Immersion Corporation of San Jose, CA holds 142 US patents, nearly all of which are related to haptic human-computer interfaces.

From a conference call for Immersion shareholders: The case involved Immersion's allegation that Sony Computer Entertainment America, Inc. (SCEA) and Sony Computer Entertainment, Inc. (SCEI, the Japanese parent of SCEA) infringed 16 claims in
two of our patents, U.S. Patent Number 6,275,213 and 6,424,333, relating to vibro-tactile technologies. The case was filed on February 11, 2002 in the U.S. District Court for the Northern District of California. The case has been pending before United States District Judge Claudia Wilken.

It is worth noting that Microsoft was also named in this case on claims that the Xbox also infringed; they settled out of court.

Here's 6,275,213. It's interesting to note that this isn't even their patent, originally. It was assigned to a company named Virtual Technologies, out of Palo Alto.

Tactile feedback man-machine interface device

Abstract: A man-machine interface which provides tactile feedback to various sensing body parts is disclosed. The device employs one or more vibrotactile units, where each unit comprises a mass and a mass-moving actuator. As the mass is accelerated by the mass-moving actuator, the entire vibrotactile unit vibrates. Thus, the vibrotactile unit transmits a vibratory stimulus to the sensing body part to which it is affixed. The vibrotactile unit may be used in conjunction with a spatial placement sensing device which measures the spatial placement of a measured body part. A computing device uses the spatial placement of the measured body part to determine the desired vibratory stimulus to be provided by the vibrotactile unit. In this manner, the computing device may control the level of vibratory feedback perceived by the corresponding sensing body part in response to the motion of the measured body part. The sensing body part and the measured body part may be separate or the same body part.

U.S. Patent 6,424,333 is a continuation application of prior U.S. application Ser. No. 09/561,782, filed on May 1, 2000 now U.S. Pat. No. 6,275,213, in the name of Marc Tremblay, et al., which is a continuation of prior U.S. patent application Ser. No. 09/066,608, filed on Apr. 24, 1998 now U.S. Pat. No. 6,088,017, which is a continuation of U.S. patent application Ser. No. 08/565,102, filed Nov. 30, 1995, abandoned; and all of which are incorporated herein by reference.

From a law.com article in September 2004, here's a description of the alleged infringement:

He said the PlayStation technology in dispute "is a very small subset of vibrations" that occur in a joystick during a small number of events per game.

For example, he said, in "A Bug's Life," the ant in the game must jump first on an acorn, which then turns into a mushroom.

Powers said the vibration in question occurs only when the ant jumps on the mushroom several times.

From the same article, this quote was also amusing:

"It takes a special breed of person to enjoy watching great patent lawyers try a case, and generally that breed of person is ill," said Harold McElhinny, a patent litigation partner at Morrison & Foerster. "The dramatic skills for openings and cross-examinations don't appear quite as often in patent cases where the subject matter is colorless.

"I have to pay money to have my family come and watch me try a patent case," McElhinny joked.

Here's a complete list of Immersion's patents:

