Electromagnetic holding device

A probe head of a coordinate measuring apparatus for interchangeably holding probe pins each having an armature so as to permit the probe pin to be held by magnetic force, the probe head comprising:

• a holding member;
• a displaceable part mounted in said holding member so as to be displaceable with respect thereto;
• a holding device mounted in said displaceable part for engaging, holding and releasing the probe pin, the holding device including:
• a flux-conducting member defining an annular gap;
• permanent magnetic means having a permanent magnetic field for acting on the armature of a probe pin with a holding force to hold the probe pin on said holding device;
• electromagnetic means for superposing an electromagnetic field on said permanent magnetic field when the probe pin is transferred to or away from said holding device;
• said electromagnetic means being seated in said annular gap and said electromagnetic field defining a magnetic field axis;
• said permanent magnetic means defining magnetic poles and being seated in said gap so as to cause said magnetic poles to be aligned radially of said field axis;
• and,
• said armature and said flux-conducting member conjointly defining a contact engaging interface when said probe pin is in position on said holding device so as to cause said flux-conducting member and said armature to define a completely closed magnetic circuit for the field lines of said electromagnetic field.

A probe head for a coordinate measuring apparatus for interchangeably holding a plurality of probe pins each having an exchange plate defining an armature, the probe head comprising:

• a holding member;
• a displaceable part defining a longitudinal axis and being mounted in said holding member so as to be displaceable with respect thereto;
• resilient biasing means disposed in said displaceable part for generating a resilient biasing force;
• an electromagnetic chuck mounted in said displaceable part so as to be movable along said axis and against said resilient biasing force;
• the electromagnetic chuck including:
• a flux-conducting part having a longitudinal axis and defining an annular gap;
• permanent magnetic means having a permanent magnetic field for acting on the armature of a probe pin with a holding force to hold the probe pin on said chuck;
• electromagnetic means for superposing an electromagnetic field on said permanent magnetic field to strengthen the latter when transferring a probe unit onto said chuck and for superposing an electromagnetic field on the permanent magnetic field in opposition thereto to weaken the latter when transferring the probe pin off said chuck;
• said electromagnetic means being seated in said annular gap;
• said permanent magnetic means defining magnetic poles and being seated in said gap so as to cause said magnetic poles to be aligned radially of said longitudinal axis of said flux-conducting part;
• and,
• said permanent magnetic means being stacked in said gap on top of said electromagnetic means so as to cause said permanent magnetic means to be directly adjacent said armature when the probe pin is held on said chuck.