Due to the numerous pipetting operations in the experiment, our laboratory consumes a large number of pipette tips daily, which makes the workload of loading pipette tips heavy. In response to this problem, we tailored hardware for the pipette tips and pipette tip boxes used in our laboratory to load the pipette tips. The hardware model was designed on Autodesk Fusion 360, and we 3D-printed the designed solid file to assemble our hardware. Our hardware is mainly divided into two parts: the main body and the tip comb. Considering that the tip box used in our laboratory can hold 12*8 tips in total, there are 12 slots on the main body, and the tip comb has 8 teeth.

The hardware usage process is as follows:
1. Pour about 100-200 tips into the main body.
2. Hold the handles on both sides of the main body and shake them back and forth. During the shaking process, you can tap the main body to speed up this step until you observe that most of the pipette tips are vertical in the main body slot.
3. Insert the tip comb along the hole of the main body bracket, paying attention that the long side of the tip comb enters the side hole, and the short side is aligned with the middle hole.
4. Align the pipette tips with the hole in the tip box, and put the main body down so that the tip enters the tip box.
5. Pull out the tip comb, open the cover next to the main body, and slide the main body to make the tip enter the tip box.

With the help of this hardware, it takes about 90s to insert a whole box of tips, which saves time and effort and reduces the workload for students.

Mechanical Analysis

The main principle of the hardware is to make the pipette tips not leak in the groove of the main body but be arranged vertically during vibration. We call the junction of the head and body of the tip as neck, where the diameter of the tip has a noticeable change. With this feature, we designed the beam of the main hardware body that separates each groove to be narrow at the top and wide at the bottom, which makes the groove wide at the top and narrow at the bottom, so that the pipette tips can be stuck on the beam with the neck upright without leaking. This requires that the inner diameter of the upper part (wider part) of the groove of the main body is larger than the diameter of the head, and the inner diameter of the lower part (narrow part) of the groove is shorter than the diameter of the head and larger than the diameter of the neck.

To achieve the above effects, we should consider not only the geometry of the tip we use but also the possible deformation of the main beam. Due to cost constraints, we can only use softer resins for 3D printing. Therefore, the rigidity of the beams separating each groove in the hardware body may be not big enough, which may cause the tip to leak from the slot. To solve this problem, we optimized the geometric parameters of the main hardware body through calculation and enhanced the beam of the main body to the inflexibility that can meet the requirements for using and saving materials.

Under the assumption of little deformation, the deformation equation of the beam is

$$\frac{d^2w}{dx^2}=\frac{M}{EI}$$

w is the deformation quantity at x, M is the moment of force in the beam at x, E is the material's elastic modulus, and I is the cross-sectional inertia moment of the beam. After consulting, the elastic modulus of the resin we use is about 25GPa, and the cross-sectional moment of inertia is 0.656m4 after calculation. Assuming that a force F is applied at the midpoint of the beam (the force applied to the middle of the beam will produce the maximum deformation), we can obtain the deformation diagram of the beam through the above simulation as follows. It can be seen that the maximum deformation does not exceed 0.15mm/N. Considering the light weight of the pipette tip, we conservatively estimate that the deformation of the middle of the beam does not exceed 0.05mm, and the change of the inner diameter of the main groove will not exceed 0.1mm, which is entirely acceptable.