1. Field of the Invention
This invention relates to apparatus for marking a workpiece and, more particularly, to a method and apparatus for supporting a marking device for selective movement on a frame to position the marking device to selectively impress identification marks on the surface of the workpiece.
2. Description of the Prior Art
Impact type marking devices are well known in the art of impressing identification marks on the surface of stock being conveyed in a production line. One well known application is the use of marking machines that carry marking elements, either alpha or numeric characters, into impact relation with the surface of a workpiece to impress an array of characters on the workpiece as it is being conveyed in a production line. The devices disclosed in U.S. Pat. Nos. 3,541,954; 3,636,871 and 4,036,127 are representative of these types of marking machines which are used to impress identification marks on the surface of stock material, such as billets, slabs, plates, bars, ingots, and the like.
In the past, it has been the practice to utilize a single wheel marker that includes a plurality of marking elements or characters carried on the peripheral surface of the marking wheel. Such an arrangement is disclosed in U.S. Pat. No. 4,214,520. This type of marking device can be utilized to mark a wide variety of objects that vary in size from rolling stock in a production line to various metals, tags, components and parts.
It is also known to remotely control the operation of a single or multiple wheel marking machine to rotate the marking wheel to place a desired character in position for impressing a mark on the surface of the object. The wheel is mounted in a frame which is capable of moving through various degrees of movement and to be locked in the desired location. Thereafter, an actuator, upon energization, moves the marking wheel to strike the workpiece and impress the selected mark on the surface thereof. The marking wheel is retracted, after which the wheels incrementally rotate and move laterally to the next position for marking the workpiece. Thus the actuator is sequentially operated to move the marking wheel along a preselected path to impress the desired series of characters on the workpiece. The principal disadvantage to this type of marking device is that the choice of characters available for impressing a mark on the surface of the workpiece is limited by the characters carried on the periphery of the marking wheel. Also, depending upon the position of the characters on the marking wheel, delays are encountered in retracting the marking wheel and rotating the marking wheel to position the desired character in marking relation with the workpiece.
Therefore, the conventionally known single and multiple wheel type marking machines are not readily adaptable to rapid marking operations where a wide variety and combination alphanumeric characters are required to be impressed upon the surface of an object. The need for providing a rapid marking operation is particularly important in a production line where the marking device must be supported for rapid movement into and out of marking position and the character selection is also rapidly accomplished. Of principal importance is that the marking characters be rapidly changed on the marking device to permit marking a plurality of workpieces moving in rapid succession in a production line without interrupting the sequence of operations which take place in a production line due to delays encountered with the marking operation.
More recently, in an effort to increase the speed of the marking operation and to reduce the time required to change the combination of the alphanumeric characters for a message to be inscribed on a workpiece, noncontact markers, such as ink jet or spray printers, as well as dot matrix engraving machines have been utilized. Ink jet or spray printers are predominantly used to imprint on recording medium, such as paper. Examples of known ink jet or spray markers are disclosed in U.S. Pat. Nos. 3,787,884; 4,272,773; 4,356,499; 4,376,284; 4,412,232 and 4,415,909.
Programmable dot matrix printers are well known, such as is disclosed in U.S. Pat. No. 4,412,232. U.S. Pat. No. 4,415,909 discloses an ink jet printer which includes a print head movably supported along a line of print with the line of symmetry of the printhead being at an angle relative to the direction of motion. This arrangement produces a vertical column of dots perpendicular to the direction of movement. A nozzle array is formed in a pattern to generate equally separated rows of dots on the recording media. A drive element is associated with each nozzle, and a piezoelectric crystal initiates the formation of ink droplets which are ejected from the nozzle. The times for energizing the individual print elements are remotely controlled to minimize the gap between the nozzles in forming dot matrix type printing. U.S. Pat. No. 3,892,174 discloses a spray marking device operable to apply a dot matrix mark to an object moving along a conveyor. It is stated that the dots may also be represented by an impact mark. Electrical controls are provided to select the desired alphanumeric characters and to control movement of the object to be marked.
British Pat. No. 2,002,694 discloses a programmable dot matrix type of engraver for impressing a selected size of alphanumeric characters on a workpiece. The engraver is computer controlled to provide selective continuous marking of the workpiece to overcome the delays encountered with manual engravers. An engraving tool is supported on an arm which is movable on a carriage by a leadscrew rotated by a stepping motor. The carriage is movably mounted on a horizontal arm that is, in turn, supported by a vertical column above a base on which the workpiece to be marked is stationarily positioned. With this arrangement, the engraving tool is movable along horizontal X and Y axes. The engraving tool includes a punch which is remotely controlled by a central processing unit through a solenoid operated air valve to form the desired dot matrix character whereby the size of the figure engraved is determined by the number of stepping motor steps between each point of the 7.times.5 matrix. Furthermore, similar to the wire dot martix printers for computers, there is now also available an engraver with marking pins selectively actuated and arranged in a straight line configuration, which can form alphanumeric characters by collectively traversing a given number of lateral units. U.S. Pat. No. 4,506,999 entitled "Program Controlled Pin Matrix Embossing Apparatus" discloses pneumatically controlled apparatus that includes an array of pins utilized to emboss alphanumeric characters in an object. Seven pins move across the object and selectively mark the object with the desired characters. The angular arrangement of the pins determines the height of the characters and rotation of the head adjusts the angle of the line of pins. The angular adjustment is made manually by means of ball lock pins.
While it has been suggested by the prior art devices to utilize both contact and noncontact type dot matrix marking devices, there is need for an improved dot matrix type marking device that is computer controlled to rapidly mark the workpiece with a preselected alpha or numeric character and also a message that includes a combination of alphanumeric characters. The marking operation must be accomplished, particularly in a production line type of operation, without interfering with the other operations performed on the workpiece in the production line. The marking device must be capable of movement along multiple paths in a plurality of axes to enable selective positioning of the mark to be impressed on the surface of the workpiece. There is also need for a dot matrix type marking device for inscribing multiple lines of dot matrix characters on the surface of an object in rapid fashion and remotely controlling the size and the size change of the characters.