Patent ID: 7244091

Claim:
A robot arm mechanism comprising: a first arm including first and second long parallel links each having a supporting end portion and a driving end portion and substantially in parallel relationship with each other, a first short parallel link intervening between the supporting end portions of said first and second long parallel links and a second short parallel link intervening between the driving end portions of said first and second long parallel links substantially in parallel relationship with said first short parallel link, said first long parallel link, said second long parallel link, said first short parallel link and said second short parallel link being pivotably connected with one another to collectively form a quadric crank chain; a second arm including a link having a handling end portion and a connecting end portion pivotably connected with said supporting end portion of said first long parallel link of said first arm; a link retaining mechanism having a reference line, said link retaining mechanism pivotably retaining said first arm and said second arm respectively and keeping a first angle substantially equal to a second angle, said first angle being an angle formed by a line passing through said driving end portion of said first long parallel link of said first arm with said reference line, said second angle being an angle formed by a line passing through said handling end portion of said second arm with said reference line; and a robot arm driving mechanism including a first driving shaft operative to rotate said driving end portion of said first long parallel link of said first arm around a rotation axis in any one of two rotation directions consisting of a first rotation direction in which said first arm and said second arm are extended, and a second rotation direction in which said first arm and said second arm are contracted, whereby said robot arm driving mechanism is operative to rotate said first long parallel link of said first arm around said rotation axis in said first rotation direction, and said second short parallel link of said first arm around said rotation axis in any one of two directions consisting of said first rotation direction and said second rotation direction while keeping said first and second short parallel links of said first arm forward in said first rotation direction in comparison with said first and second long parallel links of said first arm by maintaining said first angle less than a third angle formed by a line passing through said second short parallel link of said first arm with said reference line in said first rotation direction.