## 1 Introduction  
Recently, there has been increasing interest among researchers in remote robot systems with force feedback [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. In the systems, a user can remotely control a robot by manipulating a haptic interface device while perceiving the reaction force from an object touched or moved by a robot arm equipped with a force sensor. We can expect to significantly improve the efficiency and accuracy of remote operations, as the user is able to physically sense the shape, weight, and softness of the object [7; 8; 9; 10; 11; 12; 13]. Consequently, remote robot systems with force feedback can be utilized in environments that are hazardous or inaccessible to humans, such as disaster-stricken areas, nuclear power plants, deep-sea exploration, and outer space [11]. Nevertheless, when haptic data such as position and/or force information is transmitted over a non-guaranteed Quality of Service (QoS) [17] network, like the Internet, Quality of Experience (QoE) [18] might be greatly affected. Therefore, it is essential to clarify the influence of network delay, delay jitter, and packet loss on the operation and to study efficient QoS control [11; 19; 20]. On the other hand, [PERSON] et al. investigated the effects of two users controlling an avatar compared to one user controlling an avatar to move in a virtual space [21]. Their experimental results showed that the performance with two users was superior to that of one user. In [22], [PERSON] et al. proposed a \"virtual co-embodiment\" in which a virtual avatar is controlled by two users (one is a teacher, and the other is a learner) for motor skill learning. Experimental results indicated that using the proposed method enhances the efficiency of motor skill learning. Therefore, in order to clarify if dual-user operation is more effective than single-user operation for cooperation in a remote robot system with force feedback, the authors in [23] compare single-user and dual-user operations, where an object is collaboratively carried by two remote robot systems with force feedback. The results indicates that dual-user operation outperforms single-user operation regarding the force acting upon the object. Additionally, when two users experienced different network delays, the user with the lower network delay can help the other user [23]. However, the reasons why the user with the lower network delay can help the other user remain unclear, and it is necessary to clarify this mechanism. Additionally, in [23], the authors calculate the position vector of a robot by simply averaging the two position vectors of haptic interface devices in the robot position control, which is used to determine the position of the remote robot arm for dual-user operation. It is crucial to evaluate how varying the ratios of the two position vectors affects the calculation of the robot's position vector. Furthermore, from [23], it is observed that the force acting upon the object increases with the escalation of network delay. When the applied force becomes large, it may be difficult for the user to do collaborative work. Furthermore, if the force exerted is too large, the object could be damaged. It is important to reduce the applied force as network delay increases by considering enhancements to the QoS control employed in [23]. Therefore, in this paper, we focus on dual-user operation, which may be more efficient than single-user operation in remote robot systems. First, we examine the effects of network delays on dual-user operation and measure the force applied to the object by changing the network delays between the remote robot and the two users to clarify the underlying mechanisms. In the experiment, we use robot position control, which is a type of QoS control employed in [23] that adjusts the robot position using the positions of the two users' haptic interface devices. Next, we propose an enhancement method for the robot position control by taking network delays into account to reduce the applied force.