If this modification is effected then gravity will exert a force to displace the bar outwardly away from the press. The sensitivity to horizontal forces and to downward forces applied to the bar 22 can be obtained in a similar fashion. Increased downward force will cause more pressure to be applied to the channel and this can be pivotally mounted and spring biased so as to function in a similar manner to that described with reference to Figure 3. WHAT WE CLAIM IS:-

1. A safety guard for a machine tool and of the kind specified characterized in that the bar is carried by, and extends between a pair of similar links of a pair of similar lazy tongs mechanisms, each lazy tong mechanism having

another link pivoted on a framework adapted to be connected to the machine tool, and a further link carrying a roller movable within a track on the framework.

2. A guard according to Claim 1, in which the bar is biased away from the machine in use by resilient means.

3. A guard according to Claim 2, in which said resilient means comprises a coiled spring which is adjustably connected to one of said mechanisms.

4. A guard according to Claim 3, including a quadrant pivotally mounted about a pivot carrying one of said other links on the frame, said quadrant having means for selectively coupling the quadrant to said one of said other links, said quadrant being connected to an arm the end of which is connected to the coiled spring.

5. A guard according to any one of the preceding Claims, in which the tracks are pivotally mounted on said framework, each track having spring means associated therewith, said spring means yielding in the event that downward pressure is applied to the bar to permit limited angular movement of the tracks and means for sensing such movement to prevent starting of the machine tool.

6. A guard according to Claim 5, including stop means for restricting movement of the bar towards the machine tool once operation of the machine has been initiated.

7. A guard according to Claim 6, including means for sensing movement of the bar towards the machine tool said means when such movement is sensed whilst said stop means is in operation, acting to prevent starting of the machine tool.

8. A guard according to Claim 1, including a control member operable by the operator, the machine tool including movable means which when moved from an inoperative position to an operative position causes operation of the machine tool, and linkage means connecting said control member with said movable means, said linkage means incorporating a collapsible member which only when the bar is in its outermost position is rigid to transmit the movement of the control member to the movable means.

9. A guard according to Claim 8, in which said collapsible member comprises a piston cylinder unit which is supplied with fluid under pressure to make it rigid.

10. A guard according to Claim 9, including a valve for controlling the supply of fluid to the piston cylinder combination, said valve being operable directly or indirectly by a part of the guard when the bar has been moved to its outermost position.

11. A guard according to Claim 9, including means operable when the control member is actuated by the operator to lock the bar in its outermost position.

12. A guard according to Claim 1 in which the bar is biased away from the machine to its outermost position by the action of gravity.

13. A safety guard for a machine tool sub stantially as hereinbefore described with reference to the accompanying drawings.