PAT. NO. Title
1 6,866,643 Determination of finger position
2 6,864,877 Directional tactile feedback for haptic feedback interface devices
3 6,859,819 Force feedback enabled over a computer network
4 6,850,222 Passive force feedback for computer interface devices
5 6,833,846 Control methods for the reduction of limit cycle oscillations for haptic devices with displacement quantization
6 6,822,635 Haptic interface for laptop computers and other portable devices
7 6,817,973 Apparatus for controlling force for manipulation of medical instruments
8 6,816,148 Enhanced cursor control using interface devices
9 6,801,008 Force feedback system and actuator power management
10 6,781,569 Hand controller
11 6,762,745 Actuator control providing linear and continuous force output
12 6,750,877 Controlling haptic feedback for enhancing navigation in a graphical environment
13 6,717,573 Low-cost haptic mouse implementations
14 6,715,045 Host cache for haptic feedback effects
15 6,707,443 Haptic trackball device
16 6,705,871 Method and apparatus for providing an interface mechanism for a computer simulation
17 6,704,683 Direct velocity estimation for encoders using nonlinear period measurement
18 6,704,002 Position sensing methods for interface devices
19 6,704,001 Force feedback device including actuator with moving magnet
20 6,703,550 Sound data output and manipulation using haptic feedback
21 6,697,748 Digitizing system and rotary table for determining 3-D geometry of an object
22 6,697,086 Designing force sensations for force feedback computer applications
23 6,697,048 Computer interface apparatus including linkage having flex
24 6,697,044 Haptic feedback device with button forces
25 6,697,043 Haptic interface device and actuator assembly providing linear haptic sensations
26 6,693,626 Haptic feedback using a keyboard device
27 6,693,622 Vibrotactile haptic feedback devices
28 6,686,911 Control knob with control modes and force feedback
29 6,686,901 Enhancing inertial tactile feedback in computer interface devices having increased mass
30 6,683,437 Current controlled motor amplifier system
31 6,680,729 Increasing force transmissibility for tactile feedback interface devices
32 6,661,403 Method and apparatus for streaming force values to a force feedback device
33 6,654,000 Physically realistic computer simulation of medical procedures
34 6,639,581 Flexure mechanism for interface device
35 6,636,197 Haptic feedback effects for control, knobs and other interface devices
36 6,636,161 Isometric haptic feedback interface
37 6,580,417 Tactile feedback device providing tactile sensations from host commands
38 6,564,168 High-resolution optical encoder with phased-array photodetectors
39 6,563,487 Haptic feedback for directional control pads
40 6,486,872 Method and apparatus for providing passive fluid force feedback
41 6,470,302 Interface device and method for interfacing instruments to vascular access simulation systems
42 6,469,692 Interface device with tactile feedback button
43 6,448,977 Textures and other spatial sensations for a relative haptic interface device
44 6,437,771 Force feedback device including flexure member between actuator and user object
45 6,429,846 Haptic feedback for touchpads and other touch controls
46 6,424,356 Command of force sensations in a forceback system using force effect suites
47 6,424,333 Tactile feedback man-machine interface device
48 6,411,276 Hybrid control of haptic feedback for host computer and interface device
49 6,400,352 Mechanical and force transmission for force feedback devices
50 6,380,925 Force feedback device with spring selection mechanism
51 6,374,255 Haptic authoring
52 6,366,273 Force feedback cursor control interface
53 6,366,272 Providing interactions between simulated objects using force feedback
54 6,353,850 Force feedback provided in web pages
55 6,353,427 Low cost force feedback device with actuator for non-primary axis
56 6,348,911 Force feedback device including safety switch and force magnitude ramping
57 6,343,349 Memory caching for force feedback effects
58 6,342,880 Force feedback system including multiple force processors
59 RE37,528 Direct-drive manipulator for pen-based force display
60 6,323,837 Method and apparatus for interfacing an elongated object with a computer system
61 6,317,116 Graphical click surfaces for force feedback applications to provide selection of functions using cursor interaction with a trigger position of a graphical object
62 6,310,605 Force feedback interface with selective disturbance filter
63 6,305,311 Kayak back-band installation assembly and method for installing a back-band in a kayak
64 6,304,091 Absolute position sensing by phase shift detection using a variable capacitor
65 6,300,938 Multiple-cylinder control device for computers and other electronic apparatus
66 6,300,937 Method and apparatus for controlling force feedback for a computer interface device
67 6,300,936 Force feedback system including multi-tasking graphical host environment and interface device
68 6,292,174 Enhanced cursor control using limited-workspace force feedback devices
69 6,292,170 Designing compound force sensations for computer applications
70 6,288,705 Interface device and method for providing indexed cursor control with force feedback
71 6,285,351 Designing force sensations for computer applications including sounds
72 6,281,651 Haptic pointing devices
73 6,278,439 Method and apparatus for shaping force signals for a force feedback device
74 6,271,833 Low cost force feedback peripheral with button activated feel sensations
75 6,271,828 Force feedback interface devices providing resistance forces using a fluid
76 6,259,382 Isotonic-isometric force feedback interface
77 6,256,011 Multi-function control device with force feedback
78 6,252,583 Memory and force output management for a force feedback system
79 6,252,579 Interface device and method for providing enhanced cursor control with force feedback
80 6,246,390 Multiple degree-of-freedom mechanical interface to a computer system
81 6,243,078 Pointing device with forced feedback button
82 6,232,891 Force feedback interface device having isometric functionality
83 6,219,033 Method and apparatus for controlling force feedback interface systems utilizing a host computer
84 6,219,032 Method for providing force feedback to a user of an interface device based on interactions of a controlled cursor with graphical elements in a graphical user interface
85 6,211,861 Tactile mouse device
86 6,201,533 Method and apparatus for applying force in force feedback devices using friction
87 6,195,592 Method and apparatus for providing tactile sensations using an interface device
88 6,191,774 Mouse interface for providing force feedback
89 6,184,868 Haptic feedback control devices
90 6,169,540 Method and apparatus for designing force sensations in force feedback applications
91 6,166,723 Mouse interface device providing force feedback
92 6,161,126 Implementing force feedback over the World Wide Web and other computer networks
93 6,154,201 Control knob with multiple degrees of freedom and force feedback
94 6,154,198 Force feedback interface apparatus including backlash and for generating feel sensations
95 6,147,674 Method and apparatus for designing force sensations in force feedback computer applications
96 6,131,097 Haptic authoring
97 6,128,006 Force feedback mouse wheel and other control wheels
98 6,125,385 Force feedback implementation in web pages
99 6,104,382 Force feedback transmission mechanisms
100 6,104,158 Force feedback system
101 6,101,530 Force feedback provided over a computer network
102 6,100,874 Force feedback mouse interface
103 6,088,019 Low cost force feedback device with actuator for non-primary axis
104 6,078,308 Graphical click surfaces for force feedback applications to provide user selection using cursor interaction with a trigger position within a boundary of a graphical object
105 6,067,077 Position sensing for force feedback devices
106 6,061,004 Providing force feedback using an interface device including an indexing function
107 6,057,828 Method and apparatus for providing force sensations in virtual environments in accordance with host software
108 6,050,718 Method and apparatus for providing high bandwidth force feedback with improved actuator feel
109 6,046,727 Three dimensional position sensing interface with force output
110 6,037,927 Method and apparatus for providing force feedback to the user of an interactive computer simulation
111 6,028,593 Method and apparatus for providing simulated physical interactions within computer generated environments
112 6,024,576 Hemispherical, high bandwidth mechanical interface for computer systems
113 6,020,876 Force feedback interface with selective disturbance filter
114 6,020,875 High fidelity mechanical transmission system and interface device
115 6,015,473 Method for producing a precision 3-D measuring apparatus
116 5,999,168 Haptic accelerator for force feedback computer peripherals
117 RE36,387 Percussion input device for personal computer systems
118 5,959,613 Method and apparatus for shaping force signals for a force feedback device
119 5,956,484 Method and apparatus for providing force feedback over a computer network
120 5,929,846 Force feedback interface device including grounded sensor system
121 5,929,607 Low cost force feedback interface with efficient power sourcing
122 5,907,487 Force feedback device with safety feature
123 5,903,456 Withdrawn
124 5,889,672 Tactiley responsive user interface device and method therefor
125 5,889,670 Method and apparatus for tactilely responsive user interface
126 5,880,714 Three-dimensional cursor control interface with force feedback
127 5,828,197 Mechanical interface having multiple grounded actuators
128 5,825,308 Force feedback interface having isotonic and isometric functionality
129 5,821,920 Control input device for interfacing an elongated flexible object with a computer system
130 5,805,140 High bandwidth force feedback interface using voice coils and flexures
131 5,767,839 Method and apparatus for providing passive force feedback to human-computer interface systems
132 5,739,811 Method and apparatus for controlling human-computer interface systems providing force feedback
133 5,734,373 Method and apparatus for controlling force feedback interface systems utilizing a host computer
134 5,731,804 Method and apparatus for providing high bandwidth, low noise mechanical I/O for computer systems
135 5,724,264 Method and apparatus for tracking the position and orientation of a stylus and for digitizing a 3-D object
136 5,721,566 Method and apparatus for providing damping force feedback
137 5,701,140 Method and apparatus for providing a cursor control interface with force feedback
138 5,691,898 Safe and low cost computer peripherals with force feedback for consumer applications
139 5,623,582 Computer interface or control input device for laparoscopic surgical instrument and other elongated mechanical objects
140 D377,932 Mechanical digitizing arm used to input three dimensional data into a computer
141 5,576,727 Electromechanical human-computer interface with force feedback
142 5,438,529 Percussion input device for personal computer systems