Servo - May 2015

80 SERVO 05.2015

are rubber-lined, whereas the VEX gripper has two concave curved gripper fingers that are also rubber lined. On first glance, with its two parallel sides, this type of gripper would seem to be ideal for grasping flat objects or items with two flat and parallel sides. Parallel jaw grippers do have one disadvantage when trying to grasp an object: The sides of the two fingers/pincers of the gripper may not exactly grab the sides of a square object due to a slight difference in ‘parallelism.’ This will allow the object to twist and swivel on the two points of contact. Having a bit of ‘slop’ in the construction of the two jaws and the drive gears, or having compliant rubber lining on the jaws will allow full contact on both sides. The Robotiq gripper shown in Figure 11 utilizes a unique finger configuration to perform as a parallel jaw or V-jaw gripper. There are numerous styles, quality, and prices of grippers that can be found on major robotics manufacturer’s sites and the overseas Internet sites you can find when Googling “robot grippers.” ServoCity offers a line of four grippers shown in Figures 12A to 12D priced from $6.99 to $14.99. I would highly recommend that any robot designer peruse the pages of the servocity.com site to look at the many hundreds of photographs showing mechanisms, structures, bearings, and, of course, mountings for all sorts of mechanisms including these grippers.

Even if you don’t intend to purchase any of their products, you will most certainly see drawings and photos that will make you say “why didn’t I think of that?” I have collected most of the photos into one file that I refer to on many occasions when I am trying to design something.

The V-Jaw Angle Robot Gripper

One of the most common types of gripper is the type that is formed by two pincers opening and closing as a “V” — like our fingers. The ServoCity micro gripper utilizes a Hi Tec HS- 5055MG or similar sub-micro servo and is a great gripper for small to tiny robots. The ServoCity perpendicular gripper is well suited for a mid-sized robot, and the perpendicular oriented servo mounting allows for a slender arm structure.

The ServoCity horizontal gripper utilizes the same V-gripper design as the previous two with a horizontally mounted servo, and they both can be adapted to ‘standard’ Hi Tec or Futaba servos.

All of these grippers are well designed and built from stout 1/4” ABS plastic. ServoCity also has a mobile robot with an arm and gripper that they call the Stacker (shown in Figure 13) that I have yet to try out.

These grippers will always grasp an object in two points, and the object may swivel like the above parallel jaws.

Again, the use of a rubber compound on the faces of the two fingers may stabilize the grasped object. I used two soft rubber replacement handle covers for needle-nose pliers on the jaws of the V-jawed gripper on the robot in Figure 9.