Safety mechanism for materials handling system

1. A safety lock comprising:

a locking member which engages a support;

an inner lock shaft for actuating said locking member, said inner lock shaft having a first coupling face at one end thereof;

an outer lock shaft having a second coupling face which is engagable with said first coupling face when said outer lock shaft is in an engagement position relative to said inner lock shaft;

a coupling structure which moves to prevent engagement of said first coupling face with said second coupling face by moving said outer lock shaft away from said engagement position relative to said inner lock shaft.

2. A safety lock according to claim 1 , wherein said locking member is a wedge or a caliper.

3. A safety lock according to claim 1 , further comprising a lock collar in which said locking member is situated, wherein actuation of said locking member prevents movement of said lock collar along said support.

4. A safety lock according to claim 3 , further comprising a coupling box secured to said lock collar and moveable thereto, said inner lock shaft held by said lock collar, said outer lock shaft held by said coupling box.

5. A safety lock according to claim 4 , wherein flexible members secure said coupling box to said lock collar.

6. A safety lock according to claim 4 , wherein said outer lock shaft is linearly stationary relative to said coupling box.

7. A safety lock according to claim 3 , wherein a counterbalanced load is coupled to said lock collar.

8. A safety lock according to claim 7 , wherein said coupling box is secured to said lock collar via a friction block which is rigidly attached to said coupling box, said load situated between said friction block and said coupling box.

9. A safety lock according to claim 7 , wherein said load is a test head.

10. A safety lock according to claim 1 , further comprising a spring loaded handle coupled to said outer lock shaft, said spring urging said first coupling face and said second coupling face apart.

11. A method of locking a load, said method comprising the steps of:

operating an outer lock shaft and thus causing an inner lock shaft to cause a locking member to engage a support when respective first and second coupling faces of said inner lock shaft and said outer lock shaft are positioned for being engagable with each other; and

operating said outer lock shaft without causing said inner lock shaft to disengage said locking member from said support so that said load remains locked when said respective first and second coupling faces of said inner lock shaft and said outer lock shaft are positioned away from being engagable with each other.

12. A method of locking a load according to claim 11 , wherein said locking member is a wedge or a caliper which engages said support.

13. A method of locking a load according to claim 11 , wherein said locking member is situated in a lock collar, a coupling box is secured to said lock collar and is movable thereto, said inner lock shaft is held by said lock collar, and said outer lock shaft is held by said coupling box, said inner lock shaft and said outer lock shaft are away from engagement with each other when said coupling box moves relative to said lock collar.

14. A method of locking a load according to claim 13 , wherein said coupling box moves relative to said lock collar when counterbalancing of a load coupled to said coupling box changes.

15. A method of locking a load according to claim 11 , wherein a spring urges said first coupling face and said second coupling face apart.