## 2 Existing Research
### Peg-Hole Insertion Connector Technique  
A general peg-hole is also a ubiquitous method that involves the analysis of force during the mating process. As in other insertion methods, a positioning error results in a reaction force between the surfaces, which causes some damage [2]. Various researchers have adopted different approaches to compensate for the reaction forces. Simultaneously, [PERSON] [3] presented the situation of jamming, absorbed between two surfaces by utilizing compliance devices to compensate for the reaction force and avoid damage. He used variable remote center compliance (VRCC), which had a shear pad of elastomers to alter the center of the compliance during the insertion, owing to the reaction force. [PERSON] [4] utilized remote center compliance (RCC) to compensate for the reaction force. The material also offered a greater force required to complete the insertion process. A few other research studies adopted the active method in the peg-hole approach by utilizing Gaussian mixture regression to copy the movement of a human hand in the lead by teaching and implementing a force control strategy for autonomous insertion [4]. In addition, [PERSON] [5] utilized the error recovery strategy from the size information of the connector and adjusted the compliance motion for successful mating of the four-pin plug-in connector. The most common technique for peg-hole insertion is Blind Search. There are other blind search strategies, such as the spiral, probing, and binary trajectory techniques. The tilt strategy was selected in the peg-hole insertion when no visual system was available for assistance [6]. Due to its design, blind search strategies and passive method techniques have been widely applied to these macro systems. However, these techniques cannot be utilized directly at the micro-level, as there is a vast difference in the design of connectors. Connector mating has three categories: (1) arriving, (2) exploring, and (3) mating. [PERSON] utilized a four-pin plug-in connector to analyze the assembly task and proposed four search algorithms based on force/moment data [7]. The four search algorithms are as follows: (1) spiral search, (2) probing search, (3) binary search I, and (4) binary search II. These algorithms indicated the relationship between the change in force based on the misalignment during insertion, followed by error recovery. [PERSON] and [PERSON] [8; 9] proposed a hybrid vision-force-guided system for a four-pin plug-in connector. [PERSON] [5] stated a combination of vision and force on the fault inspection online. It improves the rate of detecting the system's error and makes it more robust when utilizing the data provided by the force and vision system. First, the vision system takes an image as an ideal case, uses it as a benchmark, and compares the rest of the image with this benchmark image. It determines the change in coordination with both images and predicts the fault in grasping. Therefore, if the grasping is not straight, there will always be some error in insertion, owing to the small space available for insertion. It has an extra step in detecting the vision system's connector for grasping. The tilting strategy combined with impedance control can overcome the position error caused by the vision system in the grasping procedure. To overcome the challenge of [5], \"iHand-designed\" was explicitly utilized for connector grasping and achieved an insertion rate of 99 % [10]. This particular type of gripper helps predict the distance variation with the connector. It detects the deformation in the PCB. [PERSON] [11] designed a gripper for accurate alignment and for analyzing the permissible tolerance range of plug-in connectors. [PERSON] also [12] tested 70 plug-in connectors