1. Field of the Invention
The invention relates to a wrench, more particularly to a torque-indicating wrench with excellent precision.
2. Description of the Related Art
U.S. Pat. Nos. 6,928,885 and 6,948,380 disclose electrical torque-indicating wrenches that generally have strain gages attached to a handle for measuring the torque. The location of the strain body in the handle is normally close to a head's position, wherein the head is used to engage and rotate a workpiece by applying a force to the handle. The strain gages detect the elastic strains and the changes in electrical resistances, and translate the changes into an electrical signal, in cooperation with a processing circuit, the strain gages can determine a value of torque applied to the workpiece.
Refer to FIGS. 1 and 2, 3-D assembly views of a conventional electrical torque-indicating wrench, which comprises a head 211, at least one strain body 218, a strain gage unit 212 located on each strain body 218, a processing circuit 213, a display unit 214, and a stem 215. The strain gage unit 212 includes several strain gages 219. The stem 215 includes an outer longitudinal surface 216 (in FIG. 1) or a recess slot 217 (as shown in FIG. 2). The strain gage unit 212 can be replaced when one of the strain gages 219 is broken, and strain body 218 is attached to the outer longitudinal surface 216 or a surface of the recess slot 217 of the stem 215. When a torque is applied to the head 211, a torque is produced to induce stretching deformation (applying the tensile force) on the strain gages 219 resulting in a change of the electrical resistance, which can be detected and translated into an electrical signal. After processing the electrical signal in the processing circuit 213, the processed electrical signal will then be transferred into readable data showed on the display unit 214.
Since the conventional torque-indicating wrenches is designed with the strain body 218 in contact with the outer longitudinal surface 216 or the recess slot 217 of the stem 215, during the stretching deformation, the strain body 218 would slide against to the surface of the stem 215, as a result, the contact portion between the strain body 218 and the surface of the stem 215 is unstable. In addition, according to FIG. 1, the strain body 218 is designed with a flat-shaped structure, the strain body 218 would be seriously sliding against the stem 215 while stretching the strain body 218. As a matter of fact, the combination of the strain body 218 and the stem 215 would cause the torque-indicating wrenches becoming very unstable to perform the task, such as, inaccurate measurements would be obtained, and the errors would occur in the electrical signal resulting the correct torque value could not be obtained.