03.3 Design Process
1. Initial design iteration (Brainstorming)
1.1. The 1 -DOF claw
1.2. Gantry-arm-claw combined system
1.3. Different gripper mechanism designs
Current design in Fig. 3a uses slider-crank mechanism, it has pros and cons as follows:
Pros:
● Self-centered motion ensures both jaws move symmetrically, reducing misalignment when grasping objects
● Compact and lightweight
● Predictable kinematics; single input variable defines full motion path
Cons:
● Limited grip force as mechanical advantage decreases as jaws fully close
● Frictional losses in small revolute joints that may reduce precision
● Limited payload size relative to gear-based or cam-driven alternatives
The alternative design in Fig. 3b replaces the linkage actuation in Fig. 3a with two meshing gears that directly rotate the gripper arms. A central pinion driven by a motor produces synchronized mirrored motion of both jaws. This design allows for high torque transfer and precise angular positioning, beneficial for heavier payloads or tighter controls.
Pros:
● Increased torque capacity enables handling of heavier or stiffer objects.
● High positional accuracy due to direct gear engagement
● Easier to integrate with rotary servos or stepper motors for fine control
Cons:
● Manufacturing tolerance sensitivity – 3D printed gears may have backlash or even meshing
● Increased noise and wear under continuous cycling
1.4. Horizontal translation system design
Horizontal translation is achieved via a motor-driven pinion engaging a linear rack. As the pinion rotates, it converts rotary motion into linear displacement of the platform, moving it along the x-axis. A linear guide rail ensures stability and eliminates out-of-plane movement.
Pros:
● High positional precision and repeatability for controlled linear motion
● Rigid structural support – the guided track prevents lateral or vertical deflection
● Scalable – easy to extend travel length by increasing rack length
Cons:
● Manufacturing tolerance sensitivity – 3D printed gears may have backlash or even meshing
● Gear wear overtime can degrade positioning accuracy
● Requires precise alignment between pinion and rack to avoid binding
● No inherent holding torque – power loss can cause unintended direct unless locked
1.5. Different arm extension system designs
Concept 1: Slider-Crank
The mechanism in Fig. 5a converts rotary motion into vertical linear displacement in the y-direction through a slider-crank linkage. A rotating crank, L3, drives a connecting rod that moves a slider vertically, providing a defined lift stroke.This mechanism would be mounted on a prismatic base in order to allow for the x-axis translation.
Pros:
● Reliable and well-understood motion profile with predictable output path
● Smooth sinusoidal motion, ideal for repetitive lifting cycles
● Mechanically efficient – minimal energy loss through friction compared to cables in a pulley system.
Cons:
● Fixed stroke length determined by crank radius; limited adjustability
● Nonlinear vertical profile – slower at extremes, faster mid-stroke
● Difficult to scale for longer vertical travel without redesigning linkage
Concept 2: Pulley system
In Fig. 5b, a motorized winch drives a cable wound around pulleys to raise and lower the vertical arm assembly. Bearings guide the rope to maintain tension and alignment, offering flexible travel length and smooth lifting.
Pros:
● Large range of motion achievable with minimal redesign
● Fewer rigid components making it lightweight
● Easily reversible motion by changing winch motor direction
Cons:
● Low positional precision due to cable stretch and slack
● Requires counterweights or tensioners for stability
● Safety concern if cable fails under load
Concept 3: Electric Linear-Control Solenoid
In Fig. 5c, a proportional-controlled solenoid provides direct linear motion, pushing and pulling the connected links and thus creating a scissor type extension/retraction along the y-axis. This type of solenoid has a responsive actuation based on the current input, allowing for variable actuation.
Pros:
● Fast response with minimal delay
● Compact and self-contained – no external linkages or pulleys
● Easy electronic control with PWM signals
● Low maintenance due to the absence of moving joints
Cons:
● Limited stroke length – adjusting it would require a new solenoid or shaft
● Force drop with distance – poor performance for long or heavy lifts
● Requires continuous power to maintain actuation (no self-locking)
● Low efficiency compared to pulley or slider-crank for sustained loads
2. Prototype iteration
2.1. Iteration 1 - 2D claw
2.2. Iteration 2 - 3D claw
2.3. Iteration 3 - Incorporated with other subsystems
3. Final iteration
3.1. Horizontal translation
The mechanism chosen for the horizontal translation is a screw bolt (also referred to as a helical joint). This allows for translation, but also rotation. To prevent rotation, two rods were used, and a 3D-printed trolley connects the rods and the screw bolt together. This trolley also allows for mounting of the robotic arm extension and motors.
TR lead screws were used with the trolley, and linear bearings were used to fasten the trolley to the rods while allowing smooth translation. A TR lead screw was also used with custom 3D-printed mounts to attach a continuous-rotation (360) servo motor. This allows full translation of the trolley, extension arm, and claw along the full length of the rail.
End supports were 3D-printed to hold the rails and the screw bolt. Rotational bearings were used for the screw bolt to allow free rotation. The end supports were then fastened to aluminum extrusion rails to form the gantry structure.
3.2. Extension arm
The final iteration of the arm module still adopts the crank–slider lifting scheme shown in Fig. 10. Since our actuator is a rotary motor, the motor rotation must be converted into a linear input to drive the mechanism. Therefore, the motor directly rotates a crank link, which pushes/pulls a slider constrained on a linear guide rail. The vertical position of this slider is then transmitted to the linkage below, resulting in a smooth up-and-down motion of the arm. In this way, a single motor can precisely control the arm’s lifting stroke while keeping the motion compact and mechanically robust.
3.3. Grasping claw
The final iteration of claw still follows the slider-crank design shown in Fig. 3a. Since we only have rotary motors, we need transform the motor rotation into the linear input to the slider. So we add an rack-and-pinion mechanism to drive the linear slider (L4). Then through slider-crank mechanism it controls the open and close of the fingers.