Force detector

A force detector comprising:

• a support;
• a first fluid container, a second fluid container, a third fluid container, and a fourth fluid container supported by the support, including a bag shape defined by a sheet-shaped member, and disposed adjacent to each other;
• a contact portion disposed opposite to a side on which the first fluid container, the second fluid container, the third fluid container, and the fourth fluid container are in contact with the support and disposed adjacent to all the first fluid container, the second fluid container, the third fluid container, and the fourth fluid container;
• a detector configured to detect an internal pressure of the first fluid container, an internal pressure of the second fluid container, an internal pressure of the third fluid container, and an internal pressure of the fourth fluid container;
• and
• a computer configured or programmed to obtain information regarding the internal pressure of the first fluid container, the internal pressure of the second fluid container, the internal pressure of the third fluid container, and the internal pressure of the fourth fluid container from the detector and, upon application of an external force to the contact portion from an object, calculate a force acting in a tangential direction on a contact surface between the object and the contact portion;
• wherein
• upon application of the external force to the contact portion from the object, the external force applied to the contact portion from the object is imparted to all the first fluid container, the second fluid container, the third fluid container, and the fourth fluid container through the contact portion;
• and
• when a sum of internal pressures of two fluid containers of the first fluid container, the second fluid container, the third fluid container, and the fourth fluid container is defined as a first internal pressure and a sum of internal pressures of the other two fluid containers of the first fluid container, the second fluid container, the third fluid container, and the fourth fluid container is defined as a second internal pressure, upon application of the external force to the contact portion from the object, the computer calculates the force acting on the contact surface in the tangential direction based on a difference between the first internal pressure and the second internal pressure